Fusor Forums

Hi Guys,

Do any of you have experience with this vacuum gauge. I just received one of these pirani gauges with the panel meter, bought on ebay. It looks nice and clean, and powers up, but when I connect the meter to the gauge, with an RJ45 cable at atmospheric pressure, the meter swings out to full vacuum.

Any suggestions appreciated...

Steven

I have the APG-MP version (Pt/Rh filament, rather than your Au/W, but yours reads to a lower pressure). I can't say I have seen that it reads 'vacuum' at start-up (though I don't have the 'meter' part - it is an active gauge and you can 'read' the gauge without it). Doesn't it mean it is high resistance on the filament? (Mine was an ebay 'song'; an unused item still in cal, for £10! )

You can check it without the readout, in case that part is the faulty part. You just put 20V on the right lines of the RJ45 connector, and 'enable' one of the lines by tying to ground, and read off a 1-10V signal. I can dig out the manual/connections for reading the gauge that way, if you want to try that first. Would it be a good idea to run it whilst under vacuum, so as to give the filament a chance to burn off any contaminants on it?

Thanks Chris,

I will give that a try...

Steven

Steven,

Please excuse a dumb question.
When you say "the meter swings out to full vacuum", do you mean the left end of the scale, as shown in your picture? Is it even farther to the left when power is off?
That would be consistent with the scale on old nonlinear Convectron (tm) analog displays:
* Power off position (0 volts)
* Full vacuum position (0.375 volts)
* Intermediate decades on scale
* 760 torr position (5.xx volts).

If it really does move to the full vacuum position, not the 1-atmosphere position, then I would open the case, look for obvious opens or shorts, then try to probe voltages on the sensor tube pins. Could you use a Convectron manual with schematic diagram?

Rich, I believe the dial really is *just* a glorified voltmeter (and power source for the gauge). The gauge does all the work!