Most recorders use a pointer attached to the stylus, so that the instantaneous value of the quantity being recorded can be measured directly on a calibrated scale. The markings on the paper are done with chopper bar, which applies the pressure chart the paper. This paper consists of a paper base coated with a layer of coloured dye black, blue or redwhich in turn is coated with a thin surface of aluminium. The basic element of a Strip Chart Recorder Working Principle consists of a pen stylus used for making marks on a movable paper, a pen stylus driving system, a vertically moving long roll of chart paper and chart paper recorders mechanism and a chart speed selector switch, as shown in Fig. Most recorders use a used strip attached to the stylus.
Markings on the paper are achieved by applying a potential of 35 V to the stylus. The advantage of impact printing over the pen and ink method is that, it can record data on up to 20 variables simultaneously. This system requires a thermally sensitive paper which used strip chart recorders its colour on application of heat. In some mechanisms, pressure sensitive paper is used.
This is achieved with the help of a wheel with an associated ink pad which provides the ink for the symbol on the wheel. The wheel is moved across the paper in response to the variable being recorded. The frequency of the chopper bar is once per second. The stylus pen consists of a tungsten wire moving over the aluminium surface. This system used strip chart recorders a thermally sensitive paper which changes its colour on application of heat.