Edwards Active Pirani Gauge Reading

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Josh Smith
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Edwards Active Pirani Gauge Reading

Post by Josh Smith » Thu Feb 22, 2018 4:06 pm

Hello All,
I recently bought a NW-16 Edwards Active Pirani Gauge for reading vacuum levels to the milliTorr levels. I'm running into some issues regarding utilizing it with an RJ45 jack to be able to log data on my computer. Since you need to read/send voltage on a pin by pin basis, I was thinking of stripping the RJ45 cable and hooking it up to an Arduino in order to manipulate the cable on the pin-pin basis that's required. I know it takes a higher voltage than the arduino to be able to operate, so I'll turn that on with a separate switch, all I want to do with the arduino is to be able to read the variable voltage output to get the pressure reading. Does this sound like a good idea, or do you guys think there might be better ways of going around this?
Thanks for your time,
Josh

Rex Allers
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Re: Edwards Active Pirani Gauge Reading

Post by Rex Allers » Fri Feb 23, 2018 3:20 am

I have no direct experience with this gauge but I found the manual and took a quick look at it. I'll give a brief comment.

First, your description of manipulating the cable on a pin-by-pin basis sounds rather odd to me. Obviously, to use the device, you need to connect the device to circuits that can power it up and read the signal output. It looks like you could do that with a minimum of 4 wires on pins 1, 2, 3 & 5. How you get wires from the RJ45 plug to your circuits is up to you.

Seems the output on 3 & 5 is an analog voltage in the range of 2 to 10 V, where 10 = atmospheric pressure.

If you haven't used it before, I would start with just applying power, in the needed 20 - 36 V range, on 1 & 2 and measuring the output with a voltmeter across 3 & 5. Connect it to a vacuum and see that the output voltage varies with pressure.

If you then want to use an Arduino, you'll need to consider that the max input for the ADC is limited to the supply of the microprocessor, which is 3.3 or 5 V depending on the flavor of Arduino you are using. So you'll need to put the sensor's output through a divider or alternately clamp (limit) the input to the high rail of the arduino. Should be OK but you need a little electronics knowledge for the input circuit. Then of course, enough knowledge to write or adapt the software to read the voltage and do something with the result.

Looks like the interesting pressure range for an operating fusor would give outputs in about the 2 to 5 V range. That varies some depending on whether the gauge is version M or L; you didn't say. This might give you max resolution if you use a 5 V arduino and clamp the input so it can't go above 5 V. You'll get about half that resolution if you divide the input voltage so that 10V from the sensor gives 5V into the ADC pin.

So, just a few basic thoughts. Hope it is a little help.
Rex Allers

Jerry Biehler
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Re: Edwards Active Pirani Gauge Reading

Post by Jerry Biehler » Sat Feb 24, 2018 6:05 am

Yeah, all you need to do us use a voltage divider to read the analog output and then you have to do the math in software to decode the analog signal since it is a log/lin representation of the pressure. I have done this with pfeiffer gauges and it is not too hard.

Josh Smith
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Re: Edwards Active Pirani Gauge Reading

Post by Josh Smith » Sun Feb 25, 2018 3:16 pm

It’s an L Gauge. I did what you guys suggested; I put together 3 new 9V batteries in a series and they produce around ~28 V, and connected them to pins 1 and 2. However, after hooking up the multimeter to pins 3 and 5, the output only goes to 400 mV and then resets and slowly goes back up, process repeating. I did some messing around with the potentiometers for the set-point, and the output doesn’t reset anymore, however it idles at around 390 mV and when I use my vacuum pump it’s a bit erratic, but the general trend is downwards as the pressure decreases, but at a rate of around ~1.5V/min. The manual says if the voltage is in the error range, then there’s an issue with the electrical input or that pin 7 is connected to 2 or ground, however I tested the case for both of these and the power input worked fine and the pins were all cut; so I’m guessing the gauge is faulty. I might just cut my losses and get an NPT-Thermistor type gauge off amazon, as I have an adaptor for that type and I’ll try to record data off of that one.
Thanks -Josh

Josh Smith
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Re: Edwards Active Pirani Gauge Reading

Post by Josh Smith » Sun Feb 25, 2018 6:57 pm

Nevermind, I might be the clumsiest person on this planet. I used the wrong pin layout for the RJ45 cable, which is why nothing would work. After fixing it, everything worked and I was able to calibrate it successfully. Then, I was able to pump down the system to around 4V, which the table says is about 16 microns, after a few minutes with the Pfeiffer Duo 1.5A pump. Big thanks for the help, guys :)
pressure readout.jpg

John Futter
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Re: Edwards Active Pirani Gauge Reading

Post by John Futter » Mon Feb 26, 2018 5:54 am

Josh
More haste less speed

You are extremely lucky that you did not damage the gaugehead by wrong connections

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