Carburettor Air Essay
The utilisation of these various methods provides us with a very convenient means of classifying temperature – measuring instruments. The majority of these instruments currently in use are, however, of the resistance and thermoelectric type and are applied to the measurement of the temperature of such liquids and gases as fuel, engine lubrication Oil, outside Air, Carburettor Air and turbine gas exhaust. The monitoring of Oil and Fuel temperature on an aircraft is an essential operation mainly due to the environment and conditions that it is subjected to, not just in flight, but also on the ground as well.
Other affects that this variable could have upon the aircraft would be to hinder performance, lessen flight ranges, and endanger passengers and crew due to high explosive and flammable risks. For Fuel Temperature a resistance thermistor temperature transducer is used. This type of transducer is a temperature sensitive resistor indicates changes in the resistance. The resistance of the thermistor decreases as the temperature increases. Below is a Schematic arrangement of a temperature sensor. The bulb acts as a safety barrier of protection around the coil assembly.
The coil is wound at the bottom end of the former only. This ensures that the coil is well immersed into the hottest part of the liquid, minimising the errors due to radiation and conduction losses in the “bulb” which gives a more accurate reading. A Balancing coil is provided so a standard temperature / resistance characteristic can be obtained. This allows for any deviations in the characteristics of the coil. These types of transducers, thermistor’s are mainly constructed from semi – conductive disc’s or beads, which are enclosed in vitreous enamel or in glass envelopes.
Due to the efficiency of these the feedback response is extremely rapid. For this application either of the options for a display could be used, Analogue, Digital or a Cathode Ray Tube. But I have chosen the digital display for reasons that are described in that section (see display units) OIL PRESSURE In many of the systems associated with the operation of aircraft and engines, liquids and gases are used the pressures of which must be measured and indicated. Pressure is measured by instruments systems, which in the majority of applications are of the remote indicating type i.
e. their sensor transmitter units, are connected, to a pressure source. Which pass data through an electrical transmission circuit. Which are connected to indicators. On jet aircraft a capsule system is used. This system would use a resistive transducer, the output could be sent to a conditioning device such as a Wheat stone bridge, this would record maximum output which could then be sent directly to a reading device or could be further conditioned before displayed in the cock pit. ADC
Analogue to digital converter, converts a continuous analogue signal produced by a digital (off and on) signal for computer processing. This is an electronic circuit that converts an analogue signal to a digital output. Such a circuit is required to convert the signal device to a digital signal for input into a computer. For example many sensors designed to measure temperature and pressure, produce an analogue signal in the form of voltage and this must be passed through an ADC before computer input and processing.
For signals of digital to analogue output, the process is therefore reversed. WHEATSTONE BRIDGE – Measure an unknown resistance The Wheatstone Bridge is an old system yet it is still applied to temperature indicators used in some types of aircraft. The most appropriate system to use in this case would be the Radiometer system. The Radiometer system employs two coils moving in a permanent magnetic field, the circuit is formed so that the current supplied to the two coils is in opposite directions, the movement of the coils is proportional to the current that they are supplied with.
The direction of the movement of the measuring element is dependent upon the flow of the current. BACKGROUND INFORMATION – Theory of the Wheatstone Bridge A current flows in an electrical circuit driven by the potential difference at a battery. Resistance, current and voltage are connected by Ohm’s law. U = I x R The current and potential difference (= measured voltage) in each part of the circuit can be calculated with the help of Kirchoff’s rules. 1. The sum of the potential drops around any circuit loop must equal the sum of the potential increases.
2. At a junction point in a circuit where the current can divide, the sum of the currents into the junction must equal the sum of the currents out of the junction. Look at the following set-up: When the transducer feeds information through into the conditioning element it is being converted into a signal that can be represented by the display unit. If that conditioning element happened to be a Wheatstone Bridge then the output to the display would be of a higher degree of accuracy due to the resistance measurements.
University/College: University of Arkansas System
Type of paper: Thesis/Dissertation Chapter
Date: 13 July 2017
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