Cautionary Notes
Chapter Four: Operation
28
Cautionary Notes
Note 1: Customer Supplied Display Equipment
The controller in the 1152 unit compares its own flow signal with the set point signal, and
positions the valve to reduce this error to zero. Therefore, it is necessary to zero the MFC’s
output, using its zero potentiometer rather than offsetting a non-zero signal with an equal and
opposite signal in the readout equipment if it is so equipped. Failure to properly zero the MFC
will result in a disparity between set point and flow signals equal to the zero offset.
Note 2: MKS Supplied Power Supply/Display Equipment
When the 1152 MFC is used with an MKS Type 147, 246, or 247C, Note 1 does not apply. The
147, 246, or 247C takes the flow signal from the 1152 MFC, zeroes it with the front panel zero
pot, and sends it back to the controller section of the 1152 unit on pin 10 of the Signal (J15)
connector. Refer to Table 3, page 15, for the pinout of the Signal connector (J15).
Note 3: Set Point Command
Use of a set point voltage source of low impedance (<20K ohm) is necessary for concurrence
between set point and flow signal output.
Note 4: Overrange Condition
The 1152 MFC uses an absolute pressure transducer for flow measurement. If the outlet of the
MFC is at ambient (atmospheric) pressure, the pressure transducer will produce a high level
output. It will appear as an overrange condition (Example : 7.5 VDC on a 0 to 5 VDC range).
This may trip safety interlocks that may be present on the process system even though there is no
actual flow through the MFC.
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