Patent GB-707226-A (GB)
Title: Improvements in or relating to apparatus sensitive to thermal sadiation
IPC: G01J5/00
Filed: 1950-03-31
Abstract: 707,226. Thermal radiation apparatus. BAILEY METERS & CONTROLS, Ltd. March 31, 1950 [April 2, 1949], No. 8179/50. Class 40 (3) Apparatus responsive to thermal radiation comprises a bolometer bridge and circuit means for comparing a potential determined by the unbalance of the bridge with a second or reference potential. Smoke density measurement.-In Fig. 1 thermal radiation from a lamp 5 is directed through a tube 3 upon a bolometer 6. The tube 3 within its slot 4 receives a sample of the smoke flowing in stack 2 so that the radiation is variably absorbed dependently on the smoke density. The wire filament 12 in the bolometer 6 thus changes in resistance with change in smoke density and with ambient temperature compensating filament 10 forms two arms of an AC energized bridge 13 whose other two arms comprise fixed resistors 14, 15 and parts of bridge balancing resistance 18<SP>1</SP>. The output voltage eo of the bridge 13 is associated with an opposition voltage ex in a resistance network B, P, Rx, SW. The bridge output circuit which receives the voltage eo comprises a portion of resistor SW and an amplifier and control 21 which supervises the rotation of a motor 23 ganged to the tapping 20 on resistance SW and to a pen 24 on a recorder 1. In use a change in smoke density sensed by the bolometer 6 changes eo and the controller 21 reacts to rotate motor 23 and move the tapping 20 on resistance SW to reinstate a predetermined or calibrated relationship or balance between ex and eo and simultaneously move the pen 24 on the recorder 1. In setting up the apparatus for operation Rx is established for the distance between the lamp 5 and the bolometer 6, i e. maximum radiation available with zero smoke density and with P under this condition set to produce zero on the recorder 1. The calibrated condition for 100 per cent smoke density is obtained by completely blocking the tube 3 and using tapping 18 to balance the bridge 13 and establish 100 per cent smoke density reading on the recorder 1. The Specification discusses with the aid of a graph, Fig. 2 (not shown) the factors involved in selecting a particular value of bridge input voltage Eb to minimize measuring errors due to variation in supply voltage Eo. A modification, Fig. 3 (not shown) introduces a variable resistance in series with the bolometer 6 to compensate for errors due to re-radiation from the bolometer 6 affecting the radiation from the lamp or spotlight 5. This compensating resistance is adjusted by the motor 23 simultaneously with movement of the tapping 20 on resistance SW. Measuring temperature.-Fig. 6, provides a record of the surface temperature of a paper machine roll 56 emitting infra-red radiation on to the bolometer 6<SP>1</SP> which in this case is appropriately equipped with a quartz window 57. The setting up and operation in Fig. 6 is fundamentally the same as in Fig. 1. With appropriate adjustment for the temperature range involved circuit, Fig. 6, may be used for measuring the temperature of a moving billet, Fig. 5, as is demonstrated in Fig. 7. As the cross-section of the billet 51 is reduced its length increases and it takes more time to pass the bolometer 6 so that the temperature indications such as A, C, E progressively persist for longer periods of time. In Fig. 7 A represents the initial approach of the highly heated billet, B the return pass, C the second approach, D the second return, E the third approach &c. Miscellaneous.-The Specification includes Fig. 4 (not shown), a flame failure alarm system and an arrangement, Fig. 5-complete drawing-(not shown) for recording the speed and frequency of passing of heated billets, both arrangements being in common with Specification 707,270, and claims the feature in these arrangements of comparing a bridge determined potential with a reference potential which feature is not claimed in Specification 707,270. The A.C. source Eo, Fig. 1, energizing the equipment supply transformer 17 is also used to energize the spotlight 5. The holometer 6 or 6<SP>1</SP> is as described in Specification 707,225 and is enclosed in a housing 9, Fig. 1, together with the ambient temperature compensating resistance 10 which is shielded from the radiation affecting the bolometer 6. The amplifier and motor control gear 21 may be as disclosed in Specification 660,105, [Group XXXV].