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Detecting Heater Burnout (4-channel Models Only)
Calculating the Detection Current for Heater Burnout
Application Example
SSR
Heater
1 kW
CT
19
21
SSR
Heater
1 kW × 3
CT
19 21
Example:
• Heater burnout detection status can be confirmed by reading the status
for individual channels.
Use the following formula to calculate the detection current.
Normal current + Burnout current
Set value =
When two or more heaters are connected through the current transformer, set
the detection current to detect burnouts on the heater with the smallest cur-
rent. If the heater currents are all the same, set the detection current for one
wire.
Example 1: Using one 1-kW heater (200 VAC)
Normal current =
Burnout current = 0 A
200 VAC
Set value =
(Normal current − Burnout current = 5 − 0 = 5 A ( ≥ 2 A))
The above calculation produces 2.5 A. The minimum setting unit is
1 A, so 2.5 is truncated and 2 A is used.
Example 2: Using three 1-kW heaters (200 VAC)
Normal current =
Current for 1 heater =
Set value =
200 VAC
(Normal current − Burnout current = 15 − 1 0 = 5 A ≥ 3 A)
The calculation produces 12.5 A. This is truncated to 12 A, as
explained above.
2
1000
= 5 A (< 10 A)
200
5+0
= 2.5 A ≅ 2 A
2
1000
× 3 = 15 A ( ≥ 10 A)
200
1000
× 2 = 10 A
200
15+10
= 12.5 A ≅ 12 A
2
Section 4-4
27
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