SU993157A1 - Device for measuring non-uniformity of thermoconverter amplitude frequency characteristics in infrasound range - Google Patents

Description

of the known device is the low resolution and accuracy of determining the non-uniformity of the amplitude-frequency characteristic due to the frequency non-uniformity of maintaining the level of current flowing through the thermal transducer under investigation, which is This is due to the frequency non-uniformity of the electrodynamic comparator. The purpose of the invention is to improve the loudness and accuracy of measurements. The goal is achieved by the fact that, in a device for measuring irregularity of amplitude-frequency characteristics of thermal converters in the infrasonic frequency range, containing a tunable generator and low-pass filter, the input is connected to one of the input the device’s terminals, two measuring thermocouples, two potentiometers, two potentiometers, a resistor, a zero-indicator, a test signal generator and an adder, are introduced. Exit tunable oscillator connected to one of vhodbv adder and the first input terminal of the first; The measuring thermoconverter has a second input terminal which is connected to the device body, the output of the test signal generator is connected to the second input of the adder not: the first input terminal of the second measuring thermoconverter, the second input terminal of which is connected to the device body and to one. its output terminals, and the second output terminal of the above-mentioned thermal converter is connected to the first output terminal of the first measuring thermal converter, the second output terminal of which is connected via the first potentiometer to the device body, and the mobile terminal of the latter is connected to one of the inputs of the zero indicator, the second input of which connected to the movable output of the second potentiometer, the first output of which is connected to the output of the low-pass filter, and the second output through a resistor connected to the device, the output of the sums Ator is connected to the second input terminal of the device. FIG. 1 shows a block diagram of the device; in fig. 2 time diagrams of voltages for the operation of the device. In the drawing, the following voltage designations are accepted: U and Uj at the outputs of the tunable -generator 1 and the generator of the test signal 2; voltage Id at the output of the adder 5; the voltage C ptcn the output of the thermoconverter under investigation 10, caused by the input voltage, the voltage and the infrasonic frequency at which the deviation of the amplitude-frequency characteristic is determined; UTTTJI voltage at the output of the thermometer 10 under study, which would have occurred if U had a voltage at its input. The device contains a tunable generator 1, g, 2 generator of the test signal, measuring thermocouples 3 and 4, adder 5, made according to the scheme a large-scale amplifier on an operational amplifier b and resistors 7–9, a thermocouple under study 10, a low-pass filter 11, potentiometers 12 and 13, a resistor 14, a zero-indicator 15. and input terminals 16 and. 17 devices, the device works in the following way. Equal in magnitude output sinusoidal voltages U, -, and U of generators 1 and 2 are respectively supplied to the inputs of measuring thermocouples 3 and 4. Since the voltages UjjH Uj are selected within the audio range, 3 and 4 are constant at the output of each voltage, proportional., to the square of the effective input voltage, i.e. from Kz and U4. K. and I where and are the constant voltages at the outputs of the thermal converters 3 and 4; Kg and K are the conversion factors of thermal converters 3 and 4. The sum of constant voltages and from sequentially and according to the included outputs of thermal converters 3 and 4 is fed to the input of potentiometer 12. With the characteristics of thermal converters 3 and 4 being identical. In this case, the input voltage of the potentiometer 12 is a constant voltage, equal to and $), (.3) from -U4 where and is the total constant voltage on the series-connected outputs of the thermocouples 3 and 4 f Co-conversion factor of the thermocouples 3 and 4. The part of the indicated voltage Id is applied to one of the inputs of the null indicator 15. Analog adder 5 serves to sum the voltage 1) and Uj supplied to its inputs. The output voltage IJj-i of the shock-absorber 5 is fed to the input of the thermal converter under study 10. The output voltage of the thermal converter 10 is fed through the low-pass filter 11 to the series connection of the potentiometer 13 and the resistor 14. The constant voltage taken from the average potentiometer 13 is supplied to the second input is zero of indicator 15. The infrasonic frequency voltage at which the frequency response deviation is measured. is formed from the sum of two equal amplitude harmonic voltages with frequencies differing by two times the infrasonic frequency of the ori input to the thermocouple input 10 of the total voltage Uj and sin uj t UwnSin Ы2 t, where Um Uffln is the voltage amplitude; to and jrt2 are the frequencies of the voltages U, respectively. The differential equation of the thermal state of the heater of the thermal converter has the form; “- I sinAu tJ R: where) t + IwnSinM a El is the instantaneous value of the current proportional to the voltage Ujj; . (instantaneous value of currents proportional to components of voltage Uj-; .;jj - overheating temperature of the heater when current is passed through it R - heater resistance; H - heat transfer coefficient; m - heater mass; c - specific heat capacity of the heater material; SL- is the frequency at which the frequency response is measured. For a steady-state thermal mode, the solution to equation (4j is: (d) (W.-co) 1-X - (2). 5in (u ,,. u, 2 ) i .-; j. ± -.Cos (u ,, u, .Jt, (5) where 4i arctg J / Zui, for arctgl / Zu -; - is the heat constant of the heater time. Considering the stipulated condition, I and Ved aanyunu), „,, W.-Yud, 2i1s (.), trigonometric transformations The equation (5J takes the form: 2„ 2 5 "n (2ts, + H; Stn (2u i-Kf2J + mi-mo“ 1+. "Sin (2u; cpt44) / (s) GDE c arctg T / Sistr. Since the frequencies U) and uig are chosen in the sound range, and the constant vmeni i thermal converter is from tenths to units of seconds, it is easy to provide such the choice of frequencies w and uj g under which the conditions are fulfilled, uigt, (7J With regard to the fulfillment of conditions (7), equation (6) becomes simpler and takes the form -, -, „E„ 3 R .M ЗМ + -рЗ% 5ш (2Я1 + FG ElvcT V l З / fWl + 4§t42. , (.., (o) From (8) it is IMPORTANT that the temperature of the heater, and hence the thermoelectromotive force at the exit of the thermogunifier, contains a constant and variable components, i.e.

V

/

Sin (2uJ ,,)

gn

T

vgch © .-. + e,

(9)

Esr

OVCT De ed - (1. 1)

BY)

- average temperature of the heater; Condition constant component;

wg, Imp Int sin (2 t-K |). (П) нУ1-Ь4 «2г: гi-j I J

- variable temperature component per 1T) evatel.

As can be seen from expression (10), the constant temperature component of the heater's thermal converter, when connected to it, the voltages U and Uj is equivalent to the connection of a voltage source with parameters equal to t + I 2 hp ° t mg -. f, and ГП -П m The evaluation of the dynamic mode of the thermal converter 10 for the cases of connecting the voltage Uj to it can be made by the ratio of the variable component of the temperature of the heater to its average value. For the case of connection to the thermocouple, the voltage generator 10 is expressed. lower C10J. and (11) follows (+ F) .JJ / f C-J “-il / C + -tfni L-- t. ./ i, (, 4JF After the T-pp values are created when the voltage is created are the same, even taking into account the possible relative amplitude instability of the generator 1 and 2, you can write the following approximate equality: l2 + i2 m -1 1 PP2 m-1 mg For example , if I and Irni differ by 3%, this equality is provided with an error of no more than 0.05%. Therefore, taking into account (15), expression 14 takes the form sin (252 t + F) (16) С Ср 1 (1 + ч- SC t From the expression (16) it can be seen that the dynamic mode of the thermoconverter 10 is the same as for the case when the sum of voltages of different parts is supplied to it from the UE, and for the case of supplying a single voltage of an infrasonic frequency to the thermocouple. (1) In the output voltage of the thermoconverter under study 10, depending on the frequency difference uj of the generators 1 and 2, a variable component (. Expression (11)) is contained, corresponds to the case when the frequency 57 belongs to the infra-sound range or the variable component may be absent if the frequency is within the audio range (expression 10). The case in which I. is within the sound range, i.e. beats / arising from the flow of currents s and ujj through the heater of the thermoconverter under study 10, occurs with an audible frequency (the Gt-10 transducer with this works in a static mode), is used during the calibration of the proposed device. To calibrate the device, potentiometer 13 preliminarily calibrated in relative units (. Expression (2) J. is set to a position that is conventionally taken as zero. This position corresponds to the zero deviation of the amplitude-frequency characteristic, i.e. corresponds to the conversion factor of the thermocouple converter 10 on selected as the reference frequency Slg. The frequency is set in accordance with the conditions “о” Ш2, which provides the beats of the frequencies uj and u) 2 generators 1 and 2 in the sound range, i.e. provides a static operating mode of the thermocouple 10. After this, using a potentiometer 12, a zero indicator of the indicator 15. is obtained. To measure the amplitude-frequency characteristic deviation of the investigated thermoconverter at the infrasound frequency, the frequency of the oscillator 1 is set to 5, it satisfies 5 the condition (jo - W2 251. In this case, if there is an imbalance of the null indicator 15, which indicates the amplitude-frequency non-uniformity of the conversion coefficient of the thermal conversion, l 10, using a potentiometer 13, set the null indicator to zero 16. The deviation of the transducer coefficient 10 at a frequency 52 relative to its ratio was transmitted at the reference frequency Yar determined by the position of the slider of the potentiometer 13, which is calibrated in relative units (for example, in percent) By registering with the help of the null indicator 15, the equality of direct voltages at the outputs of potentiometers 12 and 13 can be represented by the expression (3) in the form (U t U) K, (U, Uj). . R-Gh R + rv where the transfer coefficient of potentiometer 12; KK is the conversion coefficient of the thermoconverter under investigation 10; (Ux, + U2) is the average value of the voltage at the output of the thermoconverter under study 10, separated by a low-pass filter 11;

K, G is the resistance of the resistor 14 and the potentiometer 13, respectively, g R RG is the resistance between the middle and lower positions of the potentiometer 13.

For simplicity, the transfer ratio of the adder 5 and the lowpass filter 11 is assumed to be one.

Since the sinusoidal voltages and /, and u2 are different in frequency, the value (U2J represents co6ojft the sum of the squares of their effective values, i.e.

(. and) and + and

L19j

.g

, In view of (19), expression (B) leads to the form

„K“ .KMR d)

120)

R gh

Dependence of the relative deviation of the conversion coefficient at a given frequency S2 nq relative to the coefficient. the conversion at the reference frequency 5g from the change in resistance of the potentiometer 13 is determined from the expression (20) and has the form; H1L TGy) R + r, 0 where-p is the relative deviation of the conversion coefficient of the thermal converter 10 at the frequency I. with respect to the conversion coefficient at the frequency SZ n, is the change in resistance between the middle and lower extreme terminals of the potentiometer 13, corresponding to the relative deviation of the conversion coefficient LKu / Kxj g - resistance between the middle and lower extreme terminals of the potentiometer 13, corresponding to the conversion coefficient at the frequency .5. The conversion factor K (K measuring thermocouples in the expression (iJO) is a constant value. This is due to the fact that to obtain the required mlx values And the tuning range of generator 1 is one percent. (Expression (17)). In such a narrow frequency range, the conversion factor of the thermal converter 3 is almost constant. The constant conversion coefficient of the thermal converter is also 4, since it operates at a fixed frequency u) 2. As can be seen from the expression (21), the calibration characteristic of the device is almost linear, which allows to ensure high accuracy of the measured value read directly from the position of the slider of the calibrated potentiometer 13. Since the low-frequency irregularity doesn’t exceed several percent, the resistance of the potentiometer 13 is not chosen less than a dock

less resistance of the resistor 14. This ensures low attenuation of the output signal of the thermocouple under study and a small reading error of the measured value.

From expressions (20) and (21), it can be seen that the measured relative deviation of the conversion coefficient of the thermoconverter under study at a given frequency does not depend on QT.

Claims (2)

1. Measuring equipment, 1963, No. 2, p. 34 2. Beznikovich A.Ya. and Gravin, ON, Investigation of Multielement Thermal Transducers, - Proceedings of the Institutes of the State Committee, no. 82 (142j, M-L., One hundred "darts, 1965, p.112, SprotiotyU. / I Vb / " /: 7 / 7X u chu