DPM-500 Analog Input Meter Instruction Manual
31
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 and/or 4 external relays expansion module. 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
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:
Fail-Safe Operation
The following table indicates
how the relays behave based
on the fail-safe selection for
each relay:
Note: NO = Normally Open,
NC = Normally Closed.
This refers to the
condition of the relay
contacts when the power to the meter is off.
Front Panel LEDs
The LEDs on the front panel provide status indication for the
following:
The meter is supplied with four alarm points that include front
panel LEDs to indicate alarm conditions. This standard feature
is particularly useful for alarm applications that require visual-
only indication. The LEDs are controlled by the set and reset
points programmed by the user. When the display reaches a set point for a high or low alarm, the
corresponding alarm LED will turn on. When the display returns to the reset point the LED will go off. The
front panel LEDs respond differently for latching and non-latching relays.
For non-latching relays, the LED is always off during normal condition and always on during alarm
condition, regardless of the state of the relay (e.g. Relay acknowledged after alarm condition).
For latching relays, the alarm LEDs reflect the status of the relays, regardless of the alarm condition. The
following tables illustrate how the alarm LEDs function in relation to the relays and the acknowledge
button (Default: F3 key assigned to ACK).
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
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
LED
Status
LED
Status
1
Alarm 1
5
Alarm 5
2
Alarm 2
6
Alarm 6
3
Alarm 3
7
Alarm 7
4
Alarm 4
8
Alarm 8
