96
Detecting Current Errors Section 4-5
(3) The OC Alarm can be forced ON or OFF, regardless of the actual heater
current value, by setting the OC (Heater Overcurrent) Alarm parameter to
0.0 or 100.0. Use the 0.0 and 100.0 settings to check operation.
(4) This parameter can be set only when operation is stopped.
The hysteresis setting prevents chattering at the detection point.
When this parameter has been changed, the new setting becomes effec-
tive the next time a software reset is performed for the Unit or the next
time power is turned ON.
• Control will be continued even when there is an OC Alarm.
• The rated current value may sometimes differ slightly from the actual cur-
rent flowing to the heater. Check the current value in an actual operating
state in the Heater Current Value 1 or 2 Monitor parameter.
• If there is little difference between the current in normal and abnormal
states, detection may become unstable. To stabilize detection, set a cur-
rent value difference of at least 1.0 A for heaters of less than 10.0 A, and
at least 2.5 A for heaters of 10.0 A or more. If the heater current is too low,
loop the load line several times through a CT, as shown in the diagram
below. Looping it through twice will double the detection current.
■ Heater Overcurrent Latch and Latch Cancel
The heater overcurrent latch can be used to keep a heater OC Alarm ON
once it goes ON.
The latch can be released by executing an operation command (Reset Error
or Software Reset), cycling the power, or setting the Heater Overcurrent
Detection Value to 100.0 A. Refer to 6-4-11 Operation Commands for details
on the operation commands.
Note This parameter can be set only when operation is stopped.
Installing Current
Transformers (CT)
(OC Alarm)
For details, refer to Installing Current Transformers (CT) (HB Alarm) on
page 88.
Calculating the Heater
Overcurrent
Detection Value
For details, refer to Calculating the Heater Burnout Detection Current Value
on page 89.
CT
Load line
Variable type Parameter name Setting range Default
E4/A4 Heater Overcurrent 1 or 2 Latch
(I/O)
0: Disabled
1: Enabled
0
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