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Serial communication tutorial

Most Alicat instruments equipped with RS-232 or RS-485 serial communications can be communicated with via ASCII commands. The tabs below cover the basics of Alicat’s serial data frame and serial commands. For more details, download the complete Serial Communications Primer.

Note: You can download Alicat’s Serial Terminal Application for command line access to your instruments. This can also be done using a 3rd-party application like PuTTY.

If you are having any problems, check troubleshooting power and communications or contact us.

Video tutorial

Note: Serial commands are not case-sensitive. For simplicity, we assume that the unit ID of the flow controller is A in the listings that follow. <CR> indicates an ASCII carriage return (decimal 13, hexadecimal D).

How to collect data in polling mode

Change the unit ID: A@=[desired unit ID]<CR>
Poll the data frame: A<CR>
Query the data frame format: A??D*<CR>
Query the manufacturer info: A??M*<CR>
Query the current firmware version: AVE<CR>

How to collect data in streaming mode

Begin streaming data: A@=@<CR>
Stop streaming data: @@=[desired unit ID]<CR>
Set streaming interval: AW91=[number of milliseconds]<CR>

How to command a new setpoint (controllers only)

Command new setpoint: as[floating point number]<CR>

How to tare your instrument

Tare the flow rate (flow instruments only): AV<CR>
Tare the gauge pressure (pressure instruments only): AP<CR>
Tare absolute pressure with the barometer (when installed): APC<CR>
Reset the flow totalizer (when installed): AT<CR>

How to change the gas selection (flow instruments only)

Query the list of installed gas calibrations: A??G*<CR>
Select a different gas: AG[Gas Number]<CR>
Create a new COMPOSER gas mix (See instructions here): AGM [Mix Name] [Mix Number] [Gas1 %] [Gas1 Number] [Gas2 %] [Gas2 Number]<CR>
Delete a COMPOSER gas mix: AGD [Mix Number]<CR>

Miscellaneous functions

Hold valve(s) at current position: AHP<CR>
Hold valve(s) closed: AHC<CR>
Exhaust the controller (for dual-valve controllers only: inlet valve closes, exhaust valve opens): AE<CR>
Cancel valve hold: AC<CR>
Lock the front display: AL<CR>
Unlock the front display: AU<CR>

A<CR> (poll the data frame)
AC<CR> (cancel valve hold)
AE<CR> (exhaust for dual-valve controllers: inlet valve closes, exhaust valve opens)
AG[Gas Number]<CR> (select a different gas)
AGD [Gas Number]<CR> (delete a COMPOSER gas mix)
AGM [Mix Name] [Mix Number] [Gas1 %] [Gas1 Number] [Gas2 %] [Gas2 Number]<CR> (create a new COMPOSER gas mix. See instructions here.)
AHC<CR> (hold the valves closed)
AHP<CR> (hold the valves at their current positions)
AL<CR> (lock the front display)
AP<CR> (tare the gauge pressure)
APC<CR> (tare the absolute pressure with the barometer, if installed)
AS[floating point number]<CR> (command new setpoint)
AT<CR> (reset the totalizer, if installed)
AU<CR> (unlock the front display)
AV<CR> (tare the flow rate)
AVE<CR> (query the current firmware version)
AW91=[number of milliseconds] (set streaming interval)
A??D*<CR> (query the data frame format)
A??G*<CR> (query the list of installed gas calibrations)
A??M*<CR> (query the manufacturer info)
A@=[desired unit ID]<CR> (change the unit ID)
A@=@<CR> (begin streaming data)
@@=[desired unit ID]<CR> (stop streaming data)

Standard serial data frame

The following is an example of a typical data frame for a 500 SCCM mass flow controller with optional totalizer:

A +087.6 +025.0 +164.7 +981.6 +985.0 +022741.4 Air HLD MOV TMF

A = device ID (A-Z)
+087.6 = absolute pressure
+025.0 = temperature
+164.7 = volumetric flow rate
+981.6 = mass flow rate
+985.0 = setpoint
+022741.4 = totalized flow since last reset
Air = selected gas
HLD = status code (valve hold)
MOV= status code (mass flow rate overflow)
TMF = status code (flow totalizer missed out of range flow)

Status codes

The following status codes appear both in the serial data frame and on the instrument display:

ADC = analog-digital converter error
EXH = valve exhaust is active (dual-valve controllers only)
HLD = valve hold is active
LCK = front display is locked
MOV= mass flow rate is over the measurable range of the device
OPL = overpressure limit has been exceeded (option)
OVR= flow totalizer rolled over to zero (option)
POV= pressure is over the measurable range of the device
TMF = flow totalizer missed out of range flow (option)
TOV= temperature is over the measurable range of the device
VOV= volumetric flow rate is over the measurable range of the device

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