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Serial Communications
Commanding a New Setpoint Serially
Before attempting to send setpoints to your mass ow controller serially,
conrm that its setpoint source is set to Serial/Front Panel by selecting MENU >
CONTROL > ADV CONTROL > SETPT SOURCE.
There are two ways to command a new setpoint over a serial connection, as
described below. In either of these methods, the data frame returns the new
setpoint value when it has been accepted as a valid setpoint.
Sending Serial Setpoints as Floating Point Numbers
In this method, you send the desired setpoint value as a oating point
number:
Command new setpoint: as[setpoint as oating point number]<CR>
Example: as15.44<CR> (setpoint of +15.44 slpm)
When using a bidirectional mass ow controller, negative setpoints are sent
by adding the minus sign (-):
Example: as-15.44<CR> (setpoint of -15.44 slpm)
Sending Serial Setpoints as Integers in Reference to Full Scale
In this method, your controller's full scale range is represented by a value of
64000, and a zero setpoint is represented by 0. To calculate your intended
setpoint, use the following formula:
Integer value = 64000 x [desired setpoint] / [device full scale]
A desired setpoint of +15.44 slpm on a 20-slpm mass ow controller is
calculated as 64000 x 15.44 / 20.00 = 49408. The command to assign the
setpoint based on this integer value is:
Command new setpoint: a[setpoint as integer where 64000 is full scale]<CR>
Example: a49408<CR> (setpoint of 15.44 slpm)
When using a bidirectional mass ow controller, 0 represents -100% of full
scale, 32000 represents 0, and 64000 represents +100% of full scale. Use the
following formule to calculate the integer value:
Integer value = 64000 x [desired setpoint + full scale] / [device full scale x 2]
A desired setpoint of +15.44 slpm on a 20-slpm bidirectional mass ow
controller is calculated as 64000 x (15.44 + 20.00) / 40.00 = 56704. A desired
setpoint of -15.44 slpm on the same mass ow controller is calculated as
64000 x (-15.44 + 20.00) / 40.00 = 7296.