What's so special about controller cables?

[Chris Roberts]

Hello,

I just found a hot cathode ionization controller from my university's surplus for $10. It is missing its cable, so I was looking around for replacements and noticed that they are running about $100. Not wanting to spend 10 times as much on the cable than the controller itself, is there anything stopping me from making improvised connections with regular wires? Thanks for your help.

-Chris

[DaveC]

Chris -

There's nothing really special about the cables... other than the plug for the collector pin on the top of the ion gage. Use a piece of coax.. with an insulating push-on plug... but anything will work. The other plug is the 4 inline pin plug for the filament and grid connections on the ion tube. Some amp push-on female sockets will work well there, too. The cable should be about 16 gage minimum for the filament current.

Each cable should have a shield.. since the ion gage currents can get pretty small... roughly proportional to the pressure...and noise will give you false high readings.

Depending, on your display unit, the plug there could octal, or rectangular ... and collector pin cable usually goes directly to a separate BNC.

Dave Cooper

[John Futter]

Chris

this is how the OEMs get a bit more dosh$$ special connectors and cables.
Varian, Vacuum Generators and Leybold are spectacular in special cables /connectors /pricing

see Daves comments
do not use PTFE coax if you are going for extremely low vacuums it is piezo electric and any vibration will give a false reading use a good PE or PE air dielectric cable for the collector electrode.

Turbos also have the same problem with connectors and cabling

I can help if anyone is wanting to make a Leybold tmp50 ,150,360, 361 type cable up

[Doug Coulter]

I'd second the above remarks, and add that *any* piece of coax is also a microphone if there's DC on it, usually the ion collector voltage, due to the capacity changing a little with flexing -- what you "ground" the shield to matters here. You can always stuff your wire into a conduit to reduce this a lot, if there's not much vibration from other things like a mech vac pump.

I've had one vacuum system manuf admit to me they do this pricey cable thing on purpose. Makes sense with a low sales volume. Sometimes it's hard to escape as the oddball connectors they use are expensive themselves due to low volume at distributers of such things. The oddball ones Pfeiffer uses for their gages cost $12 ea at DigiKey for example.

To get really low readings the ion currents are VERY low, on the order of e-12 and (well) below. Cleanliness of all insulators really counts here -- and this is even the reason the ion collector comes out of a different part of the tube than the other wires -- the glass itself is too conductive, and they use one of the better insulating glasses.

The filament and grid connections aren't critical at all by comparison. This is based on ion gages I've made from scratch. That ion collector is really the hard part, and even tempts me to try to find a low enough power electrometer amp that I could put it right into the tank itself (heat is hard to get rid of there, and most COTS stuff will just fail due to melting itself even at milliwatt levels unless you have a good conduction path to the outside).

[Larry Upjohn]

Wow;
You got a much better deal than I did at $60.00USD. I discovered the same problem with missing cables. I was able to get a partial manual in PDF format but it is missing the pages with schematics and pinouts for the TC and ION gauge detectors. I have been able to trace out the ION guage pinout just from the circuit funtional description but the description for the TC gauge is much more vague. Steve Hansen's description of my TC Gauge (DV6M) gives the detector specs and pinouts but I haven't gotten around to making cables yet. Was able to measure up the connectors on the back of the controller and figure out the AMP socket/Plug combination and the associated parts were less that $5.00 new from Mouser(No connection financially). 8 Pin Octal relay sockets will work for the TC gauge and Duniway stocks a plug kit for the Hot Cathode ION gauge for $30.00 apiece. I have one question for the group though. If you use coax to the Collector wire what do you do with the coax shield. It would seem that if left unconnected it would be a lot of capacitative load on the Electrometer amplifier input and therefore subject to High frequency noise as well as microphonics from simply motion of the cable.

P.S. The controller I have is the Varian 880 version with 2 TC gauges as well as the ION guauge. If anyone has a clue about the pinouts of the two connectors I would be most grateful. More later, Larry Upjohn.

[Chris Roberts]

Thank you all for your advice. One final question, how would I figure out which of the four gauge connections goes to which lead on the gauge? Is is as simple as two connections go to the main filament and two go to the degas filament? If that is the case, I could simply hook up a meter to the connections and look for a voltage, or is it more complicated than that? Thanks again.

-Chris

Edit: Well Larry, we will still have to see if I got the better deal, depending if this thing will actually get a reading rather than just powering on. Otherwise I will have bought a 10 dollar paperweight complete with decorative lights and moving needles. =)

[DaveC]

The Ion Collector coax shield should be grounded at the controller end, only. (There's actually no way to ground it at the tube itself, .... except when you have a nude gage... in which all the connections come out through the base connector.)

As to which goes where... on the filament end.... some, if not all of the newer tubes have a symmetric pinout arrangement... meaning that the connector plug can go on either way... makes it nice when you're upside down in a cramped space trying to re-attach the plug.

But... you can almost always trace the connections right through the glass... The grid coil on some tubes is driven to red heat in degas mode, while in other tubes the filament is overdriven a bit to degas by electron bombardment... Personally, I like the grid direct heater mode... saves the filament, and generally creates less contamination from boil-off, and metal evaporation.

Dave Cooper

[kernd]

John

I've been using four pieces of coax cable on my TMP50 with crimp connectors on the end. To be honest, this has worked out fine but is really a PITA when moving the pump. Do you have a better way of going about it?

I was thinking of casting up a connector and making up a four conductor shielded cable with some wire and copper braid. But I'm not sure if I need to worry about crosstalk between phases.

[John Futter]

Dave
The individual wires do not require shielding.
The original cable for the TMP50 was a shielded four core ie three phases and safety earth the shield was connected to another pin on the controller end only.
If you are using a NT10, NT12, NT13 controller then you do need the shield to stop radiating noise from the controller.
As for distance I have used 10 foot cables on the units with no ill effect.

The plug on the bottom of the pump mates with a standard relay type socket from Hirschman I'll edit this post tomorrow at work with the Radio Spares part #. It pays to hold the socket on with the central securing screw which doesn't come with socket .I just cut down a 50mm long 3mm screw to the correct length

[kernd]

John

That's excellent. Thanks a lot.

I'm using a NT12; I only shielded the coax braid on the controller end. You are right the setup is extremely noisy if you don't do this. I'll switch over to a regular 4 conductor shielded cable as you said.

A part number for a mating socket would be awesome. My biggest concern to date has been the thing falling off during a long pump down, especially if only one phase connection came off.

[bpaddock]

> is there anything stopping me from making improvised connections with regular wires?

Look for Oxygen Free medical grade sensor cable.
Try these Medical Device Link sites:

http://www.devicelink.com/
http://www.devicelink.com/mddi/
http://www.devicelink.com/mem/

Far less noisy that most wire.

You'll find lots of Oxygen Free speaker and power cable
crap, which in my view is silly.

[John Futter]

David
link for TMP50 socket

http://newzealand.rs-online.com/web/sea ... m=156-4757

Less than NZ$10