Precision Digital PD6080 - Manual (Page 60)

PD6080/PD6081 Super Snooper Modbus Scanner Instruction Manual
60
Relay Operation Details
Overview
The relay capabilities of the scanner 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, and/or 4 external relays via expansion modules. 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 8 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 8 Pumps
Relays Auto Initialization
When power is applied to the scanner, the front panel LEDs and alarm relays will reflect the state of the
input to the scanner after the first response from the slave device. 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 (failsf)
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 scanner is off.