Xylem PC320 Process Controller - Manual (Page 8)

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V. Sensor Input
The PC320 accepts any analog sensor with a 4-20mA, 0-5VDC or 0-1VDC output.
Available power for the sensor depends on the power input to the PC320. When
powering the PC320 from 12 volts, the sensor power is also 12 volts. If you are
running from a power supply of 18-24 volts, the sensor power can be selected from
either a regulated 12 volt supply, or directly from the 18-24 volt input. The power can
also be connected continuously or it can be set to be turned on and off by the PC320
when using a power saving mode. In this mode the sensor is turned on at user defined
intervals for a programmable warm-up time, then turned off again to conserve power.
VI. 4-20mA Output
A 4-20mA output is provided that is proportional to any defined sensor range. This
allows the data history to be recorded by an external data logger or PLC, or by the
internal data logger option, or both. The output is fully scalable and allows the user to
select the sensor ranges that are proportional to the 4mA and 20mA output currents.
VII. Relay Operation
Several settings independently control the operation of the 4 relays. These settings are
Upper Threshold, Lower Threshold, Hysteresis, Delay Time, Relay Mode, On Time
and Off Time. Not all of these settings may apply depending on which relay mode is
selected.
The Upper and Lower Threshold settings establish a normal band which the sensor
reading should remain in. If a sensor reading rises above the Upper Threshold, the
relay will trigger. Likewise; if the sensor reading falls below the Lower Threshold, the
relay will also trigger. If either the Upper or Lower Thresholds are not needed, they
should be set to a value outside of the sensor output.
Example: A water level sensor has a range of zero to 15 feet and is installed in a water
tank to control a pump. Relay 1 has an Upper Threshold of 10 feet and a Lower
Threshold of 5 feet. The relay may trigger (depending on mode) when the water level
rises above 10 feet or falls below 5 feet. If it is desired for the relay to turn on only
when the level is above 10 feet, but not below 5 feet; change the Lower Threshold to a
value outside of the normal range of the sensor, like a negative number (-10 feet).