GB665291A - Apparatus for detecting the occurrence or approach of icing conditions - Google Patents

Abstract

665,291. Temperature alarm systems. NAPIER & SON, Ltd., D. Jan. 9, 1940. [Jan. 19, 1949] No. 1489/49. Class 118 (i). [Also in Group XXXIII] Apparatus for detecting icing conditions and operating warning or other apparatus comprises a first relay device controlled by an element which operates when the atmospheric temperature approaches freezing point, a heated element situated in an air stream, and a second relay device which operates on a pre-determined rate of temperature drop of the heated element, or when the difference in temperature between the heated element and the atmosphere falls below a predetermined level, and warning or other apparatus which operates when both relay devices are operative. The apparatus may be used to prevent ice formation on aircraft. In Fig. 1, element A which is subjected to atmospheric air temperature, is associated with .thermocouple B and amplifier B<SP>1</SP> so that when the temperature of A approaches or falls below freezing point, relay B3 is operated. Air also impinges on heated element E, associated with thermocouple F and amplifier F<SP>1</SP>, the output of which is applied to coil F3 tending to keep relay D non-operated. A further thermocouple C is associated with element A, the amplified output of which is applied to coil C3 tending at operate relay D. The arrangement is such that relay D operates when the difference in temperature between elements A and F falls below a predetermined level. Relay G1 is controlled by the contacts of relays B3 and D so that it operates when the atmospheric temperature approaches freezing point, and also the heated element F is sufficiently cooled relative to the atmospheric temperature, a condition which depends on the amount of water vapour present in the atmosphere. Relay G1 may control a warning device G3, and de-icing apparatus by means of a further relay G4. Temperature responsive electrical resistances may be used instead of thermocouples. In an alternative arrangement (Fig. 2), a heated element K, situated in the air stream, and the resistance of which depends on temperature is connected in a bridge circuit L, which self balances on receipt of an impulse from relay contacts N<SP>1</SP>. An output from the bridge circuit proportional to the degree of unbalance, and which is therefore reduced to zero by each impulse from N<SP>1</SP> is applied via amplifier M,, cam contacts O and rotary switch Q to valve T which controls the firing of thyratron valve U in the operating circuit of relay H5. Relay H5 thus operates when the fall in temperature of element K in the period between two impulses exceeds a predetermined amount, a condition which arises when an atmosphere containing water droplets is encountered. Relay H1 is controlled by means of a thermocouple and amplifier so that it operates when the temperature of element J1 approaches freezing point. The warning device H3 and main relay H4 controlling de-icing apparatus are energized when both relays H5 and H1 are operated. Rotary switches Q and R 'which control impulsing relay N<SP>1</SP> are step-by-step operated by means of cam operated contacts P. Reference is made to Specification 662,540, [Group XI], regarding the nature of the elements J<SP>1</SP> and K.