3. While running process gas at the normal operating pressure, close the down stream
isolation valve.
4. Place the MFC in purge mode or give it a command to flow 100% setpoint. Monitor the
indicated flow until it stabilizes near zero.
5. Close the upstr
eam isolation valve.
6. Give the MFC a zero percent flow command to close the control valve.
7. Let the MFC warm up and stabilize for 60 minutes.
8. Monitor the zero output to insure it has stabilized.
9. ANALOG MFC’s - Adjust R13, Zero Potentiometer until desired zero value is
established.
10. DIGITAL MFC’s - Activate the zero adjust routine by one of two methods:
10.1 Depress the zero momentary contact switch on the top of
the MFC.
10.2 Through the RS 485 digital interface: Class0x68, Instance
1, Attribute 0xBA. Send a write command with an 8 bit
integer value of 1.
11. Wait 30 seconds while the MFC runs the zero routine. Do not send any commands to
the MFC or disturb the inlet pressure.
Note: The status of the zero service routine can be monitored through the RS485
digital interface. Read the Class 0x68, Instance 1, Attribute 0xBA. The MFC
will return an eight bit integer value of 1 while it is in process of running the zero
ser
vice r
outine and r
etur
n an eight bit integer value of 0 when the zero service
routine has been completed.
12. Read the zer
o output. If it is not 0% FS +/- .05%, then r
epeat fr
om step 9.
16.2.5
Conclusion
Improperly zeroed MFCs can cause significant calibration errors and result in process
inconsistencies. Following the above zeroing procedure should eliminate the most often
overlooked sources of zero adjustment error. If you have any questions regarding the
adjustment of MFC zer
o or any technical questions, please call the Celerity Applications
Engineering Department at (714) 921-2640 or visit our website at www.celerity.net.
19
©2005 Celerity
, Inc.
#199-001-0006 REV
.F 4/05
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
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