The initial resistance deviation of the resistor
The initial resistance deviation of the resistor,This is familiar to everyone. Like commonly used thick film resistors (such as 0603 packages), the general accuracy is 1% or 5%. It refers to the resistance deviation at room temperature. The initial resistance deviation is fixed after leaving the factory, such as the nominal resistance value. The resistance is 100Ω, the actual measurement is 101Ω at room temperature, and the initial deviation is 1%.
Insert a sentence here, regarding the resistance accuracy, the specification generally gives an accuracy, in fact, this is the initial deviation, or the accuracy in a narrow sense; and the actual resistance value will be affected by many factors.
For the shunt, of course, the smaller the initial deviation, the better, but the initial deviation can be compensated by calibration, so the initial accuracy of the shunt does not need to be particularly high.
Temperature Coefficient of Resistance TCR:
The temperature coefficient of resistance (temperature coefficient of resistance), which means the relative change of the resistance value of the resistance when the temperature changes by 1℃, the unit is ppm/℃ or ppm/K; the resistance value of the resistance is not a constant, it changes with the temperature change, That is, temperature drift, and TCR is a quantity used to describe the degree of temperature drift.
However, since TCR is nonlinear, in order to clarify the magnitude of the temperature drift, the average TCR is usually used, and its calculation formula is as follows (the picture comes from KOA); .
When we use the shunt, the real TCR is at the sampling point; so usually in order to correct the influence of the TCR, we also use the calibration method to obtain and compensate the TCR curve in advance to the actual calculation.
Shunt heating problem:
In order to reduce the negative effects such as temperature drift, the direct measures are to increase heat dissipation and select a shunt with high power; in addition, some factors cannot be ignored.
For example, the contact resistance between the shunt and the copper bar will also affect the accumulation of heat (the picture is from the official website of Ruisi); this contact resistance is related to the installation torque, generally within a certain range, the greater the torque, the smaller the contact resistance; In addition, it is related to the coating on the surface of the shunt. Compared with nickel plating and OSP, the contact resistance of tin plating will be smaller.
