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MELSEC-Q
3 SPECIFICATIONS
3.2.8 Loop disconnection detection function
The loop disconnection detection function detects errors in the control system
(control loop) caused by a load (heater) disconnection, external operation device
(e.g. magnetic relay) fault, input disconnection and others.
The execution of the loop disconnection detection is performed with the setting of
loop disconnection detection judgment time (buffer memory address: 59, 91).
When the manipulated value has reached 100% or 0%, this function starts
monitoring the variation of the measured value per loop disconnection detection
judgment time and detects errors in the control loop. *1
If the following variation has not been seen within the set loop disconnection
detection judgment time, the corresponding bit (b13) of alert occurrence description
(buffer memory address: 5, 6) becomes 1, and ALM LED flickers, and it is output as
an alert.
If an alert occurs during control, the control continues its operation. Output doesn't
turn off.
The variation ranges of the measured value of loop disconnection detection
judgment are 2
for thermocouple input and 0.2% for micro voltage, voltage and
current.
The loop disconnection detection judgment function will be an alert status in the
following cases.
(1) When the manipulated value has reached 0%
Forward operation: The measured value does not increase over the variation
range within loop disconnection detection judgment time.
Reverse operation: The measured value does not decrease over the variation
range within loop disconnection detection judgment time.
(2) When the manipulated value has reached 100%
Forward operation: The measured value does not decrease over the variation
range within loop disconnection detection judgment time.
Reverse operation: The measured value does not increase over the variation
range within loop disconnection detection judgment time.
*1: In the manual control mode, when the manipulated value is not 0% or
100%, the loop disconnection detection cannot be performed.
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