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CHAPTER 4 FUNCTIONS
4
4.22 Loop Disconnection Detection Function
4.22 Loop Disconnection Detection Function
Using this function detects an error occurring within a control system (control loop) due to reasons such as a load
(heater) disconnection, an externally-operable device (such as a magnetic relay) failure, and input disconnection.
(1) How an error is detected
From the point where the control output has reached upper limit output limiter value or lower limit output limiter
value, the amount of changes in the temperature process value (PV) is monitored every unit time set and
disconnection of a heater and input is detected.
(2) Examples of the errors detected
The following are the examples of the errors detected.
(a) When control output is being performed
The Q64TCN detects an error because the temperature does not rise even when control output is being
performed under the following conditions:
• When a heater is disconnected
• When input is disconnected or short-circuited
• When the contact point of an externally-operable device does not turn on
After the control output has reached upper limit output limiter value, if the temperature does not rise by 2°C
( ) or more within the loop disconnection detection judgment time set, an alert is output. (The operation is
reversed for forward action. ( Page 252, Section 4.21))
(b) When control output is not being performed
The Q64TCN detects an error because the temperature rises even when control output is not being performed
under the following conditions:
• When input is disconnected
• When the contact point of an externally-operable device was bonded
After the control output has reached lower limit output limiter value, if the temperature does not drop by 2°C
( ) or more within the loop disconnection detection judgment time set, an alert is output. (The operation is
reversed for forward action. ( Page 252, Section 4.21))
Standard