MKS 1579A, Инструкция по эксплуатации

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Chapter 5: Operation (Analog Units) 1579A/579A
36
Zero Adjust
1. If no gas is flowing and the mass flow controller has stabilized (ref. to Appendix A,
Specifications, Warm Up) the flow output signal can be zeroed. This can be done in two
different ways:
a) using the push button AUTOZERO, located at the gas inlet side of the unit. Use this
means only when gas flow is completely stopped. Check that the flow signal has been
set to zero!
or
b) using the potentiometer ZERO, located at the gas inlet side of the unit.
The potentiometer allows to adjust the zero signal to a known value of leak flow if
completely shut off is not possible.
2. When using a control unit by MKS then you should use the zeroing means there. If the
control unit does not provide enough compensation range then the potentiometer ZERO at
the mass flow unit must be used.
Note
Zeroing should be done only on units that are installed in final position.
It is recommended to completely stop the gas flow prior to any zero
adjustment.
If a pressure difference exists at the mass flow control unit then a small
flow might occur even if the integrated control valve is closed. This is
more likely with special units for low inlet pressures.
Do not adjust the flow signal then to zero because it is a real flow but
use a positive shutoff valve to definitely stop the flow.
The integrated control valve may not completely shut off the gas flow.
3. Periodically check the zero adjustment of the unit, e.g. on maintenance intervals. The zero
adjustment is mainly affected by thermal effects and especially by contamination.
Beside the need for achieving measurements of highest accuracy the zero signal is a very
important indication for diagnosing the condition of flow sensor and control valve.