Large Display Temperature Meters
Instruction Manual
43
Front Panel LEDs
Refer to Figure 37 on page 65 for PD755.
Refer to Figure 38 on page 65 for PD756.
Refer to Figure 39 on page 65 for PD757.
The LEDs on the front panel provide status for the following:
LED Status
LED
Status
1
Alarm 1
S
Set point indicator
2 Alarm
2
R
Reset point indicator
3
Alarm 3
4
4 mA indicator
4
Alarm 4
20
20 mA indicator
The Digital Temperature 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 front panel
LEDs are controlled by the set and reset points programmed by the user and the
acknowledge function in latching relay operation. When the display passes a set
point for a particular alarm, that alarm’s LED will light up. When the meter passes
back through that alarm’s reset point the LED will go off if alarm point was set up
for non-latching operation.
Alarm status LEDs respond differently for latching and non-latching relays.
For non-latching relays, LEDs are always off during normal condition and always
on during alarm condition, regardless of state of the relay.
For latching relays, LEDs reflect state 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:
Relay key legend for following tables
Key Relay
condition
On Tripped
Off Reset
Ack Acknowledged
The On and Off keys do not refer to the status of the relay’s coil, which depends
on the fail-safe mode selected.
Non-Latching Relay
Automatic reset only JP5(1-4 off)
Condition LED
Relay
Normal Off
Off
Alarm On
On
Ack (No effect)
On
On
Normal Off
Off
In this application, the meter is set up for automatic reset and non-latching relay.
Acknowledging the alarm while it is present has no effect on either the LED or the
relay. When the alarm finally goes away, the relay automatically resets and the
LED goes off.
