GB1071752A - Ice condition detecting device - Google Patents

Abstract

1,071,752. Ice-detecting apparatus. HOLLEY CARBURETOR CO. July 9, 1964 [March 30, 1964], No. 28349/64. Heading G1N. A device for preventing the formation of ice on a surface compares the output of a device measuring saturation temperature with that of a device measuring the temperature of the surface and operates a heater when the first exceeds the second provided also that the surface is near to freezing point. The basic system is shown in Fig. 1. An A. C. -fed capacitor (see below) feeds a signal proportional to absolute moisture content and hence to saturation temperature of the air to a gate circuit 24. This circuit is also fed with the output of a surface temperature measuring thermistor 28 which opens the gate only when surface temperature is approaching freezing point. If it is, both outputs are fed after suitable rectification and amplification to a differential amplifier 32 which compares them and, if surface temperature is lower than saturation temperature, operates a relay to switch on a surface heater 62. In an elaboration Fig. 10 (not shown) a further condenser is incorporated which responds to the presence of free water (e.g. rain) and if the surface temperature is near freezing, overrides the saturation temperature measuring device to switch on the heater. This free water sensor may also operate to keep water out of the moisture sensor. The saturation temperature sensor Fig. 2 (not shown) consists of a cylindrical capacitor having outer and inner electrodes 66, 70 between which is sandwiched an intermediate sensitivity grade of polyvinyl alcohol called Elvanol. This material is said to acquire a surface film of moisture which varies the capacitance to give an indication of absolute moisture content. The outer electrode is perforated to allow the moisture to reach the dielectric and a cone 110 guides the air flow into axial passages around the electrode. To maintain the temperature of the detectors above dew point a central heater is provided and a thermistor is embedded in an epoxy resin filled cavity in the inner electrode. In further arrangements. Figs.6-9 (not shown) the inner electrode is also perforated and when no longitudinal air flow is provided the air enters the assembly through the circumferential walls of the housing and an arrangement is also described in which the air flows over flat electrodes plates which are adjustable to and from each other. The entire sensor may be situated in a heated housing Fig. 11 (not shown). Free water sensor this consists of a pair of electrodes with an intermediate dielectric as already described but the electrodes are spaced from the dielectric to allow free water to flow through and the dielectric to dry off.