An electrical signal can be applied to a nerve and the resultant evoked electrical signals or responses from the nerve to which the initial signal was applied, or other nerves or muscles connected to it can also be measured. The nervous system can be examined in this way. Such instruments that measure electrical signals or clinical electrodiagnostic instruments are mostly of analog type which makes use of a cathode ray oscilloscope (CRO) for signal processing and display.

The analog devices are incapable of numerical calculations. Digital electrodiagnostic instruments have at least one signal pickup channel and an optional stimulatory channel. The channels are connected to a dedicated microprocessor or personal computer through a system for data collection and control. The signal pickup channel comprises of a pair of pickup electrodes connected to a biopotential amplifier, a frequency filter and an isolator. The stimulator channel comprises of a pair of stimulation electrodes connected to an electrical stimulator. Data is collected by a data acquisition system. It includes components such asa digital converter, memory and timer.

Prof. S. Devasahayam of Department of Bioscience and Bioengineering had devised an electrodiagnostic instrument for electromyography (EMG) and nerve conduction measurement. It has signal pickup channel and stimulator channels which are connected to an audio jack connectable to a multimedia card of a PC. The pickup channel has been designed to be placed removably on the part of the body when tests are made. It is connected to a biopotential amplifier, a frequency filter and isolator. Similarly stimulatory system has electrodes, an input jack and isolator. The input signal generated from pickup channels are inputted by an analog signal generator. The system has software to control the input audio signals base values and collection of signals and measurement of the data needed.