Effect of supply system on the reading of electronic measurement devices

Conclusions

• 1. An equivalent circuit is obtained which makes it possible to perform calculations associated with determining the effect of the supply system on the readings of an EMD with an asymmetric input circuit. A technique for determining the parameters of the equivalent circuit has been developed. A comparison of the theoretical and experimental data show them to be in satisfactory agreement. The values of the parameters are suitable for calculation when operating with a device supplied by the same supply voltage for which they are determined.

• 2. The noise current distorting the results depends upon the position of the two-pin plug supplying the device (particularly when supplied by a phase voltage). This is due to asymmetry in the power transformer. Of the two possible positions of the two-pin supply plug we should select the one for which the noise is a minimum.

• 3. By electrically connecting the common point of the measurement object, device housing, and supply system “ground” (if this does not distort the mode of the circuit used as the measurement object), we can eliminate the effect of a number of considered parasitic couplings. However, we should remember that the grounded common conductor must have a very low impedance. It is not possible to connect to this conductor sources having a high-level signal since as a result of the voltage drop on the common part of the grounded conductor additional parasitic coupling can appear.