GB775013A - Improvements in or relating to apparatus for detecting the formation of ice on a surface - Google Patents

Abstract

775,013. Electric indicating and control systems. BRISTOL AEROPLANE CO., Ltd., OMBRAIN, G. L. D'., and MACINTYRE, J. M. April 19, 1955 [Feb. 23, 1954], No. 5262/54. Class 40 (1). [Also in Groups XXXIII, XXXIX and XL (c)] Apparatus for detecting ice formation on a surface comprises a vibratable element located for subjection to the same conditions as the surface, means for maintaining the element in a state of free vibration, and means for producing an electricl potential which varies in response to an increase in the frequency of vibration of the element and thus to an increase in the thickness of ice thereon. In Fig. 1, the element is a diaphragm 3 flush with the surface, vibratable by a coil 6 on a core 5. A rod 15 of non-magnetic material has a permanent or electromagnet 16 at one end and is secured to the diaphragm at its other end, so that vibration of the diaphragm results in a signal in a pick-up coil 9. This coil is connected through leads 10, 11 to the input of a triode 22, which feeds a second triode 23 through a phase shift network 26. A transformer 25 in the anode circuit of triode 23 has one secondary winding 24 connected through leads 7, 8 to coil 6, so that the diaphragm acts as the resonant frequency determining element in the oscillator circuit of triodes 22, 23. The other secondary winding 30 of the transformer 25 feeds a frequency discriminating bridge (see Group XL (c)) coupled to a magnetic amplifier 41, the D.C. output of which is fed to an indicator 50, so that an indication is given of the sense and magnitude of the departure of the resonant frequency of the diaphragm from a reference frequency, which is chosen as that of the diaphragm free from ice. Ice formation is stated to raise the resonant frequency, and liquid or mushy deposits to lower it. In Figs. 3 and 4 (not shown) alternative frequency discriminators are shown, and a three-phase transductor may replace the magnetic amplifier. The output may control current to heating elements in the surface and near the vibrating element, or may control the supply of hot gas or a liquefying agent for deicing.