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For example, suppose a controller with unit ID A was ordered with units of
SCFM or the “device units” are currently selected as SCFM. If air is selected and
the setpoint value is set to 2.004 SCFM, at atmospheric temperature, the data
frame may read:
A
+014.70 +025.00 +02.004
+02.004
2.004
Air
Unit ID Pressure
Temp
Vol. Flow Mass Flow Setpoint
Gas
MC-Series Mass Flow Controller Data Format
On units with the totalizer function, the totalized flow will be displayed in column
seven, with the selected gas moving to column eight. Additional columns,
including status codes, may be present to the right of the gas selection column.
Changing the gas selection using Gas Select via RS-232 / RS-485
To change the selected gas, type
(unit ID)G(gas number)<CR>
. For
a complete list of gas numbers available on the device, see “Gas Lists with
Viscosities, Densities and Compressibilities” in this manual. This list is also
available on the gas select menu on the unit. For example, Helium has a gas
number of 7. To change the selected gas on unit “A” to Helium, type
AG7<CR>
.
Sending a Setpoint via RS-232 / RS-485
To send a setpoint via RS-232 / RS-485, serial communication must be selected
under the “Setpt Source” list in the control set up menu.
Method 1: Setpoint may be set as a floating point number in serial
communication using the setpoint command
(unit ID)S(floating
point number)<CR>
. For example,
AS4.54<CR>
changes the setpoint for
unit “A” to 4.54 in the current device units.
Method 2: The setpoint can also be set in reference to a portion of the full
scale. Type
(unit ID)(integer)<CR>
. Values between 0 and 64000 are
acceptable, which correspond linearly to 0 and 100% full scale flow respectively.
Once a setpoint is accepted, the data frame will be returned with the setpoint
column changed accordingly. If no change is observed, make sure that “Analog”
is not the selected “Setpt Source” in the Control Setup menu.
The formula for performing linear interpolation is as follows:
Value = (desired setpoint) X 64000 / (full Scale)
For example, when changing the setpoint on a 100 SLPM full scale controller to
35 SLPM, the following value should be entered:
22400 = (35 SLPM) X 64000 / (100 SLPM)
Sending a Setpoint to a Bidirectional Controller via RS-232 / RS-485
For a bidirectional controller, the setpoint command may be sent in either of
the above two methods with the following changes:
Using Method 1, a negative setpoint may be set using a negative sign in the
command. For example,
AS-4.54<CR>
changes the setpoint for units “A” to
-4.54 in the current device units.
