ProtEX-MAX PD8-7000 Explosion-Proof Temperature Meter Instruction Manual
35
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 alarms, control
applications such as simple on/off temperature control. 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. Relay Alternation 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. 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
