Alicat LC Series Liquid Flow Controller User Manual
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Tareing via RS-232 / RS-485 (L-Series only):
Tareing (or zeroing) the flow meter provides it with a reference point for
zero flow. This is a very simple but important step in obtaining accurate
measurements. It is good practice to “zero” the flow meter each time it is
powered up.
If the flow reading varies significantly from zero after an initial tare, give the
unit a minute or so to warm up and re-zero it. If possible, it is helpful to zero
the unit near the expected operating pressure by positively blocking the flow
downstream of the flow meter prior to entering the Tare command. Zeroing the
unit while there is any flow will directly affect the accuracy by providing a false
zero point.
If in doubt about whether the flow is positively blocked, remove it from the line
and positively block both ports before entering the Tare command. If the unit
reads a significant negative value when removed from the line and blocked, it
is a good indication that it was given a false zero. It is better to zero the unit at
atmospheric pressure and a confirmed no flow conditions than to give it a false
zero under line pressure. To send a Tare command via RS-232 / RS-485, enter
the following strings:
In Polling Mode:
Address$$V
Sending a Set-point via RS-232 / RS-485: To send a set-point via RS-232 / RS-485,
“Serial” must be selected under the “Input” list in the control set up mode.
Method 1: Set-point may be set in floating point in serial communication using
serial command (UnitID)SX.YZ
Example: AS4.54 results in Unit ID A changing set-point to 4.54.
Method 2: 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 pressure 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 500 ccm full-scale unit and you wish to apply a
set-point of 125 ccm you would enter the following value:
16000 = (125 ccm X 64000) / Full Scale Flow Range
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:
D16000 followed by “Enter”