94
Detecting Current Errors Section 4-5
Note (1) In the above diagram, power is considered to be OFF (normal) if the leak-
age current is less than the HS alarm current during the OFF time. If the
SSR output is short-circuited, the measured current will increase beyond
the HS alarm value and an HS Alarm will be output.
(2) HS alarms are not detected if the control output (heating) OFF time is
100 ms or less. Detection is also sometimes not possible if a contactor is
used for the control output.
(3) The HS Alarm can be forced ON or OFF, regardless of the actual leakage
current value, by setting the HS 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 HS 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 Leakage Current Value 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.
Control output (heating)
ON
OFF
ON time
OFF time
(See note 2.)
Variable type Parameter name Setting/monitoring
range
Default
D6/96
(See note 3.)
HS Alarm 1 or 2 (I/O) 0.0: HS Alarm ON
0.1 to 99.9 A
100.0: HS Alarm OFF
100.0
E4/A4
(See note 4.)
HS Alarm 1 or 2 Hysteresis
(I/O)
0.1 to 100.0 A 0.1
C5/85 Leakage Current Value 1 or
2 Monitor (I/O)
0.0 to 110.0 A ---
Conditions for use There must be a CT input.
CT
Load line
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