Improvements relating to signalling transformer apparatus for use in dangerous atmospheres

摘要

700,911. Transformer arrangements. DAVIS & SON DERBY, Ltd., J.. and DAVIS, W. H. Oct. 10, 1951 [July 10, 1950], No. 17146/50. Classes 38 (2) and 38 (4) A signalling transformer apparatus of the intrinsically safe type (as defined in British Standards Specification 1259:1945) has a small wattage indicator lamp 15 connected directly across the secondary winding of the transformer and which is visible through a window in the flame proof casing 13 of the apparatus, the lamp being so arranged that the current which it consumes does not reduce the intrinsically safe output available from the transformer for signalling purposes. The intrinsically safe output is taken from terminals 12, 12a, the secondary winding in series with a current limiting resistor 17 being connected between these terminals. A terminal board 20 may be arranged to carry the indicator lamp ; the resistor 17 may also be wound thereon. Thus a failure is indicated without unnecessary opening of the flame proof casing.