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Old 17th Sep 2021, 7:51 pm   #1
space_charged
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Default Edwards pirani 501 gauge and head

I've acquired an Edwards 501 gauge controller and I'm after some information about the
connections to the gauge head. Either the circuit diagram for the 501 gauge controller or the head which is an Edwards PRE10K would be of help.

The head connects to the controller via 7 pin DIN socket. Any information as to what each pin connects to would be of help.

A bit about this type of gauge:
These gauges were used on such things as vacuum furnaces and read from atmospheric pressure down to about 1*10E-3 torr. They are 'medium vacuum' gauges and not particularly accurate. They need to be calibrated at atmospheric pressure and at at (or beyond) their lowest pressure.
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Old 18th Sep 2021, 5:19 pm   #2
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Default Re: Edwards pirani 501 gauge and head

I have opened the gauge controller and been looking at the PCB, in particular the connections to the DIN socket. This shows that only THREE pins are connected to the circuit.
That simplifies the problem considerably. Two of the pins must be connected to the bridge in the gauge head itself. The third must be the 'sense' connection. The circuit has only one IC and that is a quad OP amp. Only one of the OP amps is actually used so the circuit is really simple.
I have a spare Edwards pirani gauge head (PRCT-10K) and I'm going to try to connect it. The gauge head needs to have 'set atmosphere' and 'set vacuum' pressure calibration pots. From circuits I have from other Edwards gauge heads, I can see were to put these and I have approximate starting values for calibration.
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Old 18th Sep 2021, 9:41 pm   #3
Bazz4CQJ
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Default Re: Edwards pirani 501 gauge and head

Pirani gauges were part of my working life in a chem lab back in the 70's. We had a two-stage system, the first stage using a rotary oil pump that pulled down to about 10-3 torr on a good day and then a second stage with a diffusion pump which would go down to about 10-6. We didn't use them to measure or set a specific vacuum, but they told you a lot about how the system was running; a significant leak would mean you could not reach the normal levels, and tiny leaks meant you could get there, but more slowly than normal.

Don't think that ours used DIN plugs. Sorry I have no tech info. Somewhere in the garage I have a box of Pirani bits and a few Penning bits which I think were good to lower levels than the Pirani. I don't think I've ever found out what sort of vacuum was pulled inside valve envelopes before they sealed them.

I have a vacuum oven, but my needs are such that it uses only a mechanical gauge.

B
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Old 19th Sep 2021, 4:39 am   #4
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Default Re: Edwards pirani 501 gauge and head

Thanks for your reply Bazz4CQJ on my Edwards 501 pirani gauge controller.

As I type this (yes I know its 4 in the morning) I'm doing a calibration run on the 501 gauge. As I said earlier I've fitted an Edwards PRCT10K to the controller along with two pots for calibrating it at atmosphere and at the lowest pressure a pirani can read.

I did most of the preliminary calibration just using the backing pump but that can't 'bottom out' the pirani. Once I'd got it roughly right I started the run I'm in the middle of now. The diff is running and the pressure in the bell jar is now way below what a pirani can read so gives me the zero point.

My system is equipped with an Edwards 1005 which has two pirani heads and a penning CR25 (cold cathode magnetron gauge). That has just passed 9*10E-5 torr.

Pirani gauges can read down to about 1*10E-3 torr. Some get a bit lower than that. Penning gauges go MUCH lower, down to 1*10E-11 torr or lower. A penning gauge was taken on an Apollo mission to the moon to measure the pressure at its surface. (Yes there is a slight atmosphere on the moon). The only problem with penning gauges is that it can be difficult to get them to 'strike' at very low pressures. Some use radioactive sources inside them to help with that. If you have any old penning gauge heads that is something to watch out for. At the sort of pressures I deal with striking the pening isn't a problem and in any case I switch the penning on at 1*10E-4 torr, where it strikes easily.

I've made some simple electron guns and also my own fluorescent screens so I can see the beam. Also made a very simple triode once that even drove s speaker vis a valve output transformer.

As to the vacuum in valves, well in fact the high vacuum was 'pulled' by the getter being fired. The valves would be pumped first of course but once the getter fired the resulting vacuum would have been of the order of 1*10E-7 torr.

Residual gas in the valve would degrade the cathode by poisoning it so they tried to get the vacuum as good as possible to extend life.

Thanks for your interest in my little problem.
Charles
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Old 19th Sep 2021, 12:08 pm   #5
DMcMahon
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Default Re: Edwards pirani 501 gauge and head

When I worked on Ion Implantors some of the systems used Edwards Pirani and Penning gauges, older systems using non Active gauges and later systems using the Active gauges. Much older systems used Ion gauges and Thermistor (T/C) gauges (non Edwards)

As already stated the Pirani is used for rough vacuum usually pumped by a wet or dry rotary pump and the Penning used for when the system goes into hi-vacuum, then being pumped by either Cryo (cryogenic) pumps or Turbo (turbo molecular) pumps (older systems using Diffusion pump for one vacuum chamber).

Somewhere I should have various of the Edwards manuals as soft copy on CD but trying to find them will be very difficult, will look though.

David

Last edited by Cobaltblue; 19th Sep 2021 at 1:59 pm. Reason: Thermistor instead of Thermocouple as corrected by OP
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Old 19th Sep 2021, 2:34 pm   #6
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Default Re: Edwards pirani 501 gauge and head

Quote:
Originally Posted by space_charged View Post
As to the vacuum in valves, well in fact the high vacuum was 'pulled' by the getter being fired. The valves would be pumped first of course but once the getter fired the resulting vacuum would have been of the order of 1*10E-7 torr.
That's interesting. Assuming that the envelope was originally filled with air, it sounds as though the getter was sufficiently reactive to react with both the oxygen and the nitrogen present?

The system which worked with was used to transferring small quantities of hydrogen fluoride in to other chemical mixtures; essentially a condensation process. Needless to say, we had some fairly elaborate means of trapping out any residual HF before it got to the pumps... and hence in to the outside world!
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Old 20th Sep 2021, 9:52 am   #7
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Default Re: Edwards pirani 501 gauge and head

Interesting about the HF.

For some semiconductor implants Boron Trifluoride (BF3) was used as a source gas when implant species such as Boron, BF2 and Fluorine were required, an unwanted by product of this potentially was Hydrofluoric acid, the nasty liquid form of HF in water. Hydrofluoric acid is also used in the Semiconductor industry, one main use is for etching (cleaning) Silicon wafers.

David
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Old 20th Sep 2021, 11:04 am   #8
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Default Re: Edwards pirani 501 gauge and head

Quote:
Originally Posted by DMcMahon View Post
When I worked on Ion Implantors some of the systems used Edwards Pirani and Penning gauges, older systems using non Active gauges and later systems using the Active gauges. Much older systems used Ion gauges and Thermistor (T/C) gauges (non Edwards)

As already stated the Pirani is used for rough vacuum usually pumped by a wet or dry rotary pump and the Penning used for when the system goes into hi-vacuum, then being pumped by either Cryo (cryogenic) pumps or Turbo (turbo molecular) pumps (older systems using Diffusion pump for one vacuum chamber).

Somewhere I should have various of the Edwards manuals as soft copy on CD but trying to find them will be very difficult, will look though.

David
David

Did you work at Applied Materials in Horsham? The vacuum systems you describe sound exactly like what I worked on there for a while.

John
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Old 20th Sep 2021, 12:40 pm   #9
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Default Re: Edwards pirani 501 gauge and head

Yes John I worked there for more than 30 years, I left (made redundant) in early 2007 shortly before the whole factory was closed down.

David
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Old 20th Sep 2021, 6:34 pm   #10
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Default Re: Edwards pirani 501 gauge and head

David

You have a PM.

John
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Old 28th Sep 2021, 2:06 am   #11
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Default Re: Edwards pirani 501 gauge and head

I've now got the 501 gauge controller working with the modified PRCT-10-K pirani gauge head. I have had to re-calibrate the controller so it reads correctly. For that I used the original scale as the basis and drew a new one using a drawing package. I calibrated it against my existing Edwards 1005 pirani/penning controller then printed the new scale. The scale is held in place by the transparent cover for the meter and the original scale is underneath, should I ever come across the correct gauge head.

The two photos attached show the head connected to my small HV system and the display as it now is.

The system shown is my small air cooled HV system which uses an Edwards E05 air cooled diff pump which I run on DC704 (diff oil). It gets the system down to 3*10E-05 torr in about an hour when I'm using my largest bell jar.

I have a larger HV bell jar and am about to fit a turbomolecular pump to that (Leybold TW70H).
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Old 28th Sep 2021, 3:36 am   #12
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Default Re: Edwards pirani 501 gauge and head

Interesting! That kit is much more recent than I recall using. Last time I did any serious vacuum work was ~2006, but I still have an old rotary pump and a small oven.

B
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