TC gauge reading problem

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Alexander Ziemecki
Posts: 74
Joined: Mon Aug 21, 2023 6:25 pm
Real name: Alexander Ziemecki

TC gauge reading problem

Post by Alexander Ziemecki »

Hey everyone, I've got a fil-tech TC004-KF16 thermocouple gauge tube ( ... 16-flange/) . I'm having some trouble getting a reading off it. I don't know if it's broken or just a PEBCAC.
The website claims it is a drop-in replacement for the hastings DV6 tube. However, I am starting to doubt that claim.

I'm putting 17 mA over the heater pins, and reading nothing off the TC pins. The output should be between 0-9.5 mV, according to the attached graph.
tcguage p v graph dv6.png
The graph uses an amplifier to shift 10 mV into 1 V, but the shape should be the same. I should be getting SOME non-zero reading at ATM, and i'm not. Additionally, I know that my vacuum chamber produces SOME kind of vacuum, because I can feel it and hear it when i turn the pump off. Following Richard's advice, the tube is attached as directly to the roughing pump as possible, and you can audibly hear when the pump is done pushing out atmosphere and switches to ironing out the dregs of low pressure. But still, I get no reading at all off the TC pins.
Screenshot 2024-04-16 163133.png
I've tried checking if the manual is simply wrong about which pins are which, and putting power over those instead. I'm pretty sure this busted my first TC tube. I got a new one, but sawed the first one open just to see what was in it, and this is what I saw.
That gauge was from Ebay, and so I wouldn't be surprised if maybe it was broken when I got it (although I did read a resistance off each pin, before I think I blew it). Also, I definitely cut into the filaments when I opened it with the saw, so that damage is inconclusive. However, this current gauge, the same model, I ordered directly from the manufacturer, and so it should work.

My multimeter has enough sensitivity to read into the 1 mV range, before it gets lost to noise around 0.3 mV. Why am I not getting anything off the meter?

Is it a scam tube? The website says it's a drop-in for a dv6, but the dv6 gets its readings of pins 1,3,7, and 8, not 1,3, 5, and 8 like this one does. What's going on with this tube?

Attached to this post is all the documentation that the manufacturer had for the part when I reached out. I've also been trying to study the dv6 documentation, which is leaving me confused by the differences. Axcellis, the other tube manufacturer this tube is said to be a drop-in for, seemed bewildered when I called and asked them for documentation on their tc gauges, and I couldn't find anything online. So I don't know what's going on.

Any assistance would be appreciated. Thanks.
TC004 (1).pdf
(1.7 MiB) Downloaded 20 times
TC004 Operating Characteristics.pdf
(734.59 KiB) Downloaded 22 times
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Dennis P Brown
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Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

Re: TC gauge reading problem

Post by Dennis P Brown »

The issue I found with those types of TC gauge sensors is that few (any?) are interchangeable. I've tested over a dozen different models (different numbers/letters) and none work with my reader except the exact model originally designed/sold with the reader. I would not trust any TC gauge except the exact model designed for the read out unit no matter what the vendor claims. As for working accurately up/towards atmosphere, I've never had one (even very high end units) that didn't consider a few torr as atmospheric pressure.
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Richard Hull
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Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: TC gauge reading problem

Post by Richard Hull »

Common TC gauges never start reading until about 1 torr =1mm=1000 microns pressure. There are specialty TC gauges with special meters demanded for reading that can work in the low torr ranges.

My favorite and best gauge tube is the 1518 tube as it tends to read and have some tiny bit of useful range well below 20 microns. This is provided you do a lot of fancy calibrating with special electronics and interpolation tables. The DVM-6 tube is more or less the industry standard based on Hastings long and storied history with TC gauges. In general, the use of the 1518 and the TC004 can serve well running off one 1.5 volt D-cell, one pot, one milliammeter to read the heater current and a special millivolt meter rated and scaled for their use. See diagram above.

There is a great article in the Bell Jar that tells how to make your own TC gauge using a number of the more popular tubes.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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