Probe Software Users Forum

Here at the USGS Denver Microbeam Lab we are in the process of having our new JEOL 8530F+ Microprobe installed (YAY!). Everything has been going smoothly up until a couple of days ago when the engineer was checking the performance of the WDS detectors. Without going into details, the GFP counters aren't really working the way they need to be.  Because of the altitude in Denver the atmospheric pressure is significantly different than at sea level and that has a very noticeable affect on X-ray detection using the GFP counters versus the sealed Xenon detectors. It screws with the gain and bias voltages and P/B ratios. Changes in barometric pressure here has a very noticeable effect on the PHAs on our system much more so than I have seen on other instruments at lower altitudes. This is something that we've noticed for years on our old 8900 and we've recognized it and just dealt with it, but with the new probe being installed I wanted to get people's opinions and thoughts on ways to eliminate or minimize the effect of altitude and barometric pressure on the GFP counters.

My questions are: has anyone with a JEOL probe attempted some form of back pressure regulation at the end of the P-10 gas line from the GFP counters? Is this even possible or feasible? Is there some why to safely do this without blowing the detector windows that are under vacuum?

Any input/ideas/help would be greatly appreciated!

Thanks,
Dave

Hi Owen,

Thanks for the reply!

The dibuthyl phthalate in the bubbler is already something that I do on the the old 8900 probe and I also gave some to Ken for the new 8530 probe bubbler. Unfortunately, that does very little to curb the back pressure problems that I experience up here. I also experienced the atmospheric pressure effects when I was running the 8530F in Perth but the effect was less dramatic then what I'm seeing here in Denver.

Thanks again!
Dave

Hi Dave,
In Denver you are at roughly 85% sea level pressure, so I would expect that you can increase the back pressure by 15% and the detector windows should handle it fine.
john

Hi John,

Thanks! That's definitely something I will try when JEOL hands over the 8530 to us. Hopefully that will be a simply easy fix if it works!!

Dave

We got a bubbler from JEOL for our 8530F Plus as well.

I'm wondering why dibutyl phthalate is the fluid of choice (same for the bubblers on our Cameca SX100)? At least in Australia it is a class 9 dangerous substance, and the specified vapour pressure at room temperature is not particularly low either.

Wouldn't it be possible to use something like diffusion pump oil or even rotary pump oil? Many are non-hazardous, much lower vapour pressures. Santovac 5 is terribly expensive of course, but for a single small JEOL bubbler one wouldn't need much.

With the "clean vacuum system" of the newer generation machines, oil-free pumps, on-airlock plasma cleaners, cryo anticontamination etc, what would be the best bubbler fluid? Normally we probably wouldn't expect much back streaming, but if a counter window leaks or breaks...

Cheers,
Karsten

Sorry to hijack, but I've always wondered why the FE instruments come with bubblers and the 8230's don't. ? . I assume there is no technical reason?

D.

Karsten,

This is a good question and I return to my original post. If one put a back pressure regulator at the end of the gas flow chain between the last spectrometer and the bubbler I would guess that that would help solve any atmospheric pressure influences as well as help prevent any back streaming of any fluid (or anything else) in the bubbler in the event of a window failure.

D.

The FE 8530F in Perth, Western Australia didn't come with a bubbler either. I had to scrounge one up. Thankfully there was an old one in a drawer from a previous instrument. I just think JEOL randomly decides whether or not to send it with an instrument.

Cheers,
Dave

Thanks Dave, we probably got the bubbler because we asked for it. The information given to us was that it is optional, so only supplied on request.

Quote from: Karsten Goemann on August 15, 2018, 12:27:39 AM
I'm wondering why dibutyl phthalate is the fluid of choice (same for the bubblers on our Cameca SX100)? At least in Australia it is a class 9 dangerous substance, and the specified vapour pressure at room temperature is not particularly low either.

Wouldn't it be possible to use something like diffusion pump oil or even rotary pump oil? Many are non-hazardous, much lower vapour pressures. Santovac 5 is terribly expensive of course, but for a single small JEOL bubbler one wouldn't need much.

With the "clean vacuum system" of the newer generation machines, oil-free pumps, on-airlock plasma cleaners, cryo anticontamination etc, what would be the best bubbler fluid? Normally we probably wouldn't expect much back streaming, but if a counter window leaks or breaks...

I would think just some cheap silicone based diffusion pump oil would be fine to use as a bubbler fluid, but I have no special knowledge in this area.  Except that at room temperature, silicon oil is not going to be out gassing anything!

Quote from: DavidAdams on August 17, 2018, 05:28:03 AM
This is a good question and I return to my original post. If one put a back pressure regulator at the end of the gas flow chain between the last spectrometer and the bubbler I would guess that that would help solve any atmospheric pressure influences as well as help prevent any back streaming of any fluid (or anything else) in the bubbler in the event of a window failure.

Cameca instruments have a bubbler on the exit of each spectrometer. Do JEOL instruments only have a single bubbler? 

The only advantage I can think of for separate bubblers is that it's easy to see which spectrometer has a broken detector window. Not that it happens very often, especially (never) since we added these "soft start" valves to our roughing pump line:

http://www.vatvalve.com/business/valves/catalog/H/311_1_A

https://smf.probesoftware.com/index.php?topic=120.msg487#msg487

John,

Yes, by default only one bubbler on the JEOL as normally all the P10 channels are in series. I assume one reason for having separate regulators and bubblers on the Cameca would be that they use different pressures ("low" and "high" pressure counters) for different x-ray energy ranges. On the JEOL all P10 counters are at the same pressure as sealed Xe is used for high x-ray energies.

But I've seen at least one JEOL where the P10 line is split upstream from the spectros to have an individual supply for each P10 counter (and I think also a separate bubbler).

I was curious and did some testing on our 8530F+ where the three P10 spectrometers are currently in series. I moved the last spectro in the line on a major element peak, and then did the same for the first and second spectro while monitoring the count rate on the last spectro in the line. There is no noticeable change even at very high count rates on the first two spectrometers. So "recycling" of the gas further down the line does not appear to be affected by what's happening on spectrometers upstream.

I've also heard that one may see differences in count rates when changing the order of the spectrometer in the P10 gas chain on a JEOL instrument, i.e. the spectrometers further downstream can have lower count rates. But I'd assume that may be due to P10 leakage somewhere in the chain, e.g. a leaky detector window, or a tube not attached properly...?


Dave,

I don't have any experience with these back-pressure regulators. I can see how it might help in your case at high altitude, but do you think it would  also make a difference for us, being pretty much at sea level? I.e. in addition to preventing potential backstreaming, could they even out fluctuations in atmospheric pressure? There seem to be a range of designs available. How much of a pressure difference to atmospheric pressure would one have to set for them to operate properly? Obviously too much pressure on the detector windows etc would be a concern.

Cheers,
Karsten

Karsten,

It would be interesting to see if a back-pressure regulator would be useful for JEOL probes at lower altitudes. I think we're going to try one here to see if it will actually smooth out the pressure effects we see. Have you monitored your PHA bias voltages on your P10 counters over time particularly when there is a big change in the atmospheric pressure? In Denver the voltages on our flow counters can often be ≥±10V during large changes in the weather, which, as you can imaging, has a noticeable affect on the analyses being performed. I don't remember what I was seeing when I was in Perth, but I don't remember it being quite so dramatic. The bias voltage on the Xenon counters is almost always the same. The greatest variation on the xenon counters that I've seen here is ±2V and that could be easily attributed to non-pressure related changes. Usually, however, the bias voltage is exactly the same for weeks and months at a time. A back-pressure regulator should, in theory, stop any atmospheric pressure related fluctuations. There are some very low pressure regulator options available (0-10 psi) and from what I understand there doesn't need to be a large pressure differential in those regulators to operate properly. I'm sure that the JEOL engineers will know what the maximum pressure before window failure would be.

Cheers,
Dave

Hi Dave,

In Kingston, at ~100 m AMSL (and no P-10 back-pressure regulator), I see variations in bias voltage required to keep pulse amplitude distributions centered at 4 V using the gas-flow counters (but not with the sealed Xe counters, at least over short periods of time).  These swings can be of similar magnitude to the ones that you report and appear to correlate with variation in atmospheric pressure -- but I need to keep a better record of this in my log file to be absolutely certain.  Even if centering the PHA distribution at 4 V for a given count rate doesn't solve the problem of variation in deadtime with X-ray energy, it sure does provide a useful reference for monitoring fluctuations in the distribution due to various causes.

Brian

For the past ten days I've been collecting data on P-10 gas flow counter anode bias as a function of atmospheric pressure; I've used the pressure recorded hourly at the Kingston airport (93 m AMSL).  I've measured Si Kα on wollastonite while keeping the count rate at 5000 s^-1 and adjusting the bias until I get the PHA distribution centered at 4 V.  I've done this in the PC-EPMA "base level" window using a step of 0.1 V and dwell time of 1 s.

(https://smf.probesoftware.com/gallery/381_31_08_18_7_33_44.png)

Barometric pressure (corrected/adjusted?) averages about 100.5 kPa and usually stays within about 1 kPa of this value.  However, during intense storms in the fall, winter, and spring, it can range as low as ~97.5 kPa.  On the opposite end, after passage of a cold front, the pressure can rise as high as ~103.5 kPa.

I'm going to keep adding data to this plot.  I'm curious to see how much change occurs when barometric pressure is at more extreme values.

Excellent plot Brian, mind if I use it in my WDS lecture?

This is one of the reasons why the SDD-WDS that Ken Moran and Ric Wuhrer have been developing in Australia is a good idea - no pressure sensitivity.

Quote from: Mike Matthews on August 31, 2018, 08:59:24 AM
Excellent plot Brian, mind if I use it in my WDS lecture?

This is one of the reasons why the SDD-WDS that Ken Moran and Ric Wuhrer have been developing in Australia is a good idea - no pressure sensitivity.

Hi Mike,

Feel free to use it as you wish.  It should look much more interesting in a few months.

Brian

Quote from: Mike Matthews on August 31, 2018, 08:59:24 AM
This is one of the reasons why the SDD-WDS that Ken Moran and Ric Wuhrer have been developing in Australia is a good idea - no pressure sensitivity.

And no more lugging around of P-10 gas cylinders!

Thanks, Brian! That's a great plot. I'm going to start doing the same thing on my instruments too. I'll be interesting to compare what you're seeing to what I see. I'm hoping to buy a back-flow regulator too and try it out on one my my instruments to see if that'll have a positive effect.

Dave

I've continued to add data to my plot of GFPC bias versus atmospheric pressure.  Lately we've had some larger oscillations in pressure as is typical of the non-summer months.  I'm curious to know if other JEOL users who have gas flow counters arranged in series see the same pattern that I do:  the spectrometer that serves as the P-10 exhaust 1) requires higher counter anode bias and 2) shows a smaller slope on the plot of bias versus pressure than the one into which the P-10 enters.

(https://smf.probesoftware.com/gallery/381_12_10_18_4_17_37.png)

Hey, it's a 1 million dollar barometer!   ;)

I've been continuing to record GFPC anode bias as a function of atmospheric pressure, and it's becoming apparent that another variable is influencing the bias necessary to keep the PHA distribution centered at 4 V for Si Kα count rate = 5000 s^-1.  During September and early October -- up through October 11th -- the outside temperature oscillated between summer- and fall-like values but was generally above 15˚C and was often above 20˚C.  Since October 12th, though, the temperature has been no higher than 15˚C.  Even though the outdoor relative humidity has been high at certain points since then, dew point temperatures have been much lower than they were before the 12th.  Apparently due to the lower absolute water content of the air, the bias required to keep the distribution as specified above is now noticeably lower for a given value of atmospheric pressure.  In the plot below, I've separated the values I obtained prior to the 12th from those I collected after the 12th.  Note that the effect of atmospheric water is more pronounced for the spectrometer that serves as the P-10 exhaust.  Perhaps some of the scatter in the late summer values is due to variation in dew point temperature, though I haven't checked this.

So the gas-flow counters appear to be both barometers and hygrometers!

(https://smf.probesoftware.com/gallery/381_23_10_18_11_03_05.png)

I can understand the pressure sensitivity, but humidity's a surprise.

If you use tight pha windows they make fantastically sensitive room thermometers too. Four detectors for the price of one :P

I wonder what the mechanism is: water vapour acting as a quench gas, perhaps?

But if the water were behaving as a quench gas, then wouldn't I be getting lower bias values rather than higher ones as air water content increases?  Since H₂O is a strongly polar molecule, maybe it's deflecting the paths of electrons as they approach the anode and is thus reducing the voltage drop at the anode?

To me the variation in counter behavior with room air water content makes sense, as the composition of the counter gas is changing.  Note that channel 1 is more isolated from the atmosphere than channel 4, but both spectrometers are subject to the same variation in room temperature, which does range to a couple °C higher in the summer.

I'm missing something here.

I can see how barometric pressure can affect the detector response simply due to the change in detector gas density, but how can room humidity affect the detector?

I mean the detector gas is coming from the P-10 bottle and constantly flowing so there should be no atmospheric gases getting into the detector.  Right?
john

Maybe I'm wrong, but doesn't the difference in behavior between channels 1 and 4 during both warm and cool weather suggest that atmospheric gases are getting into the counters?  If the effect were due just to increase in counter gas density, wouldn't both spectrometers behave essentially the same?

Awesome stuff. If the humidity in the room is substantial I can see some water vapour diffusing into the detectors against the gas flow, even though it should be constantly purged out again by the P10? But there would be a strong concentration gradient for the water vapour. It might be possible to calculate this from thermodynamics? Water molecules are very effective for charge compensation in variable pressure/environmental SEM. Any water in the detector will probably have some effect.

In any case, probably another reason to put something on the exhaust. I tried filling our bubbler with diffusion pump oil (to avoid the somewhat nasty dibutylphthalate) but it was way too viscous at room T. So now I'm trialling Alcatel 200 rotary pump oil, which seems to have the right sort of viscosity (with bubbler close to half filled 26 nicely shaped bubbles per minute, with P10 pressure regulator set at 16 kPa, flow regulator to around 1.15 ml/minute). From the specs it is hopefully fairly clean and long-term stable ("double distilled hydrocarbon fluid, low backstreaming ... strong oxidation resistance, ... for corrosive applications..."), so I'll see how that goes. It is a double chamber bubbler so even in the case of a detector window failure it shouldn't suck the fluid all the way back into the detectors (in theory, at least...). If anyone has a better idea what to use let me know. I'd still be interested in the back pressure regulator setup even at low altitude such as in our case.

Cheers,
Karsten

Quote from: Karsten Goemann on October 23, 2018, 04:09:13 PM
If the humidity in the room is substantial I can see some water vapour diffusing into the detectors against the gas flow, even though it should be constantly purged out again by the P10?

Hi Karsten,
That is exactly my question.  How could there be air getting in if it's constantly flowing?  Since the gas is flowing, the lines should be very slightly higher than the ambient pressure just due to the resistance to flow by a small diameter long distance line.

Could the room humidity instead be affecting the bias electronics slightly?  Can the bias voltage be monitored?
john

Well the P10 flow is very low (around 1ml/min). One could try using a longer exhaust tube and see if the issue becomes less apparent. But if water vapour can diffuse against the flow due to the concentration gradient the same should be true for air...

I was wondering as well if the humidity could affect the detector electronics. But then the effect should also be visible for the Xe detectors, right?

Cheers,
Karsten

Quote from: Karsten Goemann on October 23, 2018, 05:07:50 PM
One could try using a longer exhaust tube and see if the issue becomes less apparent.

I have ~6.7 m of spare tubing.  I'm going to attach it to the channel 4 P-10 exhaust and resume making measurements.  Currently the length of tubing attached to the exhaust is only 30 or 40 cm (not including the length inside the spectrometer).

Below is a new plot of GFPC bias as a function of atmospheric pressure with ~22 feet of tubing added to the P-10 exhaust.  I've only had a chance to make a handful of measurements in the past few weeks, but it seems clear that the addition of the tubing makes little or no difference.  The cool-weather regression lines do not include the new measurements.

(https://smf.probesoftware.com/gallery/381_23_11_18_5_51_58.png)

EDIT 2018-11-28:  I may have made a conclusion based on too little data.  Measurements that I've made during the past few days suggest that bias actually has shifted to lower values (to get a distribution centered at 4 V at a count rate of 5000 s^-1).  I'll post a new plot at some point during the winter.

Quote from: Brian Joy on October 13, 2018, 01:52:47 PM
I've continued to add data to my plot of GFPC bias versus atmospheric pressure.  Lately we've had some larger oscillations in pressure as is typical of the non-summer months.  I'm curious to know if other JEOL users who have gas flow counters arranged in series see the same pattern that I do:  the spectrometer that serves as the P-10 exhaust 1) requires higher counter anode bias and 2) shows a smaller slope on the plot of bias versus pressure than the one into which the P-10 enters.

(https://smf.probesoftware.com/gallery/381_12_10_18_4_17_37.png)

Hi Brian,

This is really interesting what you've done, I'm hoping to repeat the measurements. I've just taken some measurements today and yes the exhaust spectrometer has a higher voltage. Pressure 997.8 mb, inlet spec 1710, outlet spec 1718

Ben

It's very interesting to see these plots! I'm glad I'm not the only one experiencing this.

What are everyone's P-10 pressures set to? The JEOL engineer here has set our 8530F gas pressure to 0.068 MPa. Does anyone know what the maximum pressure specification for the flow counters is?

Thanks!

Hi,

What type of curve should you fit to a PHA spectra (bias scan) - e.g. Gaussian, etc. So far split pearson 7 seems to work.

Ben

Quote from: Ben Buse on January 10, 2019, 06:39:33 AM
Hi,

What type of curve should you fit to a PHA spectra (bias scan) - e.g. Gaussian, etc. So far split pearson 7 seems to work.

Ben

Hi Ben,

The distribution is usually described as "quasi-Gaussian," with σ < √N, where N is the average number of primary ion pairs produced by an X-ray photon.  Fano (1947, Physical Review 72:26-29) showed that σ = √FN = √FE/ε, where E is the photon energy and ε is the mean ionization energy of the counter gas.  For argon, the "effective" F is usually set at 0.8 and takes into account widening of the distribution due to secondary ionizations produced during avalanching.  See Reed's "Electron Microprobe Analysis," 2nd ed., p. 86-87.

Brian

Here's some initial results

Gas in at Sp3, out at Sp1.

(https://smf.probesoftware.com/gallery/453_22_01_19_8_18_43.png)

Also shown are the maximum height and the FWHM of the bias scan

(https://smf.probesoftware.com/gallery/453_22_01_19_8_22_14.png)

Here's a dumb question:  I know that the JEOL gas flow spectrometers are generally(?) connected in series as Ben mentions above (gas in at Sp3, out at Sp1), but I suspect that the Cameca (gas flow) spectrometers are connected in parallel.

From a recent visit to PNNL, I noticed that their P-10 bottle is tiny and yet they claim it lasts around a year. However on the Cameca there are 5(!) bubblers all running at the same time.  So even though we use a full size cylinder, our P-10 cylinder only lasts about 4 to 6 months.

Does anyone know if the Cameca spectrometers can be connected in series like the JEOL?  Are the any pros vs. cons on this question?
john

Edit by John: Edgar Chavez confirms the Cameca WDS spectrometer P-10 gas flow is in parallel.

Quote from: Probeman on January 22, 2019, 08:48:43 AM
Does anyone know if the Cameca spectrometers can be connected in series like the JEOL?  Are the any pros vs. cons on this question?

I don't think doing in series for Cameca is possible as they run at different pressures ("low" pressure similar to the JEOL P10 channels, and "high" pressure for higher kV where JEOL uses Xe). You would need at least two "chains" one low, one high pressure?

That's probably also the reason that the JEOL P10 bottles last that long? Their overall P10 usage would be equivalent to 1 low pressure spectro on a Cameca?

Cheers, Karsten

Quote from: Karsten Goemann on January 22, 2019, 02:27:02 PM

Quote from: Probeman on January 22, 2019, 08:48:43 AM
Does anyone know if the Cameca spectrometers can be connected in series like the JEOL?  Are the any pros vs. cons on this question?

I don't think doing in series for Cameca is possible as they run at different pressures ("low" pressure similar to the JEOL P10 channels, and "high" pressure for higher kV where JEOL uses Xe). You would need at least two "chains" one low, one high pressure?

That's probably also the reason that the JEOL P10 bottles last that long? Their overall P10 usage would be equivalent to 1 low pressure spectro on a Cameca?

Cheers, Karsten

That's a good point. One would need two systems, one for the 1 atm and one for the 2 atm detectors.  But still one would be using (theoretically) half the gas flow for the two high pressure detectors and 1/3 the gas flown for the others.

Based on the bubble rate I don't think the high pressure detectors flow any more gas than the low pressure detectors.  They're both about one bubble per second.
john

One benefit of the Cameca parallel plumbing is when you've got a leaking counter window it's really easy to see which spectrometer it's on.

Quote from: Mike Matthews on January 23, 2019, 09:58:16 AM
One benefit of the Cameca parallel plumbing is when you've got a leaking counter window it's really easy to see which spectrometer it's on.

That is a very good point.

That said, the 2 atm detector windows very rarely leak as they are 1.5 um(?) Be, and on the three 1 atm flow detectors that our instrument has, one can choose door #1, door #2 or door #3!    ;)

https://en.wikipedia.org/wiki/Monty_Hall_problem

Quote from: Probeman on January 23, 2019, 11:04:28 AM

Quote from: Mike Matthews on January 23, 2019, 09:58:16 AM
One benefit of the Cameca parallel plumbing is when you've got a leaking counter window it's really easy to see which spectrometer it's on.

on the three 1 atm flow detectors that our instrument has, one can choose door #1, door #2 or door #3!    ;)

https://en.wikipedia.org/wiki/Monty_Hall_problem

Hmm, 3 doors and only one is leaking. All you need is three trolls that you're only allowed to ask one question of and you've got a proper riddle.

Quote from: Mike Matthews on January 24, 2019, 10:24:05 AM

Quote from: Probeman on January 23, 2019, 11:04:28 AM

Quote from: Mike Matthews on January 23, 2019, 09:58:16 AM
One benefit of the Cameca parallel plumbing is when you've got a leaking counter window it's really easy to see which spectrometer it's on.

on the three 1 atm flow detectors that our instrument has, one can choose door #1, door #2 or door #3!    ;)

https://en.wikipedia.org/wiki/Monty_Hall_problem

Hmm, 3 doors and only one is leaking. All you need is three trolls that you're only allowed to ask one question of and you've got a proper riddle.

Hi Mike,
Well seriously, it is an interesting dilemma because it would be nice to see which spectrometer has a leaky detector window.  That said, we haven't had a bad detector window since we added these "soft start" values to our roughing pumps about 5 years ago:

https://smf.probesoftware.com/index.php?topic=120.msg487#msg487

And I sure wouldn't mind if our P-10 gas lasted several times longer!

I'll run it by our instrument engineer and see what he thinks...

I've continued to add to my plot of GFPC anode bias versus atmospheric pressure over the past few months.  It appears that the addition of 22 feet of tubing to the channel 4 exhaust had little or no effect, and this is a little puzzling.  I expected the added tubing to at least reduce the amount of scatter present in the measurements on channel 4, but the magnitude of the scatter appears unchanged.

(https://smf.probesoftware.com/gallery/381_01_02_19_8_45_22.png)

Clearly at least one other independent variable (in addition to atmospheric pressure) is important in order to account for scatter in the plot.  In the following plots, I've contoured indoor dew point temperature versus atmospheric pressure for anode bias in 4 V increments.  Although the plots would benefit from some more measurements, it seems clear that water content of the atmosphere affects the anode bias required to keep the distribution centered at 4 V (while maintaining count rate at 5000 s^-1), even with the added tubing.  So I'm sticking to my claim that air is actually mixing with P-10 in the gas-flow counters.  On the plot above, as dew point decreases (to as low as ~-5°C in the past month) the anode bias for given atmospheric pressure also decreases.  (In the summer, dew point temperature ranges as high as ~+15°C.)

(https://smf.probesoftware.com/gallery/381_01_02_19_8_34_38.png)

(https://smf.probesoftware.com/gallery/381_01_02_19_8_36_34.png)

I'll keep adding to these plots at least through next summer to see if my results from late last summer are reproducible.  By the way, I'm keeping track of dew point with the Lascar EL-USB-RT thermometer/hygrometer, which displays temperature and dew point in real time and also periodically dumps data to a file.  It can be gotten at Amazon for about $60 U.S.

Hey Karsten,
In October 2018 you said:

Quote from: Karsten Goemann on October 23, 2018, 04:09:13 PM

In any case, probably another reason to put something on the exhaust. I tried filling our bubbler with diffusion pump oil (to avoid the somewhat nasty dibutylphthalate) but it was way too viscous at room T. So now I'm trialling Alcatel 200 rotary pump oil, which seems to have the right sort of viscosity (with bubbler close to half filled 26 nicely shaped bubbles per minute, with P10 pressure regulator set at 16 kPa, flow regulator to around 1.15 ml/minute). From the specs it is hopefully fairly clean and long-term stable ("double distilled hydrocarbon fluid, low backstreaming ... strong oxidation resistance, ... for corrosive applications..."), so I'll see how that goes. It is a double chamber bubbler so even in the case of a detector window failure it shouldn't suck the fluid all the way back into the detectors (in theory, at least...). If anyone has a better idea what to use let me know. I'd still be interested in the back pressure regulator setup even at low altitude such as in our case.

Cheers,
Karsten

What was the outcome of your experiment? I'm going through the same process.
Dawn

Hi Dawn,

I still have the Alcatel oil in the bubbler and it seems very stable (no discolouring, no change in the level, constant bubble rates...). I don't have a dataset similar to what Brian has done to be able to verify if and how much it reduces drift in the bias settings. I'm hoping it does not only prevent air (with changing humidity) backstreaming into the detectors but also to have at least some backpressure regulating effect.

Cheers,
Karsten

Below is a more or less final version of my plot of GFPC anode bias versus atmospheric pressure:

(https://smf.probesoftware.com/gallery/381_15_10_19_8_51_22.png)

In contrast to previous versions of the plot, I've now contoured it (by hand/eye) for dew point temperature, and I've also color-coded the data.  The curves that I've drawn on the plot are given by the following equations, which work well for interpolation:

Channel 1:  bias [V] = 7 V/kPa * P_atm [kPa] + 0.52 V/°C * T_dew [°C] + 909.4 V
Channel 4:  bias [V] = 7 V/kPa * P_atm [kPa] + 0.76 V/°C * T_dew [°C] + 929.7 V

Some unexplained scatter is still present on the plot, and so additional variables are likely significant in addition to atmospheric pressure and dew point temperature.  For instance, I don't really have a good handle on time required for equilibration, which obviously would be particularly important when atmospheric conditions are changing rapidly.

When determining the appropriate anode bias, I should note that I used the JEOL "base level" scan rather than the "high voltage" scan and then adjusted the bias in 2 V increments until I got a distribution centered at/near 4 V.  I made the final scan using a step of 0.1 V and dwell time of 1 s; generally I repeated the slow scan at least once in order to assure reproducibility.  This is a tedious process, but it produces better results than the "high voltage" scan, which tends to have a broad, gently sloping "peak."

(https://smf.probesoftware.com/gallery/381_15_10_19_8_49_48.png)

So I guess now I need to do something about this problem.  I'm reluctant to add liquid to the bubbler at the exhaust, as I worry about backstreaming in the event of counter window failure.

Wow, Brian!! This is a fantastic data set! I'm really happy that you took the time to do such intensive testing and compile all this. This definitely shows VERY similar behaviour to what I have observed for a lot of years. As to a fix, I'm still scratching my head on that myself.

I don't think you should be too concerned about backstreaming. I've had fluid in all of my instruments and have also had window failures. I've never had any fluid pulled back into the system. The key seems to be to only fill the bubbler to just where the bubbles start and no more.

-dave

I've attached a copy of the measurements in an Excel file in case anyone wants to examine them more carefully and/or plot them differently.

I have no experience or knowledge with Jeol probe construction, but I am very familiar with Cameca probes. I want to point to some very important physical behaviors/issues which can influence the observed optimal bias drift and is more plausible to proposed water diffusion against gas flow.

At first, It is not enough to be sure that your room temperature is rock stable. Can gas bottle be heated by floor or wall? (Or more precisely how different room air temperature gets in contrast to wall and floor temperatures (in day cycles, in seasonal cycles)? Hopefully the bottle is not outside of lab - that would be the fatal flaw). Air humidity is very important in air <-> object temperature exchange rate. The higher humidity - the faster object's temperature equalizes to the temperature of the air. Temperature of the bottle influences the temperature of P10, and so that influences the density of the gas in the proportional counter which will shift optimal bias value. Same counts for the probe, just differently to static bottle, probe has lots of heat sources and many passive and active cooling solutions. So even if Air temperature in the room is kept extremely stable, the humidity variations will change the temperature of the objects. BTW, pressure also affects the cooling rates.

I want also to point out that between setting bias value (or scanning bias values with digital interface that is Your computer and software, or values which You are displayed on the screen) there is the complicated electronic system which in different parts is actively and passively cooled. So again, any change in humidity will swing lazily/carelessly designed analog signals and that will result in observable PHA shifts and optimal bias shifts. On some instruments there are such design atrocities as analog signal squeezed-down (down-voltaged) with primitive voltage divider (pair of resistors) which will toss the PHA left and right depending from humidity... And changing proportional counters with SDD's wont change a lot. The EDS systems (where electronics part has much better engineering) has exactly same issues (spectrum shift after humidity change), at least I am aware of these in our labs.

Perhaps you could present some actual data to support your argument??

Quote from: sem-geologist on September 10, 2020, 03:56:49 AM
I have no experience or knowledge with Jeol probe construction, but I am very familiar with Cameca probes. I want to point to some very important physical behaviors/issues which can influence the observed optimal bias drift and is more plausible to proposed water diffusion against gas flow.

At first, It is not enough to be sure that your room temperature is rock stable. Can gas bottle be heated by floor or wall? (Or more precisely how different room air temperature gets in contrast to wall and floor temperatures (in day cycles, in seasonal cycles)? Hopefully the bottle is not outside of lab - that would be the fatal flaw). Air humidity is very important in air <-> object temperature exchange rate. The higher humidity - the faster object's temperature equalizes to the temperature of the air. Temperature of the bottle influences the temperature of P10, and so that influences the density of the gas in the proportional counter which will shift optimal bias value. Same counts for the probe, just differently to static bottle, probe has lots of heat sources and many passive and active cooling solutions. So even if Air temperature in the room is kept extremely stable, the humidity variations will change the temperature of the objects. BTW, pressure also affects the cooling rates.

I want also to point out that between setting bias value (or scanning bias values with digital interface that is Your computer and software, or values which You are displayed on the screen) there is the complicated electronic system which in different parts is actively and passively cooled. So again, any change in humidity will swing lazily/carelessly designed analog signals and that will result in observable PHA shifts and optimal bias shifts. On some instruments there are such design atrocities as analog signal squeezed-down (down-voltaged) with primitive voltage divider (pair of resistors) which will toss the PHA left and right depending from humidity... And changing proportional counters with SDD's wont change a lot. The EDS systems (where electronics part has much better engineering) has exactly same issues (spectrum shift after humidity change), at least I am aware of these in our labs.

Quote from: Brian Joy on September 10, 2020, 06:12:29 PM
Perhaps you could present some actual data to support your argument??

I should apologize at first. I forgot to say thank You a lot for this extensive excellent measurements and data. I wish I could had this at hand 6 years ago and could show that under nose of our management, so they would not cheapskate on air conditioning (AC) system in our lab.

I am not questioning credibility of data, I am questioning only the proposed mechanism for observed bias drifts.
So lets look to my claims step by step.

I have no humidity logs in our lab, albeit there is plan for those. The hardware is sitting and waiting for configuration, but I had no time to configure it. I have at the moment only extensive temperature data (logged every 1 minute for a bit more than a year with some brakes) from different places such as outside wall near window (old site for AC control panel (and internal thermometer used for T control), inner build wall where P10 gas bottle is presently placed by (also a new site for AC control panel), P-10 bottle metal case, backside of EPMA (air at 20 cm from floor, 10 cm from microprobe), microprobe chasis at two points (column isolation valve screw (EP6), junction of second ion pump and column).

(https://drive.google.com/uc?export=view&id=1etm1jGzHkHfzg1yME7cNQEgonjlvmXkb)

Initial idea for thermometer network came from some weird behavior of one of spectrometers, so I wanted to see if air streams from AC are not effecting more one of the spectrometers (the one with weird behavior) and so wanted to measure separate temperatures for every spectrometer (using DS18B20, digital 1-wire thermometers connected in network). Before I started long term logging I had re-modified the network to troubleshoot vacuum leak problems (I was suspecting either metal gasket of that valve or metal gasket of second ion pump, thus the weird positions given below). Also I had expanded that network with other points in lab to prove that AC control panel was initially badly placed, and P10 Gas bottle had to be moved from external wall to internal wall (I was getting critique from management for moving stuff, and needed hard proof). After P10 gas movement we saw a lot of improvement in calibration stability, but that was not enough. Unfortunately I started logging temperatures with that network only after AC and P10 Gas placement modifications, so I can't compare directly with old setup. You can see in above picture that at winter the temperature of outer wall gets much cooler, and gas bottle (when it was standing by outer wall) was also surely affected. Also AC logic within c/p in old place was often getting very biased temperature readings. I.e. in cold winters we were getting very warm room (i.e. when -20 C outside), while I have no data record from those times, it was very obvious for human senses.

I should mention that our AC panel is set to keep in between 23 (start cooling if above) and 22 (heat up if below) degrees, and integrated thermometer reading on AC c/p is showing 22 or 23 whole year. I also should mention that previously we had in room installed some USB temperature humidity logger which was also showing very stable temperatures (Multimetrix DL 53), basically lulling us into believing that there is no issues. That useless piece of USB logger was installed by Cameca with our new probe. The "PRO" thermometers/loggers have one significant drawback - they are encased in plastic packaging and measure highly averaged temperature - they measure something from alternative reality - or like going to listen for opera but putting the bucket on the head. That is why I made network of thermometer chips (DS18B20) which are bare-exposed to the stuff which it is supposed to measure (i.e. direct contact to gas bottle with thermal paste in between chip and bottle, but well isolated from direct air blow; or other example - directly exposed/hanged in the air for air temperature measurement - so that room humidity and air streams would affect the thermometer in exactly same manner as the machine). Before assembling the network of thermometers I had tested them all by simultaneously measuring temperatures while keeping them immersed in same liquid container to see that they get exactly same (+/- 0.0625 C) temperatures in range of 30-15 degrees. So the temperature differences showed in charts are not artificial but real. DS18B20 is able to differentiate temperatures with 0.0625 C steps, which is pretty good and it is able to capture not only daily and seasonal temperature fluctuations but also individual AC cooling/heating cycles. (In the end this precision helped me to locate and fix vacuum leak).

The temperatures are pretty stable during autumn, winter and spring. As an example 4 days during stable period:
(https://drive.google.com/uc?export=view&id=1Y6bt0JoCJNPmRE9UXC6Zjb62KA1xOCnq)

However it is pretty terrible during hot summer days:
(https://drive.google.com/uc?export=view&id=1x61WSucsS49LwlBYYfJH-IjtwBnk3SSk)

Here comes so waited autumn, which begins the stable cycle again (the figure below depicts logged temperatures with transition from hot summer weather changed with atmospheric front going through location and lowering outside temperatures):
(https://drive.google.com/uc?export=view&id=1FI-lQ94NjQMGX91Rz4GBChNtlu6e5ZOc)

This I think summarizes currently gathered all temperature measurements:
(https://drive.google.com/uc?export=view&id=1IRQW6YL3S11SUA7PlS8Iu8hlJOjiN41l)

So why during summer our lab gets so bad variations? I think (I still need to install humidity measurements hardware to be 100% sure) that it is so at summer as lab is coolest place compared to the surrounding rooms and halls in the building and gathers/traps humidity, that is outside from lab (inside building) and outside of building temperatures gets significantly higher during hot day than inside the lab. The increased humidity significantly increases the rate of feedback between air conditioning injected cold air streams and AC c/p (where we can see very steep negative peaks recorded on all temperature readings). As control panel logic recognizes that AC is over-cooling it switches off AC very rapidly and waits for threshold to be crossed again. Thus there is much larger cycles than during stable period, where AC works in PID mode (like i.e. water chiller; it is integrating temperature measurement and controlling AC air stream strength and temperature not so violently - thus on chart we see smaller cycles which switches much more often). And so these are the data which I base my question about if being sure that room temperature is rock stable, and being sure about all heat fluxes.

Talking about P10 gas temperature and its influence to counting, I have rather "anecdotal" experience without real measurements (sorry, no data). When we change P10 gas, old calibrations gets instantly outdated; But then after some time the newly made calibrations gets outdated, and old calibrations gets again to be good. The effect is clearly correlative with temperature differences between lab room, that is: if weather is mild (spring or autumn) and temperature of transported bottle is similar to our lab, then there is no or very week calibration misalignment observed. But if gas bottle is transported and changed at cold winter or hot summer, we get 1-2 weeks of constantly out-dating calibrations until gas temperature stabilizes with room temperature. Then we can use again old calibrations. I know that gas bottles are stored in some not-heated or cooled shed by gas producer, and so its temperature equilibrates with environment/weather before being transported to our lab.

Now talking about electronics, most of datasheets of electronic components present in one or other form how the values of described component react to temperature changes and (optionally) humidity. Resistors are particularly sensitive to temperature and so rating can change (and so voltage values, i.e. which are fed into ADC, or other way around - the digital values which are converted from digital to analog and amplified (there are always some resistors in control loops of OPAMPs in most cases)). I don't think I can give any data for that.

JEOL uses metal film resistors where necessary; these typically have tempco = 50 ppm/°C and also low voltage coefficient.  As far as op amps, even the humble 741 is specified by TI to have an average input offset voltage drift of 15 µV/°C; for variation of a few degrees C, this drift is at least an order of magnitude lower than the input offset voltage specified at 25°C (typical maximum = 1 mV, 5 mV guaranteed [for +/-15 V supplies]).  For a precision op amp, the corresponding values are at least an order of magnitude lower.

Can you present data to show that the centroid of the pulse amplitude distribution shifts position significantly (perhaps a few hundred millivolts) as a function of temperature (in any part of the lab or instrument)?  Of course, as you pointed out, the water content of the air will tend to rise as temperature of the air rises, and so the issue becomes more complicated.

I'm not trying to say that I have all the answers, but I can show conclusively that the PHA centroid varies systematically with variation in dew point temperature as well as atmospheric pressure.  Though I presented a suggestion to explain the effect, I can't prove a cause-and-effect relationship -- only a correlation.  I collected data over a period of more than a year and found the results to be largely reproducible, even when comparing data from different seasons.  Of course it's difficult to compare values from summer and winter here, as the winter dew point T in the lab rarely exceeds 5°C, and summer values typically fall between 10 and 15°C.  I never write in terms of relative humidity since a given value only applies at a specified temperature.

I also obsess over temperature in the lab (though maybe not quite as much as you), and I also have to deal with people who think that temperature variation is of no consequence.  I see effects on peak positions (for all diffracting crystals, not just PET) and count rates (including sealed Xe counters), and I attribute this to expansion and contraction of metal parts as temperature varies.  Obviously this will change the geometric relationship between sample surface, diffracting crystal, and counter window.  JEOL spectrometers are constructed almost entirely of brass, which has a relatively large coefficient of thermal expansion. 

Quote from: sem-geologist on September 11, 2020, 07:38:50 AM
Now talking about electronics, most of datasheets of electronic components present in one or other form how the values of described component react to temperature changes and (optionally) humidity. Resistors are particularly sensitive to temperature and so rating can change (and so voltage values, i.e. which are fed into ADC, or other way around - the digital values which are converted from digital to analog and amplified (there are always some resistors in control loops of OPAMPs in most cases)). I don't think I can give any data for that.

Quote from: Brian Joy on September 11, 2020, 02:30:20 PM
I also obsess over temperature in the lab (though maybe not quite as much as you), and I also have to deal with people who think that temperature variation is of no consequence.  I see effects on peak positions (for all diffracting crystals, not just PET) and count rates (including sealed Xe counters), and I attribute this to expansion and contraction of metal parts as temperature varies.  Obviously this will change the geometric relationship between sample surface, diffracting crystal, and counter window.  JEOL spectrometers are constructed almost entirely of brass, which has a relatively large coefficient of thermal expansion. 

I also have obsessed about temperature stability in the lab, though now that we have that under control in our new facility it never enters my mind any longer.

I agree with Brian that PET crystals show the largest changes in intensity with respect to temperature, but I note this previous post from him on this question:

https://smf.probesoftware.com/index.php?topic=854.msg5422#msg5422

Brian: how much of the intensity change on PET crystals do you now think is due to temperature changes, and how much to exposure to the beam (electron trap issues)?  On Cameca instruments we don't need (or have) electron traps because all our crystals are behind "column separation" windows.  But I still saw significant intensity changes, especially on my PET crystals, correlated with temperature though I can't place my hands on the data at the moment.

Quote from: Probeman on September 13, 2020, 09:59:54 AM
Brian: how much of the intensity change on PET crystals do you now think is due to temperature changes, and how much to exposure to the beam (electron trap issues)?  On Cameca instruments we don't need (or have) electron traps because all our crystals are behind "column separation" windows.  But I still saw significant intensity changes, especially on my PET crystals, correlated with temperature though I can't place my hands on the data at the moment.

Ah yes, fond memories...

The effects of failure of the static filter depended on Bragg angle.  I routinely monitor Ca Ka count rate, and, at this peak position, the decrease in count rate due to failure of the static filter was small (2 or 3 per-cent).  Although it pains me to do this, below I've presented a plot of Si Ka count rate on PETL at a point in time before failure of the filter and also after; both scans were collected under identical conditions.  The variation in count rate that I attribute to variation in lab temperature is in the range of 1%.  I haven't investigated the effect systematically because I'm not willing to subject the lab to abnormal temperature variation intentionally.  The changes in peak position with varying temperature are obvious, especially on PET.  At any rate, I think the plot below will answer your question.  By the way, I now monitor Si Ka count rates on the PET crystals, and I also check the static filter periodically with an electron mirror.

(https://smf.probesoftware.com/gallery/381_13_09_20_12_38_38.png)

Just looking back through this as I'm once again having fun with fluctuating standards as weather fronts come through. We dropped about 20 mbars in 24 hours whilst I was doing low overvoltage for major elements and light elements and started seeing ever-worse totals! I think I must be running the standards more than the unknowns at this point.

The plots of barometric pressure vs detector bias chime well with what I see on both our EPMAs (SX100 and 8530F, in very different buildings). I've plotted up temperature (as measured in lab and external) vs raw count rate for our standards as part of longer runs (same beam conditions etc) and see little correlation, but a strong correlation with ambient pressure – and obviously much worse for our P10 than Xe counters (although still visible on those).


Looking at these plots:

Quote from: sem-geologist on September 11, 2020, 07:38:50 AM
The temperatures are pretty stable during autumn, winter and spring. As an example 4 days during stable period:
(https://drive.google.com/uc?export=view&id=1Y6bt0JoCJNPmRE9UXC6Zjb62KA1xOCnq)

However it is pretty terrible during hot summer days:
(https://drive.google.com/uc?export=view&id=1x61WSucsS49LwlBYYfJH-IjtwBnk3SSk)

I'd say you've got an air con unit set at 22C with a +/-1C accuracy. Of all the coloured lines, only the dark green one really tells you what is going on. 

In winter, its gently warming the room to within minimum temperature (21C), which takes very little effort and results in the stable temperature profile you're seeing.

In summer, the air con only seems to be active during daytime hours, when there is a much greater rate of temperature rise (probably the Sun!). The temperature in your lab shoots up quickly above 23C, the air con switches the compressor on and blasts cold air into the lab, resulting in the rapid cooling of the air temperature. This is repeated during the day. What's interesting in this case is that overnight, your air con doesn't come on at all (or if it does, in a very low power mode), and what is probably the drop in ambient temperature brings the lab temperature back down. It seems to switch on about 7am and off again at maybe 6 or 7pm?

Jon, thanks for comment,

There are few problems causing this kind of fluctuations at summer.
(1) our external units of split AC are situated on the sunny roof top. Roof is tar type (black). We had once AC outer unit failure when outside was 35 C (in the shadow, no wind, quite high humidity), now try to imagine what a hellish conditions would be there on the roof (I guess surface temperature easily up to 60 C if not more at normal sunny day). It is badly planned, such stuff happens then institutions buy instruments and place it in some "free" space completely not designed bottom-up for that specific function.
(2) our lab is at second floor, fortunately at least from all-day-shadow side. However room has windows! and there is some reflected light (and heat) from other building. But most important thing is that the room is 3D island of cool 😎 from all sides and from bottom and up. That makes it perfect humidity sink as outside is hot, and corridor and rooms at sides and bottom and top are very warm. Humidity can raise up during day up to 70 %. The higher humidity - the worse AC can cope with keeping the set temperature.

This summer was better, as I found usage case for our second AC. Due to previous AC failure we had installed side-wall simple cheap AC as emergency AC. We normally had not run it, as pretty soon after installation I found out that its maximally-cooled wind-blow would make metal gaskets of our SXFiveFE leak. However, this summer I found out that it can work as dehumidifier and keep the humidity in check (< 60 %), which makes our main AC work more stable. In Dehumidifying mode it does not blow air, thus it does not influence our SXFiveFE directly.

Quote from: sem-geologist on October 01, 2021, 02:42:29 AM
...such stuff happens then institutions buy instruments and place it in some "free" space completely not designed bottom-up for that specific function.

I was saying something similar to a colleague of mine earlier today. Perhaps we should all start looking at running microprobes in pressure controlled fridges!
Your air con seems to be doing a decent job of cooling the lab though, it just does it all at once and then nothing. It must be like being sat in an arctic gale when it activates! 

Quote from: sem-geologist on October 01, 2021, 02:42:29 AM
I found out that it can work as dehumidifier and keep the humidity in check (< 60 %), which makes our main AC work more stable. In Dehumidifying mode it does not blow air, thus it does not influence our SXFiveFE directly.

Where we are in the UK, I don't think there's a dehumidifier in existence that could get our humidity below 60%.

Quote from: JonF on October 01, 2021, 07:53:15 AM
I was saying something similar to a colleague of mine earlier today. Perhaps we should all start looking at running microprobes in pressure controlled fridges!

Here is a nice schematic of "gauge" vs. "absolute" pressure:

(https://smf.probesoftware.com/gallery/395_01_10_21_12_15_46.png)

Here's an example that goes to 30 psi, so maybe would take care of our barometric pressure induced P-10 changes from weather fronts:

https://store.mathesongas.com/3396-single-stage-high-purity-absolute-pressure-regulator-brass/

Has any tried using one of these so called "sub atmospheric" (absolute pressure) gas regulators for their P-10 flow?

The problem is that with sub-atmospheric pressure You will have no flow, as gas from lower pressure wont move to higher, but contrary. The only way for this to work would be to release sub-atmospheric pressure P10 into lower pressure (i.e. vacuum buffer). Of course we don't want to release it into current vacuum system (even primary) as that could contaminate vac system; however I think using a small low power pump (most important something not loud, as labs are already buzzing annoyingly) for such buffer for releasing gas from low-pressure counters could be very financially feasible and quite simple to achieve. This is really interesting concept, it could at last put some end to endless redoing of standard measurements forced by weather change... unless gas is not the only weakness (but probably it is as we see no such fluctuations on high-pressure spectrometers despite weather changes).

Yes, exactly.  All these regulators (if you read the company details) are vacuum pump backed for positive flow.

I had a similar (homemade) differentially pumped detector flow system at UC Berkeley in the 1990's based on Henke's design from LBL. It ran pure propane gas at sub-atmospheric pressures for better detection of nitrogen. Obviously the (separate) vacuum mechanical pump was vented to a fume hood!  30" of vacuum is all one needs for such a system.

But I am hoping that these regulators will run at 15 or 30 psi (absolute) and as you say, because they are referenced to vacuum, might provide more pressure stability.

Of course what we really need are solid state detectors for our WDS spectrometers!

QuoteOf course what we really need are solid state detectors for our WDS spectrometers!

I am completely not sure about that. Why? (1) it probably could be ok replacement for low pressure counters; However providing very stable cooling of such detector is very challenging. We probably could use cooled nitrogen and same capillary to transport heat from the SDD. To cool SDD means there should be enough pressure of nitrogen, or lower pressure nitrogen but cooled to some low temperatures (then lots of liquid nitrogen is required). SDD and its counting electronics drift depends from temperature and humidity (We need to calibrate EDS SDD on SEM much more often than on EPMA, as the air conditioning is less sophisticated there, and SEM experiences more temperature swings (the SDD itself is cooled at stable set temperature, the decalibration is clearly a response to temperature and humidity variations by pulse counter unit (EDS SDD electronics))). This is why I am also not 100% sure that PHA drifts are directly produced alone only due to atmospheric changes, and rather suspect that electronics react to atmospheric changes too, in particularly that EPMA shaping and counting electronics is much less sophisticated from EDS pulse processing units, and low pressure counters most often works at lower BIAS and much higher GAIN (which means that gain-OPAMPs can swing the signal much more, than on high-pressure low gain spectrometers).

Partly problem with low pressure counters are the PHA drift. But if You use integral mode, there is no problem, as You still are counting same amount of counts (the counter bias can be set higher or lower in some margins which does influence pulse height, but not so pulse density).

SDD can look as that nice stuff, but there are many artefacts which would influence measurement linearity in particularly at low energies and is very hard to resolve:
incomplete-charge - no such thing on proportional counter
Si esc peaks - on proportional counter we have Ar esc, but for low energies it is not applicable.

Generally new design of proportional counter electronics could solve most of proportional counter problems (PHA resolution, pile-ups, increase linear throughput, intelligent bias offset depending from room temperature), while there would be no need to hardware changes inside spectrometer.

Actually there is no obstacle to use the last one NOW. Stick some digital thermobarometer (hygrometer) in the room. Log the values, apply some low-pass filter. Make correlation curves between bias and environment. Add some code to PfS to adjust bias depending from room environment -> profit.
   

Below is a final update on my plot of the effects of variation in barometric pressure and atmospheric water content on Si Kα pulse amplitude distribution using JEOL P-10 gas-flow counters.  Previous plots weren't contoured quite correctly because I'd made the approximation that the anode bias required to keep the distribution centered at 4 V varies linearly with respect to dew point temperature.  In truth it varies linearly with H₂O partial pressure, and the plot now reflects this.

As before, I've contoured the plot by eye, with contours represented by the following linear equations:

Channel 1:  bias [V] = 7 V/kPa * P_atm [kPa] + 7.5 V/kPa * P_H2O [kPa] + 905 V
Channel 4:  bias [V] = 7 V/kPa * P_atm [kPa] + 11.8 V/kPa * P_H2O [kPa] + 922.5 V

Over the relevant range of temperatures, P_H2O is given well enough by the following relation:

P_H2O [kPa] = 0.611 kPa * 10^((7.5 * T_dew [°C]) / (237.3°C + T_dew [°C]))

Based on scatter in the plot, it's obvious that other variables have important effects on the pulse amplitude distribution at given count rate, but I don't necessarily know what they are.  Time is undoubtedly one of those variables, as equilibration certainly doesn't occur instantaneously.

(https://smf.probesoftware.com/gallery/381_22_05_22_6_35_40.png)

(https://smf.probesoftware.com/gallery/381_24_05_22_3_56_31.png)

Brian,
That is really nice work! Do I understand clear - T in a room was all the time stable and changing humidity and atmosphere pressure were moving this dew point (so severely)?

Quote from: sem-geologist on May 28, 2022, 08:07:05 AM
Brian,
That is really nice work! Do I understand clear - T in a room was all the time stable and changing humidity and atmosphere pressure were moving this dew point (so severely)?

No, temperature in the lab is not necessarily stable.  I have no choice but to work with the data I'm able to collect while I work to minimize temperature fluctuations.

Temperature is taken into account in the plot in the sense that, as temperature rises, the maximum dew point temperature also rises.  For instance, the points that plot as open circles were collected during the past two summers during periods when the air conditioning was overloaded.  Since the temperature in the lab was anomalously high (up to ~24°C), this allowed the dew point temperature to reach ~17°C (65% relative humidity at 24°C) on a few occasions.  Typically, with lab temperature at ~21°C, I wouldn't expect to see values in excess of 15°C (69% RH), which is already way too high for a variety of reasons.  At any rate, most data on the plot were collected when lab temperature was in the range 20.5°C +/- 1°C.

For each X-ray counter, warm, humid summer days plot in the upper middle (black dots), while cool, stormy days plot to the lower left, and cold, dry winter days plot on the far lower right (blue dots).

Quote from: Brian Joy on May 29, 2022, 12:18:23 AM

Quote from: sem-geologist on May 28, 2022, 08:07:05 AM
Brian,
That is really nice work! Do I understand clear - T in a room was all the time stable and changing humidity and atmosphere pressure were moving this dew point (so severely)?

No, temperature in the lab is not necessarily stable.  I have no choice but to work with the data I'm able to collect while I work to minimize temperature fluctuations.

Temperature is taken into account in the plot in the sense that, as temperature rises, the maximum dew point temperature also rises.  For instance, the points that plot as open circles were collected during the past two summers during periods when the air conditioning was overloaded.  Since the temperature in the lab was anomalously high (up to ~24°C), this allowed the dew point temperature to reach ~17°C (65% relative humidity at 24°C) on a few occasions.  Typically, with lab temperature at ~21°C, I wouldn't expect to see values in excess of 15°C (69% RH), which is already way too high for a variety of reasons.  At any rate, most data on the plot were collected when lab temperature was in the range 20.5°C +/- 1°C.

For each X-ray counter, warm, humid summer days plot in the upper middle (black dots), while cool, stormy days plot to the lower left, and cold, dry winter days plot on the far lower right (blue dots).

Quote from: JonF on October 01, 2021, 07:53:15 AM
Where we are in the UK, I don't think there's a dehumidifier in existence that could get our humidity below 60%.

I see improvement at summer with second (cheap) Air conditioning working as dehumidifier. It keeps RH below 60%. Well, We are in the middle of Europe, maybe that does not compare at all to wet climate. Also rooms for our probes are pretty small, it is enough just for 2 probes. I saw some pictures of other labs, and those looks spacious - it would not make me surprised that simple dehumidifier would not work. Maybe solution (financially possible) would be to put the probe together with AC and 2nd AC as dehumidifier in small space, leaving control PC and control panel outside (Something like plexiglass separation of the room).

Quote from: sem-geologist on May 30, 2022, 12:39:32 AM
I see improvement at summer with second (cheap) Air conditioning working as dehumidifier. It keeps RH below 60%. Well, We are in the middle of Europe, maybe that does not compare at all to wet climate. Also rooms for our probes are pretty small, it is enough just for 2 probes. I saw some pictures of other labs, and those looks spacious - it would not make me surprised that simple dehumidifier would not work. Maybe solution (financially possible) would be to put the probe together with AC and 2nd AC as dehumidifier in small space, leaving control PC and control panel outside (Something like plexiglass separation of the room).

That's a good idea, and it's something that I discussed last summer with the department manager.  The lab is in the basement and is partially underground, but it has windows, and so a window unit could be a possibility.  Also, last summer it came to light that physical plant services had been adding the wrong refrigerant to all the AC units in the building; the resulting refrigerant mixture was highly ineffective.  If lab temperature and humidity are still difficult to control this summer, then I'll probably push for a window unit.  Unfortunately, nothing is cheap at Queen's -- we're forced to work with contractors chosen by the university, and then the university marks up the price by something close to a factor of ten (no joke).

Other improvements (like venting heat from the building properly and pre-drying air) would help but are prohibitively expensive.  It seems a little silly to me to have to worry so much about heat and humidity in a place where a 30-degree summer day is considered a "scorcher."