Patent GB-1451545-A (GB)
Title: Temperature measuring device for high ambient temperature conditions
IPC: G01K7/16
Filed: 1974-02-25
Abstract: 1451545 Measuring temperature electrically FELTEN & GUILLEAUME CARLSWERK AG 25 Feb 1974 [23 Feb 1973] 8439/74 Heading G1N [ Also in Division H3] Temperature-measuring apparatus for use in high ambient temperatures includes a temperature sensing member and an input section comprising an A/D converter connected to the sensing member, abinary store, ancillary circuitry and a power pack, the input section being housed in a thermally insulated container separate from other parts of the apparatus. A glass-clad Pt wire 5, Fig. 4, for sensing the temperature in a preserving can 1 during sterilization in an autoclave, is fused to a glass stem 6 inserted into the cover of the can 1 through an aperture provided with a seal 9. The stem 6 is fused to a metal sleeve 7 flexibly mounted on a thermally insulated vessel 2 by watertight bellows 8. The can 1, separated from the vessel 2 by spacers 3, is held in place by braces 4. Besides thermal insulation the vessel 2 may be provided with masses having high specific heat, or having high latent heat at a melting point below the rated maximum temperature of the apparatus. The apparatus housed in the vessel 2 includes an A/D converter Fig. 1 and a binary store Fig. 3 (not shown). The p.d. across the Pt wire 5, shown as RT in Fig. 1 fed from a constant-current source T 1 , is compared by the amplifier V with the p.d. across a reference resistor R v  carrying current I v  constituted by a constant reference I 2  and a combination of binary-weighted currents supplied by those of transistors T 3 -T 8  which are switched on by the output from a counter CO. Starting from a reset condition wherein T 3 -T 8  are all off, a minute clockpulse at a terminal MT will start the counter CO in response to counting pulses from a terminal ZT, if a gate G 1  is opened by an amplifier output AV indicating that the resistance RT exceeds a reference value so as to give rise to a differential voltage UD. As counting proceeds, counter outputs A-F selectively switch transistors T 3 -T 8  to increase the current I v  by a standard increment at each counting pulse, until counting is stopped by the nulling of UD. A resulting negative pulse at the amplifier output AV gates a store (MDS), Fig. 3 (not shown) to accept outputs A-F from the counter CO and, when further instructed, to transfer the information to other apparatus, e.g. a D/A converter, digital indicator or recorder, remote from the hot area. The store MDS has a capacity overload protection circuit which, if at least one of the store outputs (A<SP>1</SP>-F<SP>1</SP>) goes positive, switches off the clockpulses to the store to stop further measurements being accepted. A further protection circuit Ti i Fig. 1 senses if the temperature resistor RT is disconnected and permanently switches the counter CO to 'reset'. The apparatus may be modified to use a thermocouple instead of a resistance RT, by discarding the source of current IT. Self-heating of the apparatus in the vessel 2 may be reduced by arranging that certain parts of the apparatus, including the sensing resistor RT, are switched on only during clockpulses.