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 » Tue Jan 17, 2017 12:49 am

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?
If we throw more money at it, it will have to work... right?

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Re: Adding a New Meter to TC Gauge Controlelr

Post by John Futter » Tue Jan 17, 2017 12:57 am

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 » Tue Jan 17, 2017 1:18 am

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?
If we throw more money at it, it will have to work... right?

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Re: Adding a New Meter to TC Gauge Controlelr

Post by John Futter » Tue Jan 17, 2017 2:28 am

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 » Tue Jan 17, 2017 2:43 am

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)?
If we throw more money at it, it will have to work... right?

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Re: Adding a New Meter to TC Gauge Controlelr

Post by John Futter » Tue Jan 17, 2017 5:34 am

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 6:03 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 » Tue Jan 17, 2017 6:00 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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

Post by Robert Dwyer » Sun Feb 19, 2017 12:59 am

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.
If we throw more money at it, it will have to work... right?

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Re: Adding a New Meter to TC Gauge Controlelr

Post by Richard Hull » Sun Feb 19, 2017 2:21 am

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Robert Dwyer
Posts: 80
Joined: Sun Sep 04, 2016 9:34 pm
Real name: Robert Dwyer
Location: New Mexico

Re: Adding a New Meter to TC Gauge Controlelr

Post by Robert Dwyer » Sun Feb 19, 2017 6:15 pm

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.
If we throw more money at it, it will have to work... right?

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