Helios PD2-6080/PD2-6081 Modbus
®
Scanners
Instruction Manual
46
Relay Action for Loss of 4-20 mA
Input (Loop Break)
The loop break feature is associated with the 4-20 mA
input. Each relay may be programmed to go to one of
the above conditions when the scanner detects the
loss of the input signal (i.e. < 0.005 mA).
Notes:
1. This is not dependent on the
Communications Break or Response
Timeout setting.
2. This is not a true loop break condition; if the
signal drops below 0.005 mA, it is interpreted
as a “loop break” condition.
The following graph shows the loop break relay
operation for a high alarm relay.
When the scanner detects a break in the 4-20 mA
loop, the relay will go to one of the following selected
actions:
1. Turn
On
(Go to alarm condition)
2. Turn
Off
(Go to non-alarm condition)
3.
Ignore (Processed as a low signal condition)
Note: Select no Action
Time Delay Operation
The following graphs show the operation of the time
delay function.
When the signal crosses the set point, the
On
time
delay timer starts and the relay trips when the time
delay has elapsed. If the signal drops below the set
point (high alarm) before the time delay has elapsed,
the
On
time delay timer resets and the relay does not
change state. The same principle applies to the
Off
time delay.
Note: If
“
Automatic or Manual
(
A-nmAn
)”
reset mode
is selected, the LED follows the reset point and not
the relay state when the relay is acknowledged.
Relay Sampling Operation
When the signal crosses the set point, the relay trips
and the sample time starts. After the sample time has
elapsed, the relay resets. The cycle repeats every
time the set point is crossed, going up for high alarms
and going down for low alarms.
The sample time can be programmed between 0.1
and 5999.9 seconds.
