Coaxial cable
The technique is used in equipment such as sensitive photomultiplier tubes, electrostatic sensors, precision low-current measurement, and some medical electrography machines, where leakage current would alter the measurement. Any situation in which the source to be measured has a very high output impedance is vulnerable to leakage current and if sufficient insulation is not practical then a driven shield may be required. Coaxial cable is well suited for use as a guard; if electromagnetic shielding is also required then triaxial cable may be used as depending on the type of buffer circuit any noise on the guard may be amplified in the output.