Xylem PC320 Process Controller - Manual (Page 4)

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Both normally open and normally closed relay contacts are provided. Relay
modes include a One Time trigger that will engage a relay one time only for
a programmed on time period when a sensor reading falls outside of a
defined normal range. The Steady state mode will turn on a relay as long as
the sensor reading is out of the normal range. The Cyclic mode will
continually turn a relay on and off for user definable on and off times while
the sensor reading is outside of normal range. Additionally, High Control
and Low Control Modes are provided. These modes are used for maintaining
a sensor reading within a specific range; for example keeping the water level
in a tank between two predefined levels. A sixth mode allows a relay to be
deactivated regardless of settings. There are also programmable Delay
Times and Hysteresis. Setting a Delay Time will delay a relay from turning
on for that amount of time when a sensor reading falls outside of normal
range. This is used to limit the effect of rapidly changing sensor readings
and keeping the relays from reacting quickly to very small changes near a
threshold setting. The Hysteresis function allows the relay to remain on until
the sensor reading falls into the normal range again, plus a defined hysteresis
percentage. This also prevents the relays from overreacting to rapidly
changing events near a threshold level. A test mode is provided for manually
testing relay operation.
A fully scalable 4-20mA output is available for recording sensor data
readings by devices like data loggers, PLC’s, telemetry systems and chart
recorders. There is a factory installed USB data logger option available that
can record these data readings to memory at regular intervals, as well as the
exact times of all changes in relay states and the current sensor reading at that
time. Contact a Sales or Technical Support representative for more
information. To easily interpret this sensor and relay data, a free software
package is available. A separate manual titled “FC220-PC320 Data Logger
Option” describes this in more detail and is available for free download at
globalw.com/support.