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HFM-E-200/HFC-E-202
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2.7.3. Operation with an external sensor. (Fig. 2.2)
In some instances, it might be desirable to use an external sensor to provide process information to the
control circuitry in the flow controller. For example, you might want to control the pressure in a
vacuum system by adjusting the rate at which the system is backfilled with a gas. The new, enhanced
HFC series of flow controllers have provision for accepting a 0-5VDC output from an external sensor at
pin 8 of the “Edge” connector. To activate this feature, the cover of the HFC must be removed to gain
access to PC-888 and move a jumper on JP3. JP3 is a three pin jumper block located just below the
“Edge” connector. In the normal operating mode, the jumper covers the bottom two pins. To select
“External Sensor”, move the jumper to the upper two pins. This swaps the flow input to the controller
circuit from the Flowmeter output to pin 8 of the “Edge” connector.
2.7.4. Soft Start
The response of the control circuit to sudden changes in the Command signal is set at the factory for
fast, stable response and minimal overshoot. If any overshoot is a problem in a particular system, it is
possible to slow down the controller response to sudden Command changes. Remove the outer cover
from the instrument and remove pin jumper JP6 this will insert an R-C filter with a two second time
constant into the command circuit. This will slow down the reaction of the controller to step changes in
the Command signal and will ensure that there is no overshoot or undershoot in actual gas flow.
2.8. Range Changing:
The range of the flow controller can be changed in the field if recalibration facilities are available. The
flow controller may require a different orifice and different laminar Flowmeter element (shunt), which
can be purchased separately from the factory. A listing of the orifices and shunts are available and their
flow rates can be found in Section 4.8.
The range of the small tube shunts can be changes by changing the front disk, consult factory for more
information on disk options.
Figure 2.1