Model PD655 Large Display Process Meter
Instruction Manual
72
Relays Operation
Overview
The Relays capabilities of the meter expand its usefulness beyond simple
indication to provide users with alarm and control functions. These capabilities
include front panel alarm status LEDs as well as either 2 or 4 optional relays.
Typical applications include high or low temperature, level, pressure or flow
alarms, simple control applications like sump-pump or tank-filling and automatic
or manual batch controlling. There are four basic ways the relays can be used:
1. High or Low Alarms
2. Simple On/Off Control with 100% Adjustable Deadband
3. Automatic Batch Control
4. Manual
Batch
Control
Relays Auto Initialization
When power is applied to the meter, the front panel LEDs and alarm relays will
reflect the state of the input to the meter. For instance, if the meter is powered up
and reads 500, the following table indicates how the alarm LEDs and relays will
react based on the various set and reset points:
Alarm #
HI or LO
Set
Point
Reset
Point
Power-up
Reading
Relay &
LED
1 HI
1000
500
499
Off
2 LO
700
900
500
On
3 LO
250
400
500
Off
4 HI
450
200
500
On
Fail-Safe Operation
The following table indicates how the relays behave based on Jumper J5 being
installed or not installed:
Jumper J5 on
Options Board
Fail-Safe
Relay Coils
Energized in
Power Failure
On
Enabled
Non-alarm state
Relays go to
alarm state
Off
Disabled
Alarm state
Relays go to
non-alarm state
