Low Resistance Measurement Circuit

The low resistance measurement will indicate to the observant operator when.

Low resistance measurement circuit.

Low ohm meter measures 0 001 up to 1 999 ohm a very simple circuit to measure low resistance values from 0 001 up to 1 999 ohm. Thus to eliminate this issue small valued resistance are constructed with four terminals. 0 0 1 an ohmmeter measures the total resistance in the circuit including the resistance introduced by the test leads attached to the meter in addition to the resistance of any other wires in the circuit. 5 vdc and gnd hooked up to the top and bottom of the breadboard.

The major problem in measurement of low resistance values is the contact resistance or lead resistance of the measuring instruments though being small in value is comparable to the resistance being measured and hence causes serious error. C1 optional 0 1 microfarad ceramic capacitor to smooth the power supply. Top hooked to 5 v and bottom hooked to r2. There are special low resistance meters so called milliohm meter there are some which offer a resolution of 0 01µ ω which would be way overkill here.

In addition to having insufficient voltage or current sensitivity most dmms are no more sensitive than 1µv or 1na per digit dmms have high low level dc measuring instruments 1 3. In the above picture r is the unknown resistor and v is a multimeter set to read millivolts. What does the low resistance measurement tell the operator. Resistance r is the property of a circuit or element that determines for a given current the rate at which electrical energy is converted to heat in accordance with the formula w i2r.

Even with a much lower 1mω source resistance a 1µv measurement is near theoretical limits so it would be very difficult to make using an ordinary dmm. The practical unit is the ohm. The kelvin measurement can be a practical tool for finding poor connections or unexpected resistance in an electrical circuit. Low resistance measurement method basically the trick is to pass a stable known amount of current through the low value resistor and measure the voltage drop across it.

They internally work on the same principle. Obviously the multimeter is connected permanently as shown in picture. They use different constant currents based on the resistance range. Connect a dc power supply to the circuit and adjust the power supply so that it supplies a constant current to the circuit as shown in the diagram above within the circuit s capabilities of course.

C2 optional 10 microfarad tantalum capacitor to smooth the power supply. You must use two separate batteries.