Patent GB-817259-A (GB)
Title: Improvements in temperature alarm systems
Inventor: EVERETT ERNEST WALTER JAMES
IPC: G01K1/02
Filed: 1957-03-07
Abstract: 817,259. Temperature alarm systems. SPEED DEVELOPMENT CO. Ltd. Aug. 20, 1957 [March 7. 1957], No. 7600/57. Class 118 (1). Means for giving a signal to indicate a sudden change in temperature comprises a sensitive two-coil relay MR1. MR2 having a moving contact 10 engageable with a fixed contact 12 depending on the direction of the current flowing through its coils, the first such coil MR 1 being connected to a control source CS; a normally inoperative warning circuit adapted. to be made operative on engagement of moving contact 10 with fixed contact 12 and held independently of the said relay, such engagement of the moving contact 10 with the fixed contact 12 being arranged to cause energization of the second coil MR2 of the relay to urge the moving contact towards the fixed contact; and a further circuit set up on energization of the warning circuit and completed through moving contact 10 and fixed contact 12 for urging the movable contact to the "off " positions. The relay coils MR1 and MR2 form a galvanometer type of relay being pivotally mounted between 'the poles of a strong permanent magnet and the contacts 10 and 12 are normally separated by a light spring 13. To avoid the effects of vibration and the influence of high y-loadings likely.to be encountered in aircraft, this relay may be mounted on rubber buffers and dynamically balanced about its bearings. Operation.-In the event of a sudden temperature change a small current from the thermocouple control source CS flows through coil MR1 and contacts 10 and 12 engage. This sets up a circuit from the positive line 14. through normally closed reset button RB, resistance R2, coil M, contacts 12 and 10, coil MR2, normally closed button T, and through resistance R4 to negative line 16. The current flowing through MR2 adds to the effect of that flowing through MR1 and urges contacts 10 and 12 together. This current also flows through the coil of a second relay M which closes normally open contacts 15 and 17. The closure of contact 15 sets up a locking circuit, from line 14, through RB, R2 and M to line 16, thereby keeping contacts 15 and 17 closed until the reset button RB is opened. A second. effect of contact 15 is that contact 12 becomes directly connected to negative line 16 and thus current can flow from line 14 through contact 17, resistance R3, button T and through MR2 in the reverse direction to that which assisted the engagement of contacts 10 and 12 which now become separated. Contact 17 also allows current to flow through warning bulb 18 which remains illuminated irrespective of further temperature changes in the neighbourhood of the control source CS until button RB is pressed. de-energizing coil M. Testing.-The system can be tested by depressing button T and thus setting up a circuit from line 14, through RB, R5, the lower contacts on button T, through MR1 and CS which are in parallel with R1, through R4 to negative line 16. The small E.M.F. across MR1 thus set up operates the circuit as described above. Specifications 687,136 and 817.258 are referred to.