Abstract: Apparatus for indicating rate of ice accretion particularly for use in an aircraft, the apparatus including test surface on which ice forms in use. First and second gas conduits are supplied with gas from a common pressure regulator the inlet of which communicates with a gas supply. A control port of the regulator is supplied with a reference pressure signal and the regulator operates to maintain its outlet pressure at a predetermined amount in excess of the reference pressure. Each of the first and second conduits includes a restrictor and each conduit terminates at its end remote from the regulator in an orifice. The first orifice is adjacent the test surface and a pressure difference sensor is associated with the first and second conduits to produce a signal dependent on the pressure difference at points between the orifice and restrictor of the two conduits. The pressure difference signal is applied to an indicator.

Abstract: Apparatus for indicating the rate of ice accretion on a surface particularly for use in aircraft comprising a hollow housing divided internally by a resilient diaphragm into first and second chambers. A first conduit communicating at one end with a gas supply and terminating at its other end in a first orifice. Intermediate the ends of the first conduit is a first restrictor and the first chamber of the housing communicates with the first conduit intermediate the first orifice and the first restrictor. Movable relative to the first orifice is a test surface upon which ice can form in use. The test surface is in use moved at a known speed and at a constant spacing from the first orifice. A second conduit communicates at one end with the gas supply and at its other end terminates in a second orifice. Intermediate the ends of the second conduit is a second restrictor and the second restrictor is variable, the setting thereof being determined by the position of the diaphragm in the housing.

Abstract: Apparatus for indicating rate of ice accretion includes an endless test surface upon which ice forms in use. A gas flow passage terminates adjacent the surface in an aperture which is presented to and spaced by a known gap from the test surface. A flow of gas is generated in the passage towards the aperture and a drive arrangement drives the test surface past the aperture at a constant rate. An ice removal device is operable to remove ice from the test surface after the surface has moved past the aperture and there is provided a sensor which detects variations in the flow and/or pressure of the gas in the passage. These variations arise from the effect on gas flow of restriction of the gas by ice forming on the surface, and associated with the sensor is an instrument which provides an indication of the extent of the variation in flow and/or pressure and accordingly provides an indication of the rate at which ice is being accreted on the test surface.