The technical constraints of shunts differ from standard resistors, precision shunts are high-precision resistors, low ohmic values. They can be expressed in micro-ohms when hundreds of amps must be measured.
Since accuracy is critical, current sensing is best accomplished with a Kelvin connection or a four-terminal connection that eliminates lead resistance and the undesired effects of lead on temperature.
Several factors can change the value of a DC shunt, and precision shunts are divided into reversible and non-reversible. Long-term stability is due to irreversible resistance changes due to mechanical, electrical and thermal loads.
The reversible effect is mainly composed of two parts: the temperature coefficient of resistance TCR: its unit is ppm/oC, which represents the drift characteristics of the resistance when it is cooled or heated under changes in ambient temperature. Resistor Power Coefficient PCR: Expressed in ppm/W, it characterizes the power that a resistor must dissipate.
An important parameter of a precision DC current shunt is the thermal EMF, which is not important for standard resistors. The variation of junction voltage with temperature in two different conducting materials explains why it is called thermal EMF or thermocouple effect and expressed in μV/oC. The rate of change of intermetallic voltage with temperature is a function of metal bonding.
On either side of the combination that is considered to be an input, the resulting voltage is either positive or negative in meaning. Assuming all resistors end up soldered to copper, then copper is the reference metal.
DC shunts are based on thermo-EMF, TCR and cost trade-offs, manganese alloy material is the most preferred shunt with exposed vanes. The shunt with exposed parallel wires is made of a metal alloy material, which is a manganese-copper alloy with a low temperature coefficient. Shunts encapsulated in heat sinks are usually manufactured by Resistor companies, E precision shunts have a near-zero temperature coefficient and are very sensitive to strain, and we often use our own precision DC current shunts.
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