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3 SPECIFICATIONS
3.2.8 Output off-time current error detection function (available for Q64TCTTBW and
Q64TCRTBW only)
3.2.9 Loop disconnection detection function
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Example 2: The difference from the standard current at each station is: Channel
1: -16%, Channel 2: -17%, Channel 3: -22%, Channel 4: -19%, the compensation
value becomes -16%.
The heater disconnection detection is performed from the values after a -16%
compensation: Channel 1: 0%, Channel 2: -1%, Channel 3: -6%, Channel 4: -3%.
Thus, when the heater disconnection detection setting value is at 80%, none of
the channels are detected as disconnected.
Heater
disconnection
Channel No.
detection setting
value
1
2
80%
3
4
(c) Restrictions
• The heater-disconnection compensation function will not work if only one
channel is used.
• The heater-disconnection compensation function will not work if only one
channel is used to keep the heater on while the others are used to keep it
off.
The module may detect a disconnection even when the heater is not
disconnected.
• The heater disconnection detection compensation value is up to 20%.
Therefore, when there is a voltage drop by more than 40%, a disconnection
is detected even with a 20% compensation.
(1) Using the reference heater current value (load current value detected by the
current sensor (CT)), this function checks for a transistor output off-time current
error when the transistor output is off.
(2) The transistor output off-time current error detection function compares the
reference heater current value and the current value of the heater disconnection
alert, and judges it as an output off-time current error if the reference heater current
value is higher than the current value of the output off-time current alert.
Note that output off-time current error detection will not be made if the transistor
output off period is within 0.5 seconds.
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.
When the PID operation value has reached 100% or 0%, this function starts monitoring
the variation of the process value per loop disconnection detection judgment time to
detect a heater or input disconnection.
(1) When the heater is disconnected, when the input is disconnected or shorted, or
when the external operation device contact does not turn on, it is judged as an
error since the temperature will not rise despite the control output provided.
In this case, an alert is output if a temperature rise of 2°C or more is not observed
within the preset loop disconnection detection judgment time after the control
output is provided 100%.
Difference from the
Compensation
standard current
value
-16%
-17%
-16%
-22%
-19%
MELSEC-Q
Difference from the
standard current
Disconnected
after compensation
0
No
-1%
No
-6%
No
-3%
No
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