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HFM-E-200/HFC-E-202
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4.3.2. Miscellaneous adjustments
Periodically, during normal operation, the ZERO should be checked and adjusted when required. If the
instrument is not stopping the flow completely when command signal is Zero, the orifice may require
turning approximately 1/8 turn clockwise.
4.4. Inlet Removal:
The fitting on the inlet side must be removed to gain access to the filter or shunt assembly. First shut off
the supply of gas to the instrument. Disconnect the Swagelok fitting on the inlet and outlet sides of the
transducer, and remove it from the system plumbing. Carefully remove the inlet fitting, spring (if
present) and shunt, noting their order and proper orientation. The shunt can be severely damaged if
dropped. Examine the filter and shunt. If either is dirty or blocked, clean or replace as applicable.
Reassembly is the reverse of the removal procedure. Recalibration of the HFC is necessary.
4.5. Printed Circuit Board Replacement
In the unlikely event that the PC board fails, it is easily removed from the instrument and replaced with
a spare to minimize instrument downtime. Replacement of the PC board will require the instrument to
be recalibrated per Section 4.3.1.
Unplug the power cable from the top of the transducer. Remove the two jackscrews next to the “Edge”
connector and the two screws on the sides of the cover. Lift off the cover and unplug the four-wire
sensor plug and the two wire valve plug, noting their orientation prior to removal.
Remove the screw that holds the PC board to the sensor. Troubleshoot or replace as applicable.
Installation is the reverse of the above procedure. Recalibrate if any components were changed or if any
potentiometers were adjusted.
4.6. Sensor Replacement:
If the sensor fails or becomes plugged it can be removed. Remove the cover and the PC board per
Section 4.5 above. Remove the three bolts holding the sensor to the instrument base. Remove the
sensor from the base noting the two O-rings (Parker 2-005, V884-75) between the sensor and the base. If
the sensor is plugged it can be cleaned by running a fine wire (approximately 0.008" diameter) through
the tube. If sensor needs replacement, obtain another from the factory and install it. Ensure that O-
rings are clean and intact. Install O-rings on seating surface, then carefully place sensor over O-rings
and tighten down the three screws evenly. Replacement of sensor will require recalibration per Section
4.3.1.
4.7. Orifice Changes:
The orifice may require replacement if a flow range change is desired, if a large change in differential
pressures across the valve is desired or in the event that a small orifice becomes plugged. Replacement
orifices can be acquired from the factory. See Section 4.8 for the list of standard orifices and their flow
rates in air.
When using nonstandard pressures or gases that have specific gravities different than air (such as
hydrogen or helium), the diameter of the orifice must be calculated using the following procedure:
A) Determine the minimum expected upstream pressure (Pu) in PSI absolute and the maximum
expected downstream pressure (Pd) in PSI absolute for full flow conditions.
B) If Pu >2Pd, use formula 1; otherwise use formula 2.