An ice detector is an optical transducer

Transducer

A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...

 probe available for aviation

Aviation

Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

 purposes. It has no moving parts

Moving parts

The moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....

, is completely solid and its principle of operation is entirely optical. Intrusive to the airstream and hermetically sealed

Hermetic seal

A hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...

, it uses un-collimated light

Collimated light

Collimated light is light whose rays are parallel, and therefore will spread slowly as it propagates. The word is related to "collinear" and implies light that does not disperse with distance , or that will disperse minimally...

 to monitor the opacity

Opacity (optics)

Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

 and optical refractive index

Refractive index

In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

 of the substance on the probe. It is de-sensitized to ignore a film of water.

The device works as a combined optical spectrometer

Spectrometer

A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...

 and optical switch

Optical switch

In telecommunication, an optical switch is a switch that enables signals in optical fibers or integrated optical circuits to be selectively switched from one circuit to another....

. A change in opacity registers as rime ice

Rime (frost)

Hard rime is a white ice that forms when the water droplets in fog freeze to the outer surfaces of objects. It is often seen on trees atop mountains and ridges in winter, when low-hanging clouds cause freezing fog...

. A change in refractive index registers as clear ice. Optical components are made of acrylic glass

Acrylic glass

Poly is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. It is sometimes called acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate...

, which is the material used for aircraft windshields. The wavelength

Wavelength

In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...

 of the transducer's excitation light is not visible to the human eye so as not to be mistaken for any kind of navigational running light.

Installation

Optical ice detectors can be installed on any type of air vehicle with enough air speed to keep water from accumulating on the optics, such as rotorcraft, general aviation aircraft and unmanned aerial vehicles. They can be embedded into host aerospace systems such as an altimeter

Altimeter

An altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.-Pressure altimeter:...

, antenna, anti-icing system, flight data recorder

Flight data recorder

A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...

, jet engine inlet, pitot tube

Pitot tube

A pitot tube is a pressure measurement instrument used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot Ulo in the early 18th century and was modified to its modern form in the mid-19th century by French scientist Henry Darcy...

, stall warning indicator or weather system.

Optical ice detectors operate on 3.3 V DC at 100 mA. Installation requires the probe to be mounted in the airstream beyond the boundary layer

Boundary layer

In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...

, and in a location easily accessible to the pilot for occasional cleaning with a cotton swab and isopropyl alcohol

Isopropyl alcohol

Isopropyl alcohol is a common name for a chemical compound with the molecular formula C3H8O. It is a colorless, flammable chemical compound with a strong odor...

.

Operation

The device works as a rudimentary go/no-go ice indicator or as an icing rate indicator for pilots who may have inadvertently entered icing domains.

Electronic signal-level comparator

Comparator

In electronics, a comparator is a device that compares two voltages or currents and switches its output to indicate which is larger. They are commonly used in devices such as Analog-to-digital converters .- Input voltage range :...

s sense the transducer's output and activate LED

Light-emitting diode

A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

s to indicate relative icing rates to the pilot. The pilot can then judge the rate of ice accumulation and make a piloting decision. Once the aircraft has left the icing region, the ice either ablates or melts and blows away. The icing rate display sequence then reverses itself.

Transducer probe de-icing can be hastened by incorporating turns of resistance wire and dissipating a few watts into the probe, which weighs ¼ ounce. This resets the transducer in anticipation of the next icing event.

Optical ice detectors offer substantial adjustment range of drive level and returned signal amplification. Thus, they can be applied to operate in a wide variety of applications and sensitivities, down to 0.001" of ice.

Testing

Testing at NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 Glenn Icing Research Tunnel in Cleveland, Ohio

Cleveland, Ohio

Cleveland is a city in the U.S. state of Ohio and is the county seat of Cuyahoga County, the most populous county in the state. The city is located in northeastern Ohio on the southern shore of Lake Erie, approximately west of the Pennsylvania border...

, has verified the performance of optical ice detectors.
reference: NASA Lewis (Glenn) video document D040 dated 23 September, 1997, range time = 18:43:37 hours

Other types

Other types of ice detectors for aircraft include:

• acoustic - registers changes in the sound wavelength when icing occurs
• nuclear - registers changes in emission level when icing occurs between source of radiation and the sensor