How Precision Shunts Work, and Differences Between Shunt Resistors and Standard Resistors

Time：2015-10-24 15:36Hits：2857

There is a difference between the technical limitations of high precision shunt resistors and standard resistors. High precision shunt resistors are highly accurate and can offset the smallest ohmic values. If a Kelvin connection is used to achieve such high accuracy, this connection avoids issues such as lead resistance and sensitivity. High-precision shunts are also available for bench testing of equipment, which can be used in conjunction with a voltmeter to assess the level of current flowing through a circuit. Using a sensitive voltmeter will mean good safety when measuring larger currents than a standard multimeter.

There are many reversible and irreversible factors that can affect the value of a shunt resistor when working with shunt applications. The associated mechanical, electrical and thermal loads imply long-term stability and irreversible resistance changes. The temperature coefficient of resistance (TCR) is expressed in ppm/oC and corresponds to the drift due to cooling or heating of the transistor due to fluctuations in ambient temperature. The level of power a resistor must dissipate is expressed in Resistive Power Coefficient (PCR) or ppm/W.

Precision shunts are often used to protect speed controllers from loads that can draw excess current or limit the speed of an attached motor. The speed of the controller can be increased by disconnecting the shunt from the sense line. Then the sense wire will have to be grounded. There won't be any voltage drop, so the speed controller will generate as much power as possible. However, it can be dangerous if the load placed on the control transistor is too large.

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