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4.4.7 Sensor Break Alarm, Sbr
A sensor break alarm occurs if the sensor or its connections to the sensor input become
open circuit or greater than a high impedance, see section 5.2.14.1.
It can be configured using ‘P’ code P35 as follows:-
Piccolo Range
☺
P codes are found
in section 5.2.
On This is the default state. In operator levels 1 and 2, Sbr will flash in the display if the sensor is open circuit.
LAt Latching If an open circuit input occurs the alarm will be latched until acknowledged.
The alarm will only reset after it has been repaired. It behaves the same as a latched
alarm configured as Nan (Manual).
oFF No sensor break alarm An open circuit input will not be detected.
A sensor break alarm can operate independently of other alarms.
4.4.8 Sensor Break Safe Output Demand
If a sensor break alarm occurs S.br is displayed and the output from the controller will adopt a ‘Safe’ level. This is
set using ‘P’ code P36. The default is 0% which means that all control outputs are off. For a heat/cool controller the
full range is -100% to +100%. It is not limited by the Output High and Low limits set in Operator Level 2. The level
set must be chosen with care to make sure that the process does not over heat or over cool. It may, however, be
useful to maintain a small amount of power to keep the process at a ‘standby’ temperature if the input sensor fails.
If the controller is in MAN mode (Auto/Manual = Man) S.br is displayed, but the output power does not adopt the
Safe value but will adopt the manually set level.
If the controller is in standby mode (Auto/Manual = OFF) S.br will be displayed and the outputs will always go to off
(0%).
4.4.9 Loop Break Alarm, L.br
The loop break alarm attempts to detect loss of restoring action in the control loop by checking the control output,
the process value and its rate of change.
The loop is considered to be broken if the PV does not respond to a change in the output in a set amount of time.
Since the time of response will vary from process to process the Loop Break Alarm Time parameter P34 allows a
time to be set before an alarm is initiated. For a PID controller, if the PV has not moved by 0.5 x Pb (Proportional
Band) in the loop break time the loop is considered to be in break. The loop break time is set automatically
following an Auto-tune, a typical value is 12 x Td (Derivative Time). For an On/Off controller Loop Break Time is not
shown and loop break alarm is inhibited. When a loop break is detected the output power will drive to high or low
limit.
If a loop break alarm occurs the ALM beacon flashes together with the message L.br and OP3 (default) or any other
output attached to the Loop Break Alarm operates.
If the PV then changes showing that the loop is responding, the loop break alarm condition disappears.
Acknowledgement of the loop break alarm sets the ALM beacon to constant if the alarm is still present – the L.br
message continues to flash and the output remains active.
Loop break detection works for all control algorithms, PID and ON-OFF.
See also ‘P’ code P34 further information.
4.4.10 Current (CT) Alarms
If the load current is being measured using the Current Transformer option, there are three alarm types available:-
Mnemonic Name Alarm Message Displayed
Ld.AL Load Current Alarm Setpoint Ct.Ld
LE.AL Leakage Current Alarm Setpoint Ct.Le
Hc.AL Overcurrent Alarm Setpoint Ct.Hc
The threshold levels for these alarms are set in Level 2.
28 Part No HA031260 Issue 1 May -12