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140-072011 200/202 Series Page 14 of 24
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 – 5 VDC (or 0 - 10 VDC) output from an
external sensor at pin 13 of the DA-15 (15 Volt), Pin 1 of
the DE-9 (24 Volt) connector. To activate this feature, the
cover of the HFC must be removed to gain access to the
electronics card and move a jumper.
For the 15 Volt units, JP1 is a three pin jumper block
located just below the “D” 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 flow meter output to pin 13 of the “DA-15”
connector.
For the 24 Volt units JP6 is a six pin jumper block located
just to the right of the sensor connector. Pin 1 is in the lower
right corner. There are three jumpers installed horizontally.
The bottom jumper ties the flow output to the valve control
circuit and the middle jumper ties Pin 1 of the DE-9 connector
to reference voltage circuit. Remove both of the lower two
jumpers and reinstall one jumper vertically between the outside
two pins (pins 1 & 3). This will tie Pin 1 of the DE-9
connector to the valve control circuit and allow the controller to
maintain the external process variable equal to the desired
setpoint. The 5 Volt reference is not available in this
configuration.
2.7.4. Response to Command Changes
The response of the control circuit to changes to the command signal is set at the factory for fast, stable
response. If excessive overshoot is present, the response can be slowed removing the jumper labeled
“JP4,” located in the center of PC-828 for the 15 Volt units or by removing the top jumper of JP6 for the
24 Volt boards (located to the right of the sensor connector.
The fastest response to command changes is obtained when JP4/(JP6) is covered by the jumper. This
setup allows large overshoot and undershoot in the actual flow rate while the control circuit is establishing
control at the new command point. A slower response to command changes is obtained when JP4/JP6 is
not covered by a jumper. This setup results in no overshoot or undershoot in the actual flow rate as the
Fi
g
2.2
JP6
Fig 2.3
Normal External
Variable