2-9
SLA7900 Series
Installation and Operation Manual
X-TMF-SLA7900-MFC-eng
Part Number: 541B022AAG
August, 2009
Section 2 Installation
2-11 Operation Check Procedure (Analog I/O)
a.
Mount the MFC in its final orientation.
b.
Apply power to the MFC and allow approximately one hour for the
instrument to warm up and stabilize its temperature.
c.
Do NOT supply gas to the MFC. Ensure that the differential pressure
across the MFC is zero.
d.
Check the MFC zero.
e.
The analog output signal should be equivalent to 0.0 ± 0.2% FS
(0.000 ± 0.010 Vdc). If the zero exceeds one of these limits, follow
the re-zeroing procedure in Section 3-5.
f.
Turn on the gas supply. A positive flow signal may be present due to
valve leak-thru. At 0% setpoint the flow signal output < 0.5% FS.
g.
If flow signal at 0% setpoint is > 0.5%, then there is too much leak
through across valve seat and orifice. MFC would need to be
reworked to adjust valve shutoff.
h.
Supply a setpoint voltage between 1 and 5 Vdc.
i.
Check the MFC analog output signal. The output voltage signal
should match the setpoint voltage (± 20mV) within 10 seconds after
the setpoint is changed.
j. If flow output signal does not match setpoint, and pressure settings
are correct, this could indicate a problem in the MFC. A secondary
issue could be the gas type. When checking with a surrogate gas,
ensure that there is enough pressure to the MFC in order to flow the
correct amount of the surrogate gas.
Example:
Checking an MFC calibrated for 100 sccm SF6 (sulfur hexafluoride). The
sensor factor using N
2
(nitrogen) is 0.27, therefore the equivalent N
2
needed is 100/0.27 = 370.4 sccm. This may require a pressure increase
to make this flow rate.
