ProtEX-MAX PD8-6060 Explosion-Proof Dual-Input Meter Instruction Manual
39
Relay Operation Details
Overview
The relay 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 internal relays. Typical applications include high or low temperature, level, pressure or flow
alarms, control applications such as simple on/off pump control, and pump alternation control for up to 4
pumps. There are four basic ways the relays can be used:
1. High or Low Alarms with Latching or Non-Latching Relays
2. Simple On/Off Control with 100% Adjustable Deadband
3. Sampling (Based on Time)
4. Pump Alternation Control for up to 4 Pumps
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. The following table indicates how the alarm LEDs and relays will react on power-up
based on the set and reset points:
Alarm #
HI or LO
Alarm
Set Point
Reset
Point
Power-Up
Reading
Relay &
LED
1
HI
1000
500
499
Off
2
LO
700
900
499
On
3
LO
250
400
499
Off
4
HI
450
200
499
On
Fail-Safe Operation
The following table indicates how the relays behave based on the fail-safe selection for each relay:
Fail-Safe
Selection
Non-Alarm State
Alarm State
Power Failure
NO
NC
NO
NC
Off
Open
Closed
Closed
Open
Relays go to
non-alarm state
On
Closed Open
Open
Closed Relays go to
alarm state
Note: NO = Normally Open, NC = Normally Closed. This refers to the condition of the relay contacts when
the power to the meter is off.
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