Patent GB-931045-A (GB)
Title: Signal difference detecting apparatus
IPC: G08C15/08
Filed: 1961-10-18
Abstract: 931,045. Electric analogue computers; electric tests. HOWELL INSTRUMENTS Inc. Oct. 18, 1961 [Nov. 9, 1960], No. 37440/61. Class 37. [Also in Groups XXXVIII and XL (c)] In a system comprising a plurality of input means each carrying a variable signal, means are provided to detect the relatively highest value and the relatively lowest value signals. The system is described with reference to apparatus for determining the temperature range among a plurality of thermocouples, e.g. in the tail cone of a gas turbine engine. The thermocouples are sequentially monitored by apparatus adapted to seek and hold the thermocouples with, in alternate monitoring cycles, the highest output and the lowest output, respectively, these outputs being passed in opposition through a meter which indicates the temperature range existing among the thermocouples; alarm means may be operated when this range exceeds a predetermined value. Indication may also be given to identify the thermocouples with the highest and lowest outputs. As shown, the ungrounded leads of thermocouples T/C1 ... T/C8 are connected in turn to a conductor 10 through the upper contacts of relays K-1 ... K-8. Monitoring is initiated by the application of a positive potential B+ to a relay K-17 which operates momentarily to apply B + to the base of a transistor Q-1, thus rendering Q-1 conductive. Relay K-9 in the collector circuit of Q-1 comes up; connecting B+ to a capacitor C-2 and to K-1, which operates. K-17 falls back, followed by K-9; C-2 discharges to render transistor Q-2 conductive so that, as K-1 is de-energized, K-2 is energized by the operation of K-10. This sequence is repeated along the stepping chain K-9 ... K-16 until the latter falls back, when the discharge of capacitor C-3 renders Q-1 conductive, thus initiating the next cycle. The ungrounded leads of T/C1 ... T/C8 are also permanently connected via conductors 14 to the upper gang contacts S-1A of a high memory stepping switch S-1, and to the upper gang contacts S-2A of a low memory stepping switch S-2. Both stepping switches also comprise lower gang contacts S-1B, S-2B, respectively, which are normally connected to B+ through conductors 12; however, energization of K-1 ... K-8 operates to disconnect an associated contact in each lower gang from B+. The wipers of S-1A, S-2A are connected to contacts of a relay K-18, while the wipers of S-1B and S-2B are connected, through their respective stepping windings, to alternative contacts of a relay K-19 which according to its condition connects one or other, via the contact of a relay K-20, to earth when K-20 operates. Assuming that the bi-stable circuit comprising transistors Q-9, Q-10 is in the condition that Q-9 is non-conductive and Q-10 is conductive, the condition of de-energized relay K-18 is as shown, while relay K-19 is operated to connect the wiper of S-1B to the contact of K-20, and the apparatus seeks the highest output thermocouple. As the monitoring cycle proceeds, the output of each thermocouple in turn is applied via conductor 10, and conductor 34 to a contact 34a, while the output from the thermocouple connected to the contact of gang S-1A on which the wiper is resting is applied via a conductor 36 to a contact 36a. The potentials on 34a and 36a are compared by a chopper switch K-21, energized by A.C. from a first secondary winding 40 of a transformer T-1, any differential appearing being amplified in a phase-sense conscious circuit comprising transistors Q-11 Q-18. If the polarity of the differential indicates that the output at 34a of the currently monitored thermocouple exceeds that of the pro tern reference thermocouple at 36a, Q-18 produces an output which brings up K-20 to ground the wiper of S-1B which is thereby rotated until it reaches the contact from which B+ has temporarily been removed. This contact is associated with the thermocouple of higher output, and this higher output is fed, via the wiper of S-1A to become the new reference at 36a. Thus, at the end of the cycle the wiper of S-1A is passing the output of the highest-output thermocouple to one side of a meter M. The discharging of capacitor C-3, in addition to initiating the next monitoring cycle, also alters the condition of the bi-stable circuit (Q-9, Q-10) so that during the said next cycle, K-18 is energized, K-19 is in the de-energized condition shown, and the apparatus seeks the lowestoutput thermocouple. Now the pro tem reference is applied via the contact of gang S-2A on which the wiper rests and conductor 34 to 34a, while the monitored outputs on line 10 appear at 36a. A differential indicating that the output at 36a is below that at 34a causes an output from Q-18 and the subsequent grounding, by operation of K-20, of the wiper of S-2B which rotates until it reaches the contact associated with the currently monitored thermocouple. Thus, at the end of this cycle the wiper of S-2A is passing the output of the lowest-output thermocouple to the other side of the meter M, which consequently indicates the difference in outputs between the highest- and lowest-output thermocouples. If this difference exceeds a desired value, alarm means 52 operates. Indicators associated with S-1 and S-2 may identify the highest- and lowestoutput thermocouples, respectively. Amplifier, Fig. 1D.-This comprises transistors Q-1 ... Q-15 connected in cascade, the output of Q-15 being passed via a transformer T-2 to transistors Q-16, Q-17 arranged in pushpull to drive the final stage Q-18. Since an output from Q-18 is desired only when contact 34a is at a higher potential than contact 33a, a second secondary winding 42 of transformer T-1 is connected via rectifiers CR-6, CR-7 to stages Q-16, Q-17, respectively. T-1, T-2, and relay K-21 are so poled that when the input to Q-11 is of the desired polarity, it appears in the secondary of T-2 in phase with the signal in the secondary 42 of T-1; thus Q-16 and Q-17 are turned on during their correct half-cycles, and Q-18 produces an output. If the input to Q-11 is of the wrong polarity, however, it is out of phase with the signal in 42, and no output appears from the amplifier. The amplifier circuit is arranged in known manner to respond only to signals above a selected value, and to produce no output when the input is zero.