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Edwards Pirani Gauge/Display Troubles

Posted: Sun Dec 11, 2016 12:18 pm
by Tom McCarthy
Hooked up my Edwards RV3 to the chamber last night, along with Pirani sensor and display to see how it performed.

Quickly ran into trouble with my setup though, as the display didn't show any change in pressure, it just sat around its normal atmosphere point. If I gave the display box a firm (light) whack, the needle would swing down from atmosphere to somewhere in the 100 micron range, but would return straight to atm. If I whack the display box with the sensor at atmosphere, there is no swinging of the needle. If I blow into the sensor in open air, the display registers some increase in pressure, swinging beyond the atm mark. The orange light on the display (see picture) flickers a little bit when the sensor is under vacuum, no flickering when the sensor is at atmosphere - I don't know if that 's relevant.

I know there's some level of vacuum being produced by the pump - When I open the KF flanges, there's quite a bit of sucking and whooshing as the chamber comes back up to atmospheric pressure - the problem isn't the pump.

So, the problem seems to be that the readout isn't properly showing what the sensor measures. The reason I don't suspect the sensor as much is that there is some response on the readout to changes in pressure (ie swinging from atm to 10 - 100 micron and back with a tap), so the sensor seems like it's sending back a signal, just the display isn't showing it properly.

I guess my next step would be to confirm the sensor is working. From reading old posts, Chris Bradley described these as 'glorified voltmeters' and advised a voltage across the two appropriate pins on the lead and read the voltage signal output, seeing how it changes with pressure and checking against the calibration curve. http://fusor.net/board/viewtopic.php?f= ... ani#p26491 The connector on the sensor is a weird one - have attached a picture, anybody able to identify it?

Is this the right way to proceed? Would anybody have any goto suggestions for what could be going wrong and how to fix it?

Thanks,
Tom
pr10-k gauge vacuum.jpg
Display looks exactly like this when connected to vacuum.
Display looks exactly like this when connected to vacuum.
Connector on the end of the Pirani's lead
Connector on the end of the Pirani's lead

Re: Edwards Pirani Gauge/Display Troubles

Posted: Sun Dec 11, 2016 3:50 pm
by Jerry Biehler
It's a cinch jones connector. Still available but not used much anymore. I would be pretty surprised if it is not a bad pirani tube, they are the most delicate part of the unit.

Re: Edwards Pirani Gauge/Display Troubles

Posted: Sun Dec 11, 2016 4:44 pm
by Richard Hull
Maybe a bad solder joint in the box electronics or internal plug to circuit board. Just a thought since whacking the box made a difference.

Richard Hull

Re: Edwards Pirani Gauge/Display Troubles

Posted: Mon Dec 12, 2016 10:47 am
by fizz
Hi Tom

Try putting the Head directly on the pump inlet then watch the needle go across the meter, so long as you pump is ok !

Robin

Re: Edwards Pirani Gauge/Display Troubles

Posted: Tue Dec 13, 2016 5:00 pm
by Tom McCarthy
Thanks Jerry, you might be right. I'm unsure though, will see how things go with help here!

I thought the same Richard, have taken a quick look at the innards, doesn't seem like any glaring issues at present (although I'm no expert).

Robin - I was about to email you before I saw your post, speak of the Devil!

I deadheaded the gauge and the needle did go across meter, but went straight from atm to 10^-3 torr and even further past that, the needle did slow down as it approached the end of the meter. When the pump is switched off, the needle immediately heads back towards atmosphere. When the gauge is returned to atmosphere pressure, the needle does a little jump back to about 6 torr before returning to sit at atm. Does that point to anything glaring?

The pump is an Edwards RV3, rated for 1.5 microns, so going past 1 micron seems unlikely.

Tom

Re: Edwards Pirani Gauge/Display Troubles

Posted: Tue Dec 13, 2016 11:31 pm
by Jerry Biehler
There is a slight possibility it just needs to be calibrated. But to do this you need to have it attached to a system that will go down to at least the -4 range.

Re: Edwards Pirani Gauge/Display Troubles

Posted: Wed Dec 14, 2016 9:01 am
by fizz
Thanks for thinking of me Tom !

What you have described is normal except for the head reading off scale @ 10-3, your pump is rated @ 3.7m3h-1 so its pumping a tiny
Pirani tube with a volume of 8 cm3 its just like one big gulp of gas to get to 10-2 then quickly gets to the pumps ultimate of around 5x 10-3 mbar, if you are useing Ultragrade 19 Oil, I would reset the Pirani heads Vac pot to read just short of the 10-3 reading.
I hope that helps you.

Robin

Re: Edwards Pirani Gauge/Display Troubles

Posted: Wed Dec 14, 2016 4:48 pm
by Tom McCarthy
No problem - Thanks for the help!

Is it normal that the needle heads back to atm when the pump stops running? There's still vacuum in the deadheaded volume when the pump is turned off, so that seems strange - Unless I have an abominable leak, but this seems unlikely as if I leave the pump off for a while and then open up the KF flange, there's a noticeable resistance to opening up the flange, and I can hear the air whooshing in.

So to reset - Just turn the potentiometer on the head when pump's running until it reads at about 10-3? Found a document here for Pr-10 gauges: http://mfc.engr.arizona.edu/documents/E ... 157880.pdf

section 4.1.1 outlines the reset procedure. As Jerry mentioned, if I can get someone who has a confirmed sub 10-4 system, they could reset it accurately for me. I'm not sure my pump is actually doing the 1.5x10^-3 torr it's rated for, so I'm not sure how accurate resetting it myself would be.

I am using Ultragrade 19.

Jerry, thanks too for your help.

Tom
Edwards Pirani Datasheet D021-57-880
Edwards Pirani Datasheet D021-57-880

Re: Edwards Pirani Gauge/Display Troubles

Posted: Wed Dec 14, 2016 5:32 pm
by Jerry Biehler
No, most pumps should hold a significant portion of their ultimate vacuum when shut off. There is a anti-suckback valve that closes when the pump stops. If it did not close you would have a sensor full of oil.

Re: Edwards Pirani Gauge/Display Troubles

Posted: Thu Dec 15, 2016 1:35 pm
by fizz
Hi Tom

Have you used the Gas ballast on the RV3 ? If not and the oil is still a clear through the sight glass open the GB switch on ll (full ) for a couple of hours , just in case there are contaminants there ,do this with the pump inlet sealed off, once the pump has done its time close the GB switch and allow to cool half hour should be OK.

You have never said that the pump has been tested for its ultimate pressure anywhere I can see,
but the Pirani head showed <10-3, if you adjusted the Vac pot like I said to just above the 10-3 line.

Once the pump has cleaned itself and cooled, put the head back on and see what you can obtain again, it should be the same reading or may be a little better, if it again shows 10-3 adjust the pot to appx 2 x 10-3 this lies at half a millivolt on the bottom scale on the meter, with that done you should be very close to true, always remembering that Edwards quote an accuracy of +- 30% of reading when new! Anyway why do you need to know to the nearest mbar as these instruments are normally just for indication between 1 mbar & 10-2 to run a diffusion pump.

The RV3,5,8 pumps all have a quoted total pressure measurement of 2 x 10-3 Mbar when new.

Regarding the pressure rise it could be a leak but I doubt it, but just vapour, I always advise people to have there gauge heads adapted to an isolation valve like an Edwards SV10 so that you can protect the filament from an inrush when dismounting the head.

Robin

Re: Edwards Pirani Gauge/Display Troubles

Posted: Thu Dec 15, 2016 2:56 pm
by Tom McCarthy
I haven't used the gas ballast yet - have been operating cold with high vacuum mode and gas ballast closed. The oil is a little cloudy, so I'm going to have a go at decontaminating it and if that doesn't work I'll change it. I'll run the pump with GB II as you've advised for a couple hours tomorrow evening.

The gauge is behaving itself quite well now, just need to set the vacuum pot after running the pump.

You're right, I don't really need the gauge to be all that accurate. I'm using it with a Turbovac 151 too, so fore-vacuum only needs to be about 1mbar anyways.

I'm not quite happy with the pressure rise. The RV manual says it's probably something up with the inlet valve (not the gas ballast as I've had it closed), should I open it up and see if I can spot anything?

Thanks again for all the help.

Tom

Re: Edwards Pirani Gauge/Display Troubles

Posted: Thu Dec 15, 2016 5:09 pm
by John Futter
Cloudy oil
rise in pressure after switch off = water vapour

You need to run the pump for an hour dead headed ie blanked off with the gas ballast wide open

No longer than this otherwise it will throw out all its oil

The gas ballast introduces a bit of air to help shift the water from the pump to outside the pump.
Never run the pump with the inlet open you will quickly fill the pump oil with water out of the atmosphere

Re: Edwards Pirani Gauge/Display Troubles

Posted: Fri Dec 16, 2016 11:39 am
by fizz
I have said SV10, but it should be SP10 give me a call.

Re: Edwards Pirani Gauge/Display Troubles

Posted: Sat Dec 17, 2016 11:02 am
by fizz
Hi Tom

I have said the model # of the valve is SV10 this is incorrect and should be SP10 , Email me about this item.

Robin

Re: Edwards Pirani Gauge/Display Troubles

Posted: Sat Dec 17, 2016 12:23 pm
by Tom McCarthy
Ran the pump with Gas Ballast open for an hour yesterday evening - that helped a little bit. Followed it up with 2 3 hour long runs. Oil is now 100% clear and as long as Gas ballast is closed when pump turned off, it holds the vacuum. Opening the gas ballast introduces a little leak, but I think this is to be expected.

Looks like it's all good then, will try a couple more runs to confirm it's ok.

Thanks for all the help.

Tom

Re: Edwards Pirani Gauge/Display Troubles

Posted: Sun Dec 18, 2016 5:39 pm
by Tom McCarthy
Have continued playing with the pump and gauge.

The pumping is perfect now, goes straight down to 10ish microns with gas ballast closed, oil is clear. However, turn the pump off and we're in quite a gradual return to atmosphere. Actually, sometimes it goes to about 500 microns and other times the whole system levels at about 200 microns. I'm suspecting a leak rather than pump issues now - I make sure to keep the inlet closed off as best I can so as not to get any more water vapour in it and oil is totally clear. (One thing that's odd is when the gas ballast is open and pump is running, the oil stays clear, but fills with little bubbles moving through it). Unless there's still some dodgy vapours or leftovers hanging around in the pump, I think the pump is running fine. Leak is on the order of 3-5 microns a second, or thereabouts.

The system is just pump inlet <> KF attach to a Lesker valve <> KF25 - KF15 Adapter <> KF10 o-ring to gauge. From reading past posts, there's been mention that valves are 'notorious' for leaks, outgassing is the other suspect. Looks like it's time to
a) get out the industrial cleaning wipes and wipe down insides of connections
b) get my hands on some cans of Dust-Off for checking leaks

If this isn't the way to go, please let me know! Or, if there's any quick fixes for checking out what's up, do let me know. I'm a bit suspicious that the setup is leaking as it seems so minimal. Vacuum is hard though - http://fusor.net/board/viewtopic.php?f= ... eck#p68662

Tom
Current setup
Current setup