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Using Heater Burnout Alarm (HBA) Section 3-9
3-9-3 Calculating the Detection Current Value
• Calculate the set value by the following equation:
• To set the value of the heater burnout when two or more heaters are con-
nected through the CT, use the current value of the smallest heater con-
nected. If all the heaters have the same current value, use the current
value when one of the heaters burns out.
• Make sure that the following conditions are satisfied:
Heater of current 10.0 A or less:
Normal current −
Current at heater burnout ≥ 1 A
(When the resultant current is less than 1 A, detection is unstable.)
Heater of current 10.0 A or more:
Normal current −
Current at heater burnout ≥ 2.5 A
(When the resultant current is less than 2.5 A, detection is unstable.)
• The setting range is 0.1 to 49.9 A. Heater burnout is not detected if the set
value is 0.0 or 50.0. If the set value is 0.0, the heater burnout alarm is
turned OFF, and if the set value is 50.0, the heater burnout alarm is turned
ON.
• Set the total current value at normal heater operation to 50 A or less.
Application Examples Example 1 Using a 200 VAC, 1 kW Heater for OUT1
Example 2 Using Three 200 VAC, 1 kW Heaters for OUT2
Set value =
(Normal current + Current at heater burnout)
2
Heater
1 kW
CT
200 VAC
Control output
Current during normal operation =
200
1000
= 5 A (< 10 A)
Current at heater burnout = 0 A
Set value =
2
5 + 0
= 2.5 A
(Normal current
− Current at heater burnout) = 5 − 0 = 5 A (≥ 1 A)
Heater
1 kW
× 3
CT
200 VAC
Control output
Current during normal operation =
200
1000
× 3 = 15 A (≥ 10 A)
Current at burnout of one heater =
Set value =
2
15 + 10
= 12.5 A
(Normal current − Current at heater burnout) = 15 − 10 = 5 A (≥ 2.5 A)
200
1000
× 2 = 10 A
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