RU2005300C1 - Method of measurement of speed of gas flow and device for its implementation - Google Patents

Description

the voltage applied to the measuring bridge, in which two side thermistors are connected, is maintained constant). In contrast to the prototype, the inventive method also allows one to limit it to implementation by only three thermistors thermally insulated from the housing and in good thermal contact with the gas medium. This ensures that the hot-wire anemometer is insensitive to changes in the temperature difference between gaaa and the substrate body, which increases the accuracy of measurements and the stability of its operation.

This goal is achieved in that in a device for measuring the gas flow velocity containing the first, second (central), third thermistors and an electronic signal processing circuit including four operational amplifiers and resistors, the first terminals of the first, second and third thermistors are connected to a common the bus, and their second terminals are connected to the first terminals of the first, second and third resistors respectively, the second terminals of which are interconnected, the second terminal of the central thermistor is connected to non- to the rotating inputs of the first and second operational amplifiers, the second outputs of the first and third thermistors are connected to the inverting inputs of the first and second operational amplifiers, in the first and second operational amplifiers, the inverting inputs are connected to the outputs through the fourth and fifth resistors, respectively, the outputs of the first and second operational amplifiers are connected to the inverting input of the third operational amplifier through respectively the sixth and seventh resistors, non-inverting the input of the third the operational amplifier is connected to a common bus, and its inverting input through a capacitor is connected to its output, the output of the third operational amplifier is connected to a common connection point of the first, second, and third resistors, the output of the first operational amplifier is through the eighth resistor, and the output of the second operational amplifier is through the ninth a resistor is connected respectively to the non-inverting and inverting inputs of the fourth operational amplifier, the non-inverting input of the fourth operational amplifier through the tenth the resistor is connected to the common bus, and the inverting path through the eleventh resistor is connected to its output.

In FIG. 2 is a schematic diagram of a device.

The device contains a central 1 and two side 2 and 3 thermistors, which are part of the hot-wire anemometer, constant resistors 4-14, operational amplifiers 15-18, s as well as a capacitor 19. Thermistors 2. 1, 3 with ratings RTI, Рта. The terminals are respectively connected to fixed resistors 4,5 and 6 with ratings R1, R2, R3 and form three voltage dividers. Operational amplifiers 15 and 16 with feedback resistances 7 and 8 having R4 ratings. R5, connected to three voltage dividers. The outputs of the operational amplifiers 16 and 15 are connected to a summing integrator formed by the operational amplifier 17. Resistors 9 and 10 with ratings R6 and R7 and a capacitor 19 C. The outputs of these amplifiers are also connected to a subtracting amplifier based on the operational amplifier 18 and constant resistors 11,12 , 13 and 14 with ratings R8, R9, R10 and R11 respectively.

Maintaining a constant temperature difference T2 - (I + TK) / 2 with the help of a summing integrator (provided that R6 R7) occurs as follows. When setting up the circuit, the ratio R2 / R1 Ri2 / RTI is established, which leads to the formation of voltages U1 0. U2 0. An integrator that sums the voltages U1 and U2 generates a positive voltage U. With an increase in U, thermistors are heated and a temperature profile appears, shown in FIG. 1. In this case, the temperature difference T2- - (T1 + TK) / 2 increases. At a certain value of U, the condition

Ita. g „/ t. Ti + Tz

Yam

 exp {a (T2

ch (a

Tz

Ti v R2 - -TGG

) D 0)

as a result, the sum of the voltages U1 + U2 О. Subsequently, condition (1) is automatically maintained during measurements at a constant ratio of powers dissipated at the central 1 and two side 2 and 3 thermistors. If the temperature difference TK - T1 does not exceed several degrees, then the value (TK - T1) / 2 «1 (oZ). In this case, equation (1) is reduced to

Т2- (Т1 + ТЗ) /2-1..п - 2Г. Нте -const (2) The output voltage of the device, formed by a difference amplifier with a gain K, is equal to (taking into account equation (1))

iW-K- (U1-U2) -2KUx

72005300 8

xR 2 R 4 thfg (h) of micromechanical structures on silicon, R 1 (R 2 + Ri2) 2) allowing the creation of film thermistors on thin dielectric films Pri- (TZ-T1) / 2 "1k, hanging over the recess in I,, , c R 2 R 4 5 silicon substrate. Films with an area of willow UR 1 (R2 + RT2). ) () 0.01 ... 0.1 mm2 have contact with the substrate

only in certain areas around the proposed device allows a meter recess, and their thickness can be extend the measuring range to less than 1 micron. Design data at high speeds. An increase in the heat transfer of the sensitive element and the powder at high flow rates, which the thermal conductivity of the films should lead to the cooling of thermo- (less than 0.02 W / cm K) provide non-thermistors, is compensated by an increase in the exceptionally high thermal ieol - of the dissipated power due to an increase in the thermistors from the substrate, but also their voltage U. In this case, an increase in U with a small mass and good thermal contact leads to an additional increase in the sensing gas. For this reason, the spit of the device, since the night thermistors located the output voltage, which is determined by the equation of the dielectric film, have speeds (3) and (4), proportional to the influence of about 5 ms, which allows them To U.20, monitor the change in gas temperature,

The proposed method is expedient and their temperature is practically independent of the use in highly sensitive thermo-temperatures of the substrate, anemometers, the thermistors of which have high thermal insulation from (56) US Pat. No. 4,542,650, cl. G 01 F 1/68. corps. For the manufacture of such ter-25 1985.

MoNemometers are currently US Pat. No. 4,548,078, cl. G 01 F 1/68, 1985 Forming Technology is available.

l

Claims (1)

The claims of the first and second operational gain. By measuring the gas velocity of 30 lei, the second terminals of the first and third flows, consisting in heating the centrifugal thermistors, are connected to the inverted thermistor and determining the first and the gas flow velocities by the difference of the second operational amplifiers, in the two side thermistors, PTO and second operational amplifiers x characterized in that the additionally 35 inverting inputs are connected to the output heat two side thermistors, through each quarter and at the same time, the ratio of power dissipated by the resistors, the outputs of the first and second on the central thermistor, to which operational amplifiers are connected to the total power dissipated by the inverting input of the third operation, two side thermistors, and also the amplifier through the corresponding difference between the temperature of the central sixth and seventh resistors, a non-inverted thermistor and the average temperature input of the third operating temperature of the two side thermo-resistors, the heater is connected to a common bus, and it kept constant. 45 inverting input through capacitor 2. A device for measuring speed with its output, the output of the third operating gas stream containing the first, second, amplifier is connected to a common swarm point. third thermistors and electronic connections of the first, second, and third signal processing circuitry. resistors, the output of the first operating amplifier including four operational amplifiers; 50 Amplifier through an eighth resistor, and the output of bodies and resistors, characterized in that the second operational amplifier - through the first outputs of the first, second, and third ninth resistors are connected to the corresponding thermistors are connected to a common indirectly to a non-inverting and inverting-bus, and their second terminals are connected to the Y input ° Dam of the fourth operating room with the first terminals respectively the first 55 amplifier, non-inverting the input of the four-; of the second and third resistors, the second of the operational amplifier through the des - pins of which are interconnected, the second resistor is connected to the common bus, and the second terminal of the central thermistor-inverting input is connected to the non-inverting inputs of the resistor through its eleventh output. t F I .. / l about FIG. 7