Null balance recorder

A recorder is an electronic recording device which is used to record variables such as force, voltage, current, temperature, humidity, flow etc. Possible components of a recorder are graphic recording devices, computer printers, tape recorders, and cathode ray tubes. The two types of recorders are analog recorders and digital recorders. Analog recorders can be further subdivided into three. They are graphic recorders, oscillographic recorders and magnetic tape recorders. In a null balance recorder, a servomotor provides self-balancing action. Here a position type servomechanism which is applied to a variety of potential and bridge type circuits calibrated for different measurements is used. Signal which is to be measured is treated as input signal. Input signal is then compared with a reference voltage. A feedback system provides the reference voltage which is well calibrated with respect to a mechanical position on an output display scale. A servo amplifier compares the input signal and the reference voltage and then actuates a motor which positions an indicator on the output display scale for a zero error (null voltage condition) between the input signal and reference voltage. Based on the error signal producing source, there are three types of null balance recorders. They are potentiometer type, bridge type and linear variable differential transformer (LVDT) type.