Adding a New Meter to TC Gauge Controlelr

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Robert Dwyer
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Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

So, a while back I purchased a surplus CVC GTC-365 controller for cheap that was compatible with the GTC-036 tube that came with the pneumatic valve I had bought back in July. This controller is powered by a 1.5V "D" battery put into the back of the unit, and can also work with the GTC-004 tube if needed (which I do have new).

Now, after pumping down my test vacuum system (simply the flange with the gauge, the vacuum connection, and the valve), for about 30 minutes and seeing no movement on the gauge, I new that the controller may be a bust. I tested it with GTC-004 also, and there was still no movement. However, with a few quick tests with a multimeter, I found that the current the controller was outputting was to the exact specifications in the manual, and that the "current adjust" knobs for calibration was changing the current.

After finding that the controller is doing what it is supposed to with regards to outputting the current needed, I turned my attention to the actual meter on the unit itself. With a few closer looks I found that the meter's needle and casing looked a bit busted up. I took out the meter, looked inside, and found that it indeed has been subjected to some very rough treatment and broke as a result. I tried to fiddle around with fixing it a bit, but things eventually got to a level above my level of experience.

Since the controller itself is working as it is supposed to, but just the meter is a problem, would it be possible to just connect a new voltmeter to the controller and calibrate it so the voltage read is equal to a specific pressure in microns? Or is it just better to get a different controller?
John Futter
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Re: Adding a New Meter to TC Gauge Controlelr

Post by John Futter »

Robert
has the meter got a label that gives its resistance and something like "FSD = 100uA"
What we need to know is the meter sensitivity in the case just above this would be 100 microamps for full scale.
If you can find this on the meter somewhere then all you need is a meter that is the same Full scale deflection (FSD)

look carefully and let us know whet you find
Robert Dwyer
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

Just looked on the meter, and in the bottom right hand corner it says "FS 200 UADC"

So a meter with this same specification would work then?
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Re: Adding a New Meter to TC Gauge Controlelr

Post by John Futter »

Robert
Yes but 200uA is not as common as 100uA which would work fine with an added parallel resistor equal to the resistance of the 100uA meter across the meter terminals.
Robert Dwyer
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

Ok, thank you John,

just to clarify though, I can try to get a 200uA meter (which is rarer), or a 100uA meter with a resistor added to its terminals in parallel (with the resistors value being that of the resistance of the 200uA meter)?
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Re: Adding a New Meter to TC Gauge Controlelr

Post by John Futter »

Robert
no the resistor to be the same as the 100uA meter
We do this so 100uA goes through the resistor and 100uA goes through the meter making 200uA in total

all good
Last edited by John Futter on Tue Jan 17, 2017 1:03 am, edited 1 time in total.
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Richard Hull
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Richard Hull »

It is to be remembered that a new meter must replecate the grossly non-linear micron scale markings as well. An adroit hand could effectively create and paste a new scale on the new meter which will certainly be linearly marked to 200ma. It may be difficult to find a same size replacement in this day and age. I own this same great little gauge controller and it is now my number one tester of off-line roughing pumps at the head. Cute, slick and convenient.

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
Robert Dwyer
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

Hello,
I understand this is an old thread, but just to add an update, I did get a new meter, and it does seem to work. When I turn the calibration nob the needle responds. It also does sense a vacuum and reads down to about 4000 microns (not impressive, but the pump does have problems needing to be resolved), but it is probably grossly un-calibrated. I'll probably get a digital gauge to try and calibrate it with.
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Richard Hull
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Richard Hull »

4000 microns!!!!!! 4 torr?? This is just wrong.............. Totally whacked out.

The TC tubes that you claim you have will not even indicate that high a pressure! Explain.

What about a photo of your meter face indication under vacuum. I assume you created a new scale for the new meter??

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
Robert Dwyer
Posts: 89
Joined: Sun Sep 04, 2016 5:34 pm
Real name: Robert Dwyer

Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

I agree, either something is wrong with the gauge/tube or the pump I was using. I tested it recently on an old 5CFM two-stage Chinese refrigeration pump that was new, but after 30 minutes I got no indication of a vacuum. I ended up taking apart the pump and found what seemed like rust having built up on the pump stages, and a chip out of one of the pieces of metal on the first stage. This of course prompted me to ask for a refund on that pump . I did make a new scale and I attached it to the meter. I have run the tube under a different pump also about 2 weeks ago, (a fisher scientific Maxima C Plus), and got a slight movement (to the 5000 not 4000 micron range after a 2 hour pump time and no further movement), but I cannot try and test it again on that pump, because the seal between the chamber that holds the oil and the rest of the pump crumbled to pieces after trying to take the pump apart to clean it, so now the pump will not even hold oil! I must say, bad luck with pumps! The Fisher Scientific pump was sold as used but in working condition so I am in the process of debating whether to try and fix the pump/seal or just try to get a refund on it. With these discoveries I realized the readings are probably due to the fact that I had bad pumps. According the GTC-365 manual the GTC-035 tube has a range of 5000-0 microns, but the fact that the needle only moved to the 5000 micron reading after 2 hours is very pathetic. Sadly without knowing I have a good pump, I cannot have a clear way to test exactly what is going on. Still, the guage needle does move and respond when calibrating , so I have hopes that the gauge is working well (will be getting a digital gauge for comparisons though). Here are the pictures of the setup I was using, though I believe the problem now lies with the pumps:

20170219_102800.jpg
Every attachment in the setup was sealed with Dow Corning vacuum grease.
20170219_102809.jpg
The meter is connected via two copper wires attached to the bolts due to the fact that the meter was a bit too small to fit snugly into the old meter's socket.
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Richard Hull
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Richard Hull »

This is exactly the scale that is on my meter. You seem to have done such a fine job on testing everything there is in the box previously, so I have little doubt an issue exists there.

The new meter has a polarity just like the old one. Are you sure you got it right? Try swapping the leads. Battery in to proper polarity? Can you adjust the TC tube current at all and see meter deflection. What resistance do you have in parallel.... if this is a 100ua meter? Does your replacement meter really read 100ua or 100ma? It must read 100ua or 200ua if you got an exact replacement.

Was there a resistor in series or parallel with the with the original defective meter?

You really need to check all this out and report fully. I bet the fix is simple either throught error or mis-connection. This controller is abysmally simple.

Richard
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
Robert Dwyer
Posts: 89
Joined: Sun Sep 04, 2016 5:34 pm
Real name: Robert Dwyer

Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

The new meter is a 200ua meter. The battery is in the proper position. There is meter deflection when I adjust the current. Looking back at the old meter I did however find, a small resistor attached in series within the meter. Perhaps I should take the resistor and place it within the new one?
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Richard Hull
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Richard Hull »

You say there was a resistor within the old meter? Was it across the terminals or in series to one of them. Real important.

The classic metering required for all TC gauges was an odd ball 9mv (millivolt meter)!!! The manufacturer of the guage may have had the 200ua meter in the original factor altered to be a 9mv meter of the proper resistance.

Te beat goes on.

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
Robert Dwyer
Posts: 89
Joined: Sun Sep 04, 2016 5:34 pm
Real name: Robert Dwyer

Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

The resistor was in series with on the black wire leading from the terminal to the glavanometer.
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Richard Hull
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Re: Adding a New Meter to TC Gauge Controlelr

Post by Richard Hull »

The correct meter for use with a T/C gauge is a 10 or 14 millivolts meter with a 55 ohm impedance. If you don't have this, in the end, you will not have a proper reading. Much of this is covered in the FAQ found in this forum FAQs

viewtopic.php?f=25&t=10098

The Bell Jar article can't be beat for a full explanation to the tubes and metering and how to roll your own T/C gauge for just the price of the tube and a few common electronics junk bin parts. Read it.

It sounds like you need to make that 200ua meter into the above reading meter Without the device and your old and new meters in hand, I can't help you beyond that.

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
Robert Dwyer
Posts: 89
Joined: Sun Sep 04, 2016 5:34 pm
Real name: Robert Dwyer

Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer »

Alrighty, thank you very much. I shall set off to do this and give an update on the progress.
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