Patent GB-1233801-A (GB)
IPC: G08B17/06
Filed: 1968-06-21
Abstract: 1,233,801. Measuring temperature electrically. J. E. LINDBERG. June 21, 1968 [Aug. 18, 1967], No.29631/68. Heading G1N. [Also in Divisions G4 and H1] A temperature detection system comprises at least one temperature sensor 22 arranged to switch a first resistor 35 into a circuit when the temperature is above or below a predetermined value and a further resistor 33 connected to indicating means 10 so as to provide discrete indication of the following conditions: - (a) The sensor 22 being in an "on" or "off" condition (indicating whether temperature is above or below a predetermined value (b) When the circuit is open (c) The existence of an earth fault on sensor 22. The sensors 21, 22 preferably comprise tubes 23, 24 each containing a wire of zirconium or titanium hydride which evolves hydrogen at elevated temperatures, the pressure of which deflects a diaphragm 27 from contact with the end 28 of the tube 23. This action inserts a resistor 34, 35 in series with coil 15 of ratiometer 10 having a standard coil 14. A nickel resistor 33 is included to provide continuous temperature indication of the ratiometer 10. The scale ratiometer 10 (Fig. 2, not shown) has a portion calibrated in degrees and a number of discrete areas corresponding to excess temperature at either of sensors 21, 22 or in both these regions and further discrete areas at either end of the scale indicative of open- or short-circuit faults. Alternatively, the pointer of the ratiometer may be replaced by a mirror, reflecting light on to a scale having a plurality of photo-resistive areas arranged to sound alarms, or actuate a fire extinguisher or transmit a radio. signal from an aircraft to ground. Temperature measuring bridges. Fig. 4 shows a pair of bridges for use in a redundant fire detector in an aircraft. Contacts 80, 81, 100, 101 represent the contacts of sensors 21, 22 (Fig. 1) whilst resistors 66, 67 represent the nickel temperature-dependent resistor 33 of Fig. 1. The operation of resistors 66, 67 may be checked by closing contacts 62, 63 in circuit to heaters 64, 65. The bridge balance is detected by milliammeters 73, 90, having mirrors reflecting light from lamps 87, 88 on to a calibrated scale. Switches 85, 103 may be closed to simulate a short-circuit or switches 84, 102 may be opened to simulate an open-circuit. Switches 78, 95 may be operated to test meters 73, 90. Cathode-ray tube discrete value indicators. Figs. 11 to 14 (not shown) relate to cathode-ray tubes having screens comprising areas of different coloured phosphors or overlaid by coloured transparent sections so that when the Y-plates are connected to a D.C. amplifier (fed from a temperature measuring bridge) the beam may be deflected to one of the coloured areas indicative of temperature or fault conditions. Multiple level discrete value indicators. Fig. 15 shows a D.C. amplifier 550 fed from a temperature measuring bridge and having tappings on a potential divider 590.... 594 feeding respective transistors 630 ... 632 having indicator lamps 640 ... 642. Transistor 632 responsive to the lowest voltage significant of excess temperature is arranged to operate a relay 672 which initiates audible and visible alarms 670, 671. In Fig. 16 (not shown) the potential divider 590 ... 594 is replaced by a plurality of voltage sensors connected in parallel with the output of amplifier 550 and each operating an individual indicator lamp. In Fig. 18 (not shown) the transistors are omitted and each conductor 610... 614 is connected via resistor to one electrode of a "nixie" neon indicator tube. "Floating" temperature alarm systems. Fig. 7 (not shown) relates to a bridge detector responsive to a series arrangement of sensors 21, 22 (as in Fig. 1), the circuit being isolated from earth and supplied via a double-wound transformer and full wave rectifier. An earth-leakage neon indicator is included together with circuits for preventing false alarms due to short- or open circuit faults.