Interfacing with an old Edwards Vacuum Gauge (AGD) *WIP*

Of interest on this gauge are Relays that flip when the vacuum hits a Set Point, as well as a Chart Recorder port.

TODO: Put code on GitHub, post here.

The Set Point Relay

  • Rated for 250Vac @ 3A 1

There are two relays, one for each Gauge you can connect to this AGD.
Each relay has three Screw Terminals:

  • Normally Closed (N/C) - which is connected to Common before the Set Point is reached,
  • Common - which is what is being switched, and
  • Normally Open (N/O) - which connects to Common when the Set Point is reached.

Using this we can detect states surrounding the Set Point. With an Arduino we can connect N/C and N/O to Digital Pins, set as INPUT_PULLUP, and the Common to Ground.

The Chart Recorder Port

The Chart (recorder) port is of great interest to me, as far as interfacing to the device to get vacuum measurements into a microcontroller.

Here are some quick details on it:

  • Max Load: 10kOhms
  • Max Current Source: 1mA
  • It is a 5-Pin, 180° DIN connector, female 2
  • The outputs for the vacuum are 2-10V 3 1
  • Though other sources report a max of 12v [^source], and I have seen voltages higher than 10v
  • The voltage starts high (no vacuum) and goes down as the pressure drops (vacuum increases)
  • The voltage is linear when it comes to the gauge needle movement, but the card insert with the measurements are not

AGD General

AGD Stands for Active Gauge Display

APG General

  • APG stands for Active Pirani Gauge
  • The insert card in the AGD I have is "Gauge type: APG-M"

AGD Links

APG-M Head/Controller Links

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