Shunt resistive circuits are used for bypassing a specific amount of current around precision electronic instrument. The most common of these circuits used for bypassing, or shunting, is in an electronic circuit that uses a precision meter device. If a shunt resistor was not used, the meter could become damaged by an excessive current flow though the delicate movement. By following a procedure using Ohms Law, the proper shunt can be calculated for a protected meter circuit. The base of Ohms law is V=IR, where V is equal to voltage, I is equated to current and R is the resistance.
Instructions
1. Use the derivative of Ohms Law to find the proper shunt resistance where (Rs = Vm/Is). (Rs) is equal to the resistance of the shunt. (Vm) is equal to the voltage across the shunt and meter movement which results from the formula (Vm = Im X Rm). (Im) is equal to the current through the meter and (Rm) is equal to the resistance of the meter. (Is) is the current though the shunt.
2. Find (Is) first if you have a known current through a basic electronic circuit that consists of a resistive shunt, a meter and a power source that delivers 50 ma where (ma) equals mille amps. The meter deflects and reads 10 ma. The result would be (Is = It-Im) where (It) equals current total and (Im) equals the meter reading. The current through the shunt would then be 50 ma (It) minus 10ma (Im) which is equal to 40 ma.
3. Find the voltage of the circuit if the meter has an internal resistance of 8 ohms. Using the base of Ohms Law, Vm=Im X Rm, then the voltage across the meter would be 10 ma or 0.01 a (Im) times 8 ohms. (Rm) would equal 0.08 volts (Vm).
4. Take the current found in step 2 that runs through the shunt resistor of 40 ma or 0.04a combined with the circuits voltage of .08 volts to find the correct resistance of the shunt resistor.
5. Use the formula given in Step 1, the derivative of Ohms Law, and plug in the numbers to solve the equation of Rs = Vm / Is . Rs would then equal 0.08 (Vm) / 0.04 (Is) = 2 ohms.
Tags: current through, shunt resistor, base Ohms, circuit that, circuits used, circuits used bypassing, derivative Ohms