Ethernet control of Gamma vacuum quad ion pump controller

17 Aug 2021 - tsp
Last update 17 Aug 2021
Reading time 9 mins

Disclaimer / Warning: Please note that this page is in no way associated with Gamma vacuum. Everything here has been discovered while hacking around with their product and might also be totally wrong, only partially complete or inaccurate. It just worked for us.

Introduction

This is a short blog post that describes on how to talk to Gamma vacuum ion pump controllers (in particular their QPC quad pump controller) using Ethernet to query parameters and adjust settings. Particularly we’re using this to monitor the pressure inside a vacuum chamber that has no additional pressure gauge.

There is some official documentation on the used protocol in some manuals - but that’s mainly oriented towards the serial (RS232 or RS485 / modbus) interface. To help ourself with development (and provide some kind of documentation for hacking around later on) I decided to write down our collected - incomplete - information.

Serial port command packet structure

As one can see they applied somehow everything required for a stable serial link though not being the most beautiful ASCII based protocol (I personally do prefer binary protocols so that doesn’t mean much):

This protocol can be used either on RS232 or ModBus - in case of ModBus the configuration of the unit address is crucial. Any malformed packets are simply ignored by the device.

Request packet structure

Length Content Description
1 Byte Start character Always 0x7E
1 Byte Space Always 0x20
2 Byte Address Address of the device on the serial bus (RS485 / Modbus). 2 Hexadecimal ASCII characters.
1 Byte Space Always 0x20
2 Byte Command 2 Hexadecimal ASCII characters
1 Byte Space Always 0x20
optional Data fields Data payload, always terminated by 0x20
2 Byte Checksum Add all fields exclude start, checksum and terminator modulo 256 - simply add and ignore overflow
1 Byte Terminator 0x0D

Response packet structure

Length Content Description
2 Byte Address Address of the remote unit
1 Byte Space Always 0x20
2 Byte Status Literals OK or ER
1 Byte Space Always 0x20
2 Byte Response code 2 Hex characters
1 Byte Space Always 0x20
optional Data fields Data payload, always terminated by 0x20
2 Byte Checksum Add all fields exclude checksum and terminator modulo 256 - simply add and ignore overflow
1 Byte Terminator 0x0D

Ethernet (Telnet) Commands

The documentation for the Telnet protocol is not that good but orients itself at the serial protocol. It misses all of the synchronization patterns (Start character) as well as the checksums - it relies on TCP for that. It’s built around an interactive Telnet-like session without Telnet features. It’s just a TCP connection that shows an greater than sign > with code 0x3E whenever it accepts input. All commands seem to be prefixed by spc - which seems to stand for single pump controller - even for their quad pump controller. This has been the hard part to decode. Despite of this one can use the same commands as over the serial interface:

Command Meaning Sample request Sample response Comments
0x01 Get Model Number spc 01 OK 00 DIGITEL QPC Just some identification for the model
0x02 Get firmware version spc 02 OK 00 FIRMWARE VERSION: 1.38 Identifies the firmware running on the pump controller
0x07 Master reset spc 07 Not tried yet Performs a full software reset
0xFF Legacy master reset spc FF Not tried yet Performs a full software reset
0x91 Set arc detect spc 91 1 YES OK 00 Sets the arc detection mode
0x92 Get arc detect spc 92 1 OK 00 YES Gets the arc detection mode (yes or no)
0x0A Get current spc 0A 1 OK 00 1.4E-06 AMPS Reads the current currently flowing through the pump
0x0B Read pressure spc 0B 1 or spc 0B 2 OK 00 1.6E-08 MBAR Gets the pressure reading calculated from the flowing current
0x0C Read voltage spc 0C 1 OK 00 6970 Gets the current applied voltage in volts (in the sample nearly 7 kV)
0x0D Read supply status spc 0D 1 OK 00 RUNNING 00 or for example OK 00 PUMP ERROR 00 A human readable string that’s also shown on the pump controller itself
0x0E Set pressure units spc 0E M OK 00 Sets the unit to be used for pressure (M is millibars, T is torr, P pascal)
0x11 Get pump size spc 11 1 OK 00 100 L/S Reads the configured pump size.
0x1D Get calibration factor spc 1D 1 OK 00 1.00 Reads the calibration factor for pressure estimation
0x33 Set auto-restart spc 33 1 YES OK 00 Sets auto restart enabled or disabled
0x34 Get auto-restart spc 34 1 OK 00 YES Gets auto restart status
0x37 Start pump spc 37 1 OK 00 Starts the specified pump
0x38 Stop pump spc 38 1 OK 00 Stops the specified pump

Get Model Number (0x01)

The get model number command can be used to identify the type of the ion pump controller.

Get firmware version (0x02)

The get firmware version command identifies the installed firmware.

Since I personally don’t know if this format might change in future my library tries to parse the last argument as MAJOR.MINOR version pair but also keeps the strings - the version is not checked by my personal implementations.

Master reset (0x07, 0xFF)

There are two firmware reset commands available - the legacy one 0xFF does exactly the same thing but is a remaining opcode from some older protocol versions.

Set arc detection (0x91)

This enables or disabled arcing detection of the pump. If arc protection is enabled the ion pump controller reduces the voltage of the pump during arcing. It should usually be enabled.

Get arc detection (0x91)

Tells the status of arc detection (see above for a general description).

Read pressure (0x0B)

Reads pressure of the specified pump. The data field is the index of the pump (for example 1 or 2)

Fetching pressure using Python

I’ve built a small Python module that’s also used by our labs environmental monitoring system to log data (and then visualize using Grafana). This module including an example program is available as a GitHub GIST

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Dipl.-Ing. Thomas Spielauer, Wien (webcomplains389t48957@tspi.at)

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