Patent GB-936613-A (GB)
Abstract: 936,613. Measuring temperature electrically. CONSOLIDATED CONTROLS CORPORATION. Dec. 2, 1959 [Dec. 8, 1958], No. 40973/59. Class 40 (1). [Also in Groups XXXV and XXXIX] # A resistance thermometer system comprises a source of electrical power, a first resistance element having a substantially zero temperature coefficient of resistivity, a second resistance element having a temperature coefficient of resistivity such that the resistivity of the second element changes substantially over a given temperature range, means connecting the first and second elements in predetermined circuit configuration so as to be energized from the source of electrical power, the voltage across the first resistance element, or the current through the second resistance element, being maintained substantially constant and an electrical output signal being produced which is proportional to the difference between first and second electrical signals derived from the first and the second resistance elements, respectively. The system shown comprises a measuring unit 10, a reference signal source 11, magnetic amplifiers 12 and 13 and an output signal magnetic amplifier 14. The unit 10 comprises a temperature measuring resistance element 20, e.g. of platinum, molybdenum, copper or tungsten, and a reference resistor 21 of material having a substantially zero temperature coefficient of resistivity, such as manganin or constantan, and having the same resistance as that of the element 20 at some pre-determined temperature, e.g. 50‹ F. A constant voltage is maintained across resistor 21 by a regulating system including magnetic amplifier 12 which compares the voltage produced by the reference source 11 with a control signal derived from the resistor 21 and produces a correcting signal when these differ. The reference source 11 when connected to a 50v. A.C. supply produces across a Zener diode 34 a highly regulated rectified voltage which is supplied to a reference winding 25 through a level-setting potentiometer 35 which may also be adjusted to compensate for changes in the Zener diode characteristics. Magnetic amplifier 12 is of the full-wave type and includes a pair of gate windings 40 connected in series with a bridge-type rectifier circuit 41 to a 12v. A.C. supply. A positive feedback winding 42 connected to the rectifier 41 and through a resistor 43 to a control winding 45 of magnetic amplifier 13 provides high open loop gain for the amplifier 12. In order to derive a control signal from the reference resistor 21, the voltage produced thereacross is fed to a control winding 54 on the amplifier 12 through a stabilizing network consisting of resistors 50, 51 and 53 and a condenser 52 designed to prevent self-oscillation within the system. The magnetic amplifier 13 is of the half-wave type and includes a bias winding 60 energized from the 50v. A.C. supply through a resistor 61 and rectifier 62 to control the flux operating level in the core of the amplifier in conjunction with the control winding 45. The 12v. and 50v. A.C. supplies are synchronous and preferably derived from different windings on the same power transformer. An output gate winding 65 supplies a rectifier 66 and filter network 67 to provide across a condenser 68 a substantially unidirectional voltage which is applied to terminals 15 and 17 to produce a current flow through the series combination of resistors 20 and 21, the voltages produced across these resistors being fed to input coils 70 and 71 of the magnetic amplifier 14 which produces an output Eout proportional to the difference in these voltages. It is shown that since a constant voltage is maintained across the reference resistor 21, Eout = alphaT E ref. where alpha is the temperature coefficient of resistivity of resistor 20 T is the temperature being measured and E ref. is the constant reference voltage developed across the reference winding 25. A linearity winding 58 and potentiometer 80 are provided to correct for non-linearity of a, and the signal supplied to the winding 58 may also be employed to compensate for changes in the resistance of the control winding 54 with temperature. The output signal may be accurately reproduced if a measuring unit 10 of the same material but having a different resistance value at the same reference temperature is used. The system also provides lead wire compensation since extraneous voltages picked up by the wires connected to the coils 70 and 71 cancel out. Other types of amplifier may be substituted for the magnetic amplifiers 12, 13 and 14, and if the difference in voltages# across the resistors 20 and 21 is large it may be measured by a meter arrangement in place of the magnetic amplifier 14. Modified arrangements are described (Figs. 2 to 4B, not shown) for measuring over two ranges simultaneously by adding a second reference resistor to the unit 10 and for measuring the average or difference of temperatures at two localities using . two units 10 with either one or two regulating systems. In an alternative arrangement (Fig. 5, not shown), the resistors 20 and 21 are connected in parallel and the regulating system maintains the current through the resistor 20 substantially constant.