Reducing Electrical Noise in Instrument Circuits

Overview:

This paper presents the results of tests conducted on ways of reducing the four types of noise encountered in electronic instrument circuits.

The use of computers and other sensitive electronic equipment in process instrumentation systems has demanded that more attention be give to electrical noise pickup in instrument circuits.

The superior performance of aluminum-Mylar tape shields in comparison with copper braid and copper served wire shields for static noise rejection is described.

The effect of twisting wires to cancel magnetic noise is compared to various shielding materials. Twisting the wires is shown to be the most effective practical way of reducing magnetic noise.

The control of common mode noise by the proper grounding of shields in thermocouple circuits is shown. The use of single grounding points in shield circuits grounded at the couple is recommended. Multipair cables with individual isolated pair shields are recommended.

Comparative results on cross talk elimination in multipair cables are presented. Individually shielded pairs are recommended as the most practical means of cross talk rejection in instrument circuits.