Stand for the study of sensors based on thermocouples

Thermoelectric thermometers in aviation are used mainly to measure the temperature of individual parts of power plants and gas flows coming out of the engine jet nozzle. The principle of operation of a thermoelectric thermometer is based on the use of the thermoelectric effect. The phenomenon of thermoelectricity consists in the emergence of a thermoelectromotive force (thermoEMF) in the junction of two conductors made of two dissimilar conductive materials when there is a temperature difference between the junction of the conductors and their free ends. Such a circuit, consisting of two dissimilar metals, is called a thermocouple. Metal atoms make up a spatial lattice, inside which free electrons participating in thermal motion form an electron gas. The density of the electron gas is different for different metals. Because of this, there is a tendency to equalize the density of the electron gas at the contact point of two dissimilar metals. Some of the electrons move from one metal to another. At the same time, one metal is charged positively, the other negatively. A potential difference arises, which balances the difference in pressure of the electron gas. The contact potential difference does not depend on the shape and geometric dimensions of the thermoelectrodes and is determined by the temperature difference between the hot and cold junctions and the properties of the metal conductors of the thermocouple.

Stand for the research of resistive temperature sensors

Electric resistance thermometers are used in aviation to measure the temperature of oil and air inside and outside the cabins. The principle of operation of the resistance thermometer is based on measuring the electrical resistance of metals or semiconductors depending on the temperature.
The choice of material for a thermosensitive element is determined by ease of manufacture, reliability, sensitivity, a unique dependence of R(q) and the absence of environmental influence on the sensitive element. These requirements are met by metals – copper, nickel, iron and platinum, and semiconductors – chlorides and carbides; oxides of uranium, nickel, manganese, boron, silicon, germanium, tellurium, etc.
Temperature measurement in an electrical resistance thermometer is reduced to measuring electrical resistance, which can be carried out using a galvanometer, a logometer, or a compensation method.
In aviation on-board thermometers, bridge circuits with logometers are used as pointers. In such schemes, the deviation method is implemented.

Devices designed to measure rotation frequency are called tachometers. Tachometers are used to measure the rotation frequency of the engine shaft and its units. By the value of the rotation frequency, you can judge the traction and the dynamic and thermal stresses.

The magneto-induction tachometer is a remote device. Synchronous remote transmission consists of a three-phase alternating current generator (sensor) located on the aircraft engine, a three-wire line and a synchronous motor located in the pointer. The indicating device includes two units, which are mounted in one housing, a synchronous motor and a measuring system (tachometer).

Devices used to measure pressure in aircraft systems are called aviation manometers. They measure the relative pressure (overpressure). In aviation, manometers are widely used in the lubrication system of aircraft engines, in the fuel supply system of aircraft engines, in the hydraulic system of the aircraft, in the air and oxygen systems of the aircraft. Accordingly, they are called oil pressure gauges, fuel pressure gauges, hydraulic pressure gauges, oxygen pressure gauges, etc.
Aviation pressure gauges are mostly based on the method of comparing the force of the measured pressure with the elastic force of the sensitive element.

Manometers of the DIM type (remote inductive manometers) do not require the use of PMM (transmitting – multiplying mechanisms). This is ensured by the use of a differential inductive displacement converter. Manometers cover the range of measured pressures up to 30 MPa with pulsations up to 700 Hz.
Depending on the range of measured pressures, the PCHE (elastic sensitive element) of DYM type manometers are membranes or membrane boxes. The pointer is a magnetoelectric logometer with a moving magnet.

Vibration mainly occurs due to the presence of unbalanced centrifugal forces caused by the imbalance of the rotating parts of the engine. Destruction and increased wear of engine parts lead to increased vibration. Therefore, the amplitude of the engine vibration can be used to judge its technical condition.
Vibration parameters measured by devices:

· vibration displacement – displacement vibrometers;
· vibration speed – speed vibrometers;
· vibration acceleration – acceleration vibrometers.

Measurement methods: variable pressure drop, flow, tachometric, thermo-anemometric, ultrasonic. Engine thrust (power) and flight efficiency are determined by fuel consumption. Therefore, fuel consumption is measured with an error of no more than ± 2%.
Devices for measuring fuel consumption are called flow meters. Devices for measuring the amount of fuel consumed are called fuel quantity meters.
Turbine tachometric flowmeters and fuel quantity counters are most widely used in aviation. The principle of instantaneous fuel consumption measurement is to convert the speed of the fuel flow that passed through the sensor into the reading of the instantaneous fuel consumption indicator in kg/h. When the impeller rotates, the magnetic field of the permanent magnet of the impeller induces in the coils of the EMF sensor of variable frequency, which enters the frequency converter PCHN1T, where the frequency is converted proportionally to the flow into voltage. This voltage is compared with the reference stabilized voltage and with the help of a tracking system consisting of an amplifier USS2T , executive motor and run-out potentiometer, the arrow of the flow indicator moves.

Devices and systems designed to measure the volumetric or mass amount of fuel (oil) on board the aircraft are called fuel gauges. They provide:

· measuring the mass of fuel (oil) in individual tanks or groups of tanks;
· measurement of the total mass of fuel accounted for by each engine in the wing or aircraft;
· automatic control of the sequence of fuel production from the tanks and the sequence of refueling the tanks; – automatic control of fuel pumping to maintain the plane’s centering;
signaling about the presence of a critical fuel (oil) supply.
Float electromechanical and capacitive fuel gauges are most widely used in aviation. The principle of the capacitive fuel gauge is based on the dependence of the capacitor capacity on the level and dielectric constant of the liquid between the electrodes of the fuel gauge sensor.