ABSTRACT
All measurements are subject to error. Indeed, the very act of introducing a transducer into a system distorts the system and forms a possible source of error. Errors fall into two main categories: systematic errors arising from the configuration of the system; and random errors due to noise and interference. Interference is a random effect resulting from the influence or external parameters on the system, the major sources of which are time varying electrostatic and magnetic fields. Electrostatic interference occurs as a result of the presence of stray or parasitic capacitance which provides a path for the interfering signal. Power supply transformers are a major source of interference, particularly in the form of the mains hum caused by capacitive currents in the secondary of a transformer producing a common mode voltage. Noise is considered to be a signal varying randomly in both frequency and amplitude. White noise is constant power spectral density over a wide range of frequencies.
