Alicat VC Series Volumetric Flow Controller User Manual

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Once you have established communication with the unit and have a stream of information filling your

screen:

Type *@=A followed by “Enter” (or using the RS-232 communcation select menu, select A as identifier

and exit the screen) to stop the streaming mode of information. Note that the flow of information will

not stop while you are typing and you will not be able to read what you have typed. Also, the unit

does not accept a backspace or delete in the line so it must be typed correctly. If in doubt, simply hit

enter and start again. If the unit does not get exactly what it is expecting, it will ignore it. If the line

has been typed correctly, the data will stop.
You may now poll the unit by typing A followed by “Enter”. This does an instantaneous poll of unit

A and returns the values once. You may type A “Enter” as many times as you like. Alternately you

could resume streaming mode by typing *@=@ followed by “Enter”. Repeat step 1 to remove the

unit from the streaming mode.
To assign the unit a new address, type *@=New Address, e.g. *@=B. Care should be taken not to

assign an address to a unit if more than one unit is on the RS232 line as all of the addresses will be

reassigned. Instead, each should be individually attached to the RS-232 line, given an address, and

taken off. After each unit has been given a unique address, they can all be put back on the same

line and polled individually.

Sending a Set-point via RS-232: To send a set-point via RS-232, “Serial” must be selected under

the “Input” list in the control set up mode. To give controllers a set-point, or change an existing point,

simply type in a number between 0 and 65535 (2% over range), where 64000 denotes full-scale flow

rate, and hit “Enter”. The set-point column and flow rates should change accordingly. If they do not,

try hitting “Enter” a couple of times and repeating your command. The formula for performing a linear

interpolation is as follows:

Value = (Desired Set-point X 64000) / Full Scale Flow Range

For example, if your device is a 100 SLPM full-scale unit and you wish to apply a set-point of 35 SLPM

you would enter the following value:

22400 = (35 SLPM X 64000) / 100 SLPM

If the controller is in polling mode as described in Changing from Streaming Mode to Polling Mode, the

set-point must be preceded by the address of the controller. For example, if your controller has been

given an address of D, the set-point above would be sent by typing:

D22400 followed by “Enter”

To adjust the Proportional and Differential (P&D) terms via RS-232:
Type *@=A followed by “Enter” to stop the streaming mode of information.
To adjust the “P” or proportional term of the PID controller, type *R21 followed by “Enter”.