Kelvin (4-terminal) connections are used for these low ohmic value products to measure a precise voltage drop across the resistive element. In these applications the contact resistance, lead resistance, and their TCR effect may be greater than that of the resistive element itself and could cause significant errors if the standard 2-terminal connection is used. Figure 4 shows a high impedance measurement system where r5 approaches infinity and Im approaches zero resulting in negligible IR drop through r3 and r4 which negates their lead resistance and TCR effect. With the voltage sense leads E1 and E2 inside of r1 and r2 the resistance and TCR effect of the current leads, I1 and I2 are negated and only the resistance and TCR of the element R are sensed. This method of measurement is essential for precise current sensing.
Current Sense resistors are supplied by Texas Components with 4 leads or terminal connections to facilitate a standard Kelvin Connection.