Recording Instrument, Graphic

a measuring instrument in which a record of readings is provided in the form of a graph. Recording instruments are used for registering one or more physical quantities, such as voltage, current, resistance, force, temperature, humidity, displacement, or consumption, as functions of time or (less frequently) other physical quantities.

The simplest recording instrument comprises a measuring instrument whose moving part is connected to a marking device, such as a pen, pencil, or capillary tube, that leaves a trace on a moving medium, usually a paper strip chart. There are recording instruments for discrete recording (points, strokes, or other signs) and for continuous recording in the form of a curve. In order to register simultaneously several quantities that vary with time, a recording instrument is equipped with the corresponding number of marking devices and a wide strip chart having scales of the measured quantities across the width and a time scale along the strip. In this case, the measuring results for the different quantities are recorded with different signs or marks of different colors. The movement of the strip chart may be a step function of time; in this case, the recording has scales both for the measured quantity and for time.

Figure 1. Recording instrument for continuous recording of three voltages or currents in a three-phase network (for example, during a breakdown): (T₁), (T₂), and (T₃) electromagnetic transducers (voltmeters or ammeters), (P₁), (P₂), and (P₃) marking pens, (M) recording medium (strip chart), (D) drive system for the recording medium

There are many different systems of recording instruments, and they vary in their recording means, mechanism, design, and number of parameters recorded (Figures 1 and 2). The most familiar are the recording voltmeters, wattmeters, and automatic potentiometers, light-beam oscillographs, thermographs, and barographs. With the development of digital methods of measurement and the use of computers to process the results thus obtained, preference is being given to digital recording instruments with measurement transducers that convert electrical and nonelectrical quantities into information that is presented in digital form. Both permanent (panel-type) and portable recording instruments are manufactured.

Recording instruments are used when it is necessary not only to know the individual values of a measured quantity, but also to follow the variation in the quantity with time or as a function of other physical quantities. With such a recording it is possible to make a judgment about the evolution of a phenomenon under

Figure 2. Schematic diagram of a single-channel light-beam oscillograph: (1) light source, (2) condenser, (3) slit diaphragm, (4) prism, (5) electromagnetic vibrator, (6) prism, (7) mirror drum, (8) observation screen (ground glass), (9) cylindrical lens, (10) slit diaphragm; (M) photosensitive paper (the recording medium)

study, the progress of a production process, the operation of multi-unit machines that are being monitored, or the actions of personnel tending such machines.