Section 4 - Software Design Requirement
Installation and Operation Manual
X-DPT-RS485-GF100-Series-MFC-eng
Part Number: 541B183AAG
March, 2020
Brooks RS485 L-Protocol MFCs
4.5. MFC New Setpoint Conversion
The NewSetpoint request takes values in the range of 0x4000 to 0xC000
which represent set points between 0% and 100% full scale. The linear
relationship between Full Scale set points and NewSetpoint is demonstrated
in the following table:
Full Scale % set point
NewSetpoint Value(Hex)
0.0
4000
25.0
6000
50.0
8000
75.0
A000
99.0
BEB8
100.0
C000
The “NewSetpoint” value may be calculated from the full scale percent
value by:
“NewSetpoint” = (327.68 * full scale %) + 16,384
or
“NewSetpoint” = ((0xC000-0x4000)/100 * full scale %) + 0x4000
Note that at the communication level all values are sent in binary format.
The decimal and hexadecimal formats shown above are for convenience.
•
Other commands that use this scaling are: Filtered Setpoint,
Indicated flow, Sensors Zero, and Sensor Reference Zero
4.6. Sensor Zero Filter
The digital MFC controller should provide sensor zero filter to support
correction for reasonably stable offsets in the gas flow sensor. The actual
flow reading (IndicatedFlow) should be derived by subtracting
SensorCurrentZero
from each sensor measurement.
SensorCurrentZero
can be updated under two conditions, described in the following
sub-sections.
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