Control the surface temperature of the shunt is far more important than you think
Is to show the basic unit of the current in the international system of units.
International metrology committee is defined as: a vacuum 1 meter apart two infinite parallel straight wire and circular cross section can be ignored by a constant current, when the force between the two wires per meter length equal to 2 & times;
10-7 Newton, the regulations, the current in the conductor to one ampere.
But in the definition of two infinite long wire could not be achieved, in practice, by measuring the voltage drop of shunt combined with ohm's law to calculate the current.
As shown in the figure below, the dc shunt by the middle of the two copper joints and resistance alloy joint made of four terminal wiring method is used to shunt can precisely measure the current size.
Shunt need to work in a large power flow, because the heat would result in higher surface temperature of the shunt.
Especially in the environment under the condition of higher temperature and the thermal environment is poor, the surface temperature of the shunt rise further.
According to the IEEE standard, under normal working conditions of shunt suggest working current should not be more than two-thirds of the rated current.
But in the practical application often need to measure a wide range of current, namely we require shunt can be 10%
100% of the rated power back to normal work, sometimes even have a short-time overload.
Whatever the working conditions, the control of the shunt surface temperature is very important, in the 30 -
Its work best when the 70 ℃, and in any case the surface temperature cannot exceed 145 ℃, otherwise it will lead to irreversible changes in the value of resistance alloy.
In particular, should be the center of the resistance alloy measuring the surface temperature of the shunt.
Need to measure a wide range of current can cause heating situations of dc shunt difference is huge.
Resistance of the resistance caused by loading of the thermal resistance changes, different current load, the resistance changes of resistance is also different.
This due to the thermal resistance changes we use power coefficient (
To describe, the unit for A PPM/A, use the following formula: the smaller the power coefficient, due to the thermal resistance changes is smaller, in the case of low and high electric current work flow the precision of the difference is smaller.
Data is shown in the list below, we have a claim of 0.
Level 5, 100 a, 75 mv shunt, in its precision greater than 0 10% rated current at room temperature environment.
6%, the serious super poor.
Power factor (
The size and the temperature coefficient of resistance alloy (
Size is related to production of low power factor of the shunt must use low temperature wave resistance alloy, we split step a electronic shunt the same measurement, the measurement result as the zhejiang the shunt rated current of the rectifier production from 10 a minus
50 ka, the highest precision of 0.
Level 5, has the very good long-term stability.
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If interested in our dc shunt or there is doubt, welcome your consultation.