Ambient
If the ambient temperature of the area in which the shunt is to operate exceeds the ambient Reference Test Conditions, a de-rating factor must be applied to prevent the manganin temperature from going above the safe limit of 125°C. The following formula may be used to find the de-rating power.
Pout = Pmax x (1-T/A)
Pmax = Prated x 0.66
where T is the difference between the rated and operating ambient temperatures, A is the rise allowed above the rated ambient and Pmax is the Pout at 25°C.
Example:
If a 150 Amp 50 mV shunt is to operate in a 100°C ambient, what is the maximum load?
100°C is 75 degrees above the ambient, so T = 75°C, and the rated rise A is 100°C.
Therefore:
Pout = Pmax x (1-75 / 100) = Pmax x 0.25
Pmax = 0.66 x Prated = 0.66 x (150 x 0.05) = 4.95 watts
Pout for an ambient of 100°C is Pout = 4.95 x 0.25 = 1.23 watts,
60 Amps will be the maximum load.
Canadian Shunt Industries Ltd
80 Bullock Drive, Unit 1
Markham, ON L3P 3P7
Canada
1.800.433.5604
T 905.294.5274
F 905.294.5096
