Patent GB-1344630-A (GB)
Title: Electronic apparatus for anticipating the final value of a condition being monitored
IPC: H03M1/00
Filed: 1971-04-23
Abstract: 1344630 Measuring resistance: measuring temperature IVAC CORP 23 April 1971 [15 June 1970] 50370/70 Heading G1U In order to obtain rapidly an estimate of the temperature which a thermistor R T , Fig.2, forming one arm of an automatically balanced bridge, is approaching, this being shown by the solid-line graph, Fig. 4, in a first embodiment Fig.1, (not shown) and Fig. 5 the balance of the bridge is deliberately offset by an amount corresponding to 1‹F, and the bridge is allowed to follow the rising temperature (so that the indication provided by the bridge of temperature is 1‹F, higher than the actual temperature) until the rate of rise of temperature falls below a pre-set threshold level whereupon the indication provided by the bridge is held constant - it being assumed that the limiting temperature will be 1‹F higher than the actual temperature at which the rate of change falls below the pre-set threshold - and in a second embodiment Fig. 7, (not shown the bridge is allowed to follow the actual temperature for a pre-set time, e.g. 15 secs, and then a deliberate offset proportional to the rate of change of the temperature at the end of the fixed period is introduced into the brige which offset is rapidly followed by the bridge balancing loop so that an output indication higher, by an amount proportional to the rate of change, is produced. The system is particularly adapted for measuring human body temperature, and is said to produce accurate results in about 15 seconds as opposed to 2-4 minutes. In the first embodiment the unbalance signal 11, 12, Fig.5, from the bridge is amplified 13 to control the application, via a gate G1, and a monostable FF3, of clock pulses 40 to a counter 15 which switches further resistors, R 1 , R 2 , &c., Fig. 2, in parallel into the bridge to maintain balance. Each pulse from the monostable FF3 also discharges a capacitor 45 which charges towards the positive supply 50 between pulses. When the pulses from the monostable FF3 are sufficiently widely spaced in time, which occurs when the rate of change of the temperature of the thermistor is sufficiently low, capacitor 45 charges to such a level that a trigger FF2 is set. This closes the gate G1, thereby preventing any more pulses being applied to the counter, and energizes a "read light" 46. In the second embodiment Fig. 7 (not shown) each clock pulses fully charges a capacitor and the potential to which it falls between pulses is used as a measure of the rate of change of temperature. After a fixed time set by a monostable this potential is amplified and switched into the bridge which immediately rapidly rebalances itself to produce the desired indication. With suitable modifications non- electric variables other than temperature may be estimated. The system described with reference to Fig. 5 (and in the reference to Fig.1, not shown) also includes the feature that if the initial temperature of the thermistor when a measurement cycle is started exceeds 89‹F, i.e. if the initial temperature is close to the likely final temperature, then the anticipatory feature - which constitutes the invention - is inhibited and the system functions as a conventional measuring system continuously indicating the actual temperature of the thermistor. This is effected by a mode control flip-flop FF1. Initially the system is reset by generator 31 so that the counter 15 registers 90 and the mode control flip-flop has its upper stage ON indicating that the anticipatory mode is to be performed. The thermistor temperature is then compared, by the bridge, with 89‹F, since a switch 36 is turned on, and if the thermistor temperature is above 89‹F a signal is produced by amplifier 13, which signal, in addition to causing a clock pulse to pass through gate G1 to advance the counter, as described above, also passes via a gate G2 to set the mode control flip-flop FF1 to its non-anticipatory state, gate G2 being held open sufficiently long to allow the signal from amplifier 13 through by the reset generator 31. If the thermistor temperature is initially below 89‹F, then by the time that it has risen to above 89‹F so as to cause an output signal from amplifier 13, gate G2 will have been closed. When the mode control flip-flop FF1 is in its non-anticipatory mode state, i.e. with its lower stage ON, a diode 52 is conductive and capacitor 45 cannot charge, so that irrespective of how widely spaced the pulses from flip-flop FF3 become, flip-flop FF2 is never set.