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Shunt Resistor Current Sensing Method

Writer:Microhm Page View:Date:2019-08-01
Selecting the proper method for current sensing is not a difficult thing. There are few factors need to be considered for choosing the right method, like:
1. How much accuracy is needed?
2. DC or AC measurement or both?
3. How much power consumption is required?
4. What is the current range and bandwidth to be measured?
5. Costing.
Other than those, acceptable sensitivity and interference rejection are also need to be considered.

A low-value resistor in series is used to sense the current. When the current flow through a low-value resistor, it produces a voltage difference across the resistor. Engineers can find full size of shunt resistors from suppliers, like Microhm Electronics which is specilized in shunt resistors manufacture with more than 5 years.
Suppose 1A of current is flowing through a 1-ohm resistor. As per ohm's law Voltage is equivalent of current x resistance. Therefore, when 1A of current flow through a 1-ohm resistor, it will produce 1V across the resistor. The wattage of the resistor is a critical factor to be considered. However, there are very small value resistors also available in the market, where the resistance is in mili-ohms range. In such a case, the voltage difference across the resistor is also very small. A high gain amplifier is required to increase the amplitude of the voltage and finally, the current is measured using the reverse calculation basis.

An alternative approach for this type of current sensing technique is to use the PCB trace as shunt resistor. Since the copper trace of a PCB offer very small resistance, one can use the trace to measure the current. However, in such an alternative approach, several dependencies are also a huge concern to get an accurate result. The main game-changing factor is temperature drifting. Depending on the temperature, the trace resistance gets changed resulting in an error result. One needs to compensate for this error in the application.
 The application of Shunt resistor includes digital amp meter. This is an accurate and cheaper method other than the Hall Effect sensor. The shunt resistor can also provide a low resistance path and allows an electric current to pass one point to the other point in a circuit.
 As every factor can’t be satisfied, some trade-offs are made to compromise one feature with the other depending on the application requirement priority.


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