How MicroOhmmeters Measure Very Low Resistance

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MicoOhmmeters or digital low resistance Ohmmeters are essential tools used for finding problems in metal connections. Ohmmeters cannot measure the low resistances of metals because they use a different measuring method. MicroOhmmeters use an enhanced method that allows them to measure low resistance values accurately. 

An Ohmmeter cannot measure low resistances because it often employs a Wheatstone in measuring resistances. The stray resistances caused by the connections and terminals affects the balance of the bridge resulting to inaccurate measurements. A 
DLRO uses a Double Kelvin Bridge also known as a Thomson Bridge to counteract the problem. The equation for the Double Kelvin bridge is Rx/Ra= RN/RM+Rwire/Ra(Rm/Rm+Rn=Rwire)(RM/RM-Rn/Rm). Where the equation is almost the same with the Wheatstone bridge except that the stray resistances are added to cancel their effects on the readings. As long as the ratios of RN RM and Rm Rn are the same, the bridge will be balanced even with the presence of stray resistances.

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