Helios Large Display Strain Gauge Meter Instruction Manual
PD2-6100
40
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 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 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
1
Alarm 1
2
Alarm 2
3
Alarm 3
4
Alarm 4
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