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"The Poor Man’s Milli-Ohm Meter" is a simple, cost-effective device designed to measure very low electrical resistances, typically in the milliohm range. It is often built using readily available components and can be a valuable tool for hobbyists, students, and engineers who need to measure small resistances without investing in expensive equipment.
The device generally operates by passing a known current through the resistor under test and measuring the voltage drop across it. Using Ohm's Law (V = IR), the resistance can then be calculated. This method is effective for measuring low resistances because it minimizes the influence of contact resistance and lead resistance.
To build a basic version of this meter, you typically need a stable current source, precision resistors, a voltmeter (or a multimeter with millivolt sensitivity), and some connecting wires. Additional components may include operational amplifiers, a microcontroller for more advanced designs, and a display to show the measured resistance directly.
While this device can be very useful, it has some limitations. Its accuracy is dependent on the precision of the current source and the voltmeter. It may also be affected by thermal EMFs, contact resistance, and lead resistance if not properly managed. Additionally, the range of resistance it can measure may be limited compared to commercial milliohm meters.
To improve accuracy, use precision components, such as low-tolerance resistors and a high-accuracy voltmeter. Ensure good connections to minimize contact resistance, and use a four-wire (Kelvin) measurement method to eliminate the influence of lead resistance. Additionally, calibrating the device against known standards can help ensure more reliable measurements.