Patent GB-1453709-A (GB)
Title: Monitoring system
IPC: G01D7/08
Filed: 1973-12-05
Abstract: 1453709 Indicating apparatus: measuring IC engine variables TEXAS INSTRUMENTS Ltd 5 Dec 1973 56388/73 Headings G1J and GIN [Also in Division G4] A monitoring system having a single display H on which can be displayed successively and/or selectively the values of a number of variables being monitored, comprises a multi-plexing switch A, controlled by a sequence timer C, for applying electrical signals representing the variables successively to a common conductor feeding a single analogue to digital converter F which produces a succession of digital signals representing the variables, and display control means G, H for receiving each digital signal to produce a corresponding indication on the display H, the common conductor including a circuit B for making the ranges of the signals representing the variables similar for all the variables. In a system for a motor vehicle, the  electrical resistance of transducers T1, T2, T3 supplied with constant currents from sources 51, 52, 53 is a logarithmic function of fuel level, engine oil pressure, and coolant temperature respectively. Their output voltages are applied in turn by the multi-plexing switch A to the input of a logarithmic amplifier B (see Division G4) giving output voltages approximately linearly related to fuel level, oil pressure, and coolant temperature. Switching of reference voltages by the sequence timer C brings the output voltages of the amplifier B within the same range of magnitude for each variable. The amplifier B outputs pass via a linear amplifier D to a switch E controlled by the sequence timer C to add the scaled battery voltage to the sequence of signals before they reach the analogue to digital converter F. The digital signals produced pass to a diode matrix (G) Fig. 6 (not shown) controlling the display H and an alarm panel X which includes a warning light to show when each monitored variable goes outside a predetermined safe range. An additional light L in the panel X is illuminated if a braking light is not working. A push-button array M acting on a relay K of the display control enables the desired variable to be selected for display, the signals from the other variables being blocked from display. The display may comprise electroluminescent seven segment decimal digit units 2, 3, Fig. 2, and a two segment unit 1 for the most significant digit, which need show only a 1 or a blank. A decimal point member 4 is provided. Fig. 3 shows a linear analogue display, the required number of segments being illuminated under control of the diode matrix G to represent the magnitude of the variable selected. Electroluminescent segments 10, 11 provide upper and lower alarm indications. Fig. 4 shows a second analogue display in which radial lines of electroluminescent segments are selectively illuminated to mimic a pointer moving round a dial. The alarm circuits may be triggered only after a predetermined number of out-of-range signals occur in a sequence of cycles of the multi-plexing. In the case of engine oil pressure, different critical values may be used, one when the engine is idling, and a higher one for normal working speeds.