RU2568972C1 - Device to determine dynamic characteristics of temperature detector - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device comprises serially connected a unit (1) of formation of stepped impact of temperature at a temperature detector with temperature and signal outputs, a temperature detector (2), a measuring converter (3), a subtracting unit (4), a unit (5) of signal conversion from a temperature detector into an attenuating pulse signal and a spectrum analyser (6). The second input of the subtracting unit (4) is connected to a controlled source (7) of a permanent signal level. The signal output of the unit (1) of formation of stepped impact of temperature at the temperature detector is connected to the second input of the unit (5) of signal conversion from the temperature detector into the attenuating pulse signal.

EFFECT: increased accuracy of determination of dynamic characteristics of a temperature detector due to production of amplitude spectrum of a signal generated in a device and related to sought characteristics.

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Description

The invention relates to instrumentation, in particular to methods and devices for testing or calibrating temperature measuring devices (temperature sensors), mainly temperature sensors for gas and air flows.

A device is known (USSR author's certificate 1012049, IPC G01K 15/00, publ. 04/15/1983, Bull. No. 14) - [1] for measuring the transfer function of a thermal converter, containing a memory block where the voltage is proportional to the signal from the thermal converter to its transferring to a medium with a lower temperature, a resistive divider, the output of which is set to a voltage with a 50% and 90% level from the voltage recorded in the memory block, two comparison units, consisting of their zero-organs, logic elements, generators and counters s pulses measuring the time intervals t ₉₀ and t ₅₀ from the beginning of the transient until the thermocouple output signal, respectively, its 50% and 90% of the initial level, and three additional memory blocks with the blocks of digital reference with recorded at previously calculated coefficients table (time constants ) second-order transfer function depending on the values of t ₉₀ , t ₅₀ and t ₉₀ / t ₅₀ .

However, the known device does not allow to determine the dynamic characteristics of the thermocouple, if its transient is required to be described by the sum of more than two exponential components to increase the accuracy of determining the dynamic characteristics.

A device is also known (USSR author's certificate 1024750, IPC G01K 15/00, publ. 06/23/1982, Bull. No. 23) - [2] for determining the dynamic characteristics of measuring transducers of a non-electric parameter, mainly temperature, containing a block for the formation of the acting parameter, temperature outputs which are connected to the inputs of the signal shaper of the acting parameter and the investigated measuring transducer, the outputs of the latter are connected to the recording unit, a two-channel amplifier located between the recording unit and a computing unit, two comparators, the inputs of the first of which are connected to one of the outputs of the computing unit and one of the outputs of the memory unit, and the inputs of the second comparator are connected to the second outputs of the computing unit and the memory unit and to the outputs of two signal extraction units, the inputs of which are connected to the outputs the first comparator, and an indication unit connected to the output of the second comparator.

The signal generator of the acting parameter in the known device is designed to create a signal in the form of a pulse and performs the function of the signal output of the block forming the acting parameter, which signals the beginning of the impact of a temperature jump on the measuring transducer.

The principle of operation of the known device consists in generating, according to the program, from the transient response of the measuring transducer under study by a computing unit of signals reflecting its amplitude-frequency and phase-frequency characteristics, then comparing these characteristics with a set of normalized amplitude-frequency and phase-frequency characteristics sequentially coming from the block memory, and allocation using the blocks of selection of signals of those normalized amplitude-frequency and phase-frequency characteristics which have the smallest deviation from the amplitude-frequency and phase-frequency characteristics of the investigated measuring transducer. If the permissible deviations of the amplitude-frequency and phase-frequency characteristics of the studied measuring transducer, which are stored in the memory unit, do not exceed normalized values, then these characteristics in the form of signals are transmitted to the registration unit through the second comparator,

However, the known device also does not allow to determine the dynamic characteristics of the thermal converter, if its transient is required to be described by the sum of more than two exponential components to increase the accuracy of determining the dynamic characteristics.

The technical result to which the claimed invention is directed is to increase the accuracy of determining the dynamic characteristics of a thermal sensor by determining the parameters of three or more exponential components, which increase the accuracy of the description of the transient process.

, определяющим искомые динамические характеристики термодатчика согласно формулеThis technical result is achieved in that in a device for determining the dynamic characteristics of temperature sensors containing a series-connected unit for forming a step-like effect of temperature on a temperature sensor, a temperature sensor and a measuring transducer, it is new that the device further comprises a series-connected subtracting unit, a signal conversion unit from a temperature sensor to a damped pulse signal and a spectrum analyzer, while the output of the measuring transducer is connected to the first input of the subtracting unit, the second input of which is connected to an adjustable source of a constant level signal, the signal output of the unit for forming a step-wise influence of temperature on the temperature sensor is connected to the second input of the signal conversion unit from the temperature sensor to a damped pulse signal, and the output of the device is the output of the spectrum analyzer with a signal in the form amplitude spectrum $$\left|S\left(j\omega \right)\right|$$

determining the desired dynamic characteristics of the temperature sensor according to the formula

,

,

- амплитудный спектр сформированного сигнала;Where $$\left|S\left(j\omega \right)\right|$$

- amplitude spectrum of the generated signal;

n is the required number of exponential components in the transient process (the order of the transient process of the temperature sensor);

τ is the time of the transition process, starting from the moment the temperature sensor is placed in an environment with a lower temperature, s;

U _n - the value of the signal from the temperature sensor at the time of placement of the temperature sensor in an environment with a lower temperature;

U _to - the final value of the signal from the temperature sensor;

C _i - parameter (weight coefficient) in the i-th exponential component of the transition process;

T _i - parameter (time constant) in the i-th exponential component of the transition process, c;

ω is the angular velocity (frequency), c ^-1 .

The invention is illustrated in FIG. 1-3.

FIG. 1 is a block diagram of a device where:

1 - block forming a stepwise effect of temperature on the temperature sensor with temperature and signal outputs;

2 - temperature sensor;

3 - measuring transducer;

4 - subtraction unit with two inputs and one output;

5 - a block for converting a signal from a temperature sensor into a damped pulse signal;

6 - spectrum analyzer;

7 - adjustable source of constant level signal.

FIG. 2 - diagrams of the operation of the device, where:

FIG. 2, a - signal from the temperature output of the device;

FIG. 2, b - signal from the output of the temperature sensor 2;

FIG. 2, c - signal from the output of the measuring transducer 3;

FIG. 2, g - signal from the output of the subtracting block 4;

FIG. 2, d - the signal from the output of block 5 converting the signal from the temperature sensor into a damped pulse signal;

FIG. 2, e - signal from the output of the spectrum analyzer 6.

FIG. 3 is an example of a relay-based circuit that implements the formation of a signal from a temperature sensor into a damped pulse signal, where:

FIG. 3a - position of relay contacts at τ <0;

FIG. 3, b - the position of the relay contacts at τ≥0.

The device comprises a series-connected unit 1 for forming a step-wise influence of temperature on a temperature sensor with temperature and signal outputs, a temperature sensor 2, a measuring transducer 3, a subtracting unit 4 with two inputs and one output; block 5 converting the signal from the temperature sensor into a damped pulse signal with two inputs and one output and spectrum analyzer 6, while the second input of the subtracting block 4 is connected to an adjustable source 7 of a constant level signal, and the signal output of block 1 is connected to the second input of the signal converting block 5 from a temperature sensor to a damped pulse signal.

The device operates as follows.

Until the formation of a step-wise influence of temperature on the temperature sensor 2, the input of the spectrum analyzer 6 is disconnected from the output of the signal converting unit 5 and at the same time, the signal s (τ) of the zero level is input to the spectrum analyzer s (τ) = 0 for τ <0 (Fig. 2e). At the time instant τ = 0 of the formation of a step-by-step influence of temperature t (τ) on the temperature sensor 2 from the initial level t _n to a lower level t _to (Fig. 2, a), on a signal from the signal output of block 1, block 5 connects the output of the subtracting block 4 to the input spectrum analyzer 6. The spectrum analyzer 6 analyzes the signal s (τ), which is a damped pulse signal (Fig. 2, e) of the form

сигнала s(τ), характеризующий совокупность амплитуд гармонических составляющих, образующих сигнал s(τ), в зависимости от частоты ωThe result of the analysis is the amplitude spectrum $$\left|S\left(j\omega \right)\right|$$

signal s (τ), which characterizes the set of amplitudes of the harmonic components that form the signal s (τ), depending on the frequency ω

The signal s (τ) is generated as follows.

As a result of the stepwise influence of temperature t (τ) on the temperature sensor 2, its output signal y (τ), which is a transient response of the temperature sensor, varies in time from the level y _n to the level y _k (Fig. 2, b) according to the law

.

.

,The measuring transducer 3 converts the output signal y (τ) of the temperature sensor 2 into a proportional signal y (τ), a unified electrical signal U (τ), varying from the level U _n to the level U _к (Fig. 2, c), of the form

,

and through its output this signal is supplied to the first input of the subtracting unit 4. A signal with a pre-set level U _k from an adjustable source 7 of signals is supplied to the second input of the unit 4. At the output of the subtracting block 4, a signal U _s (τ) is created (Fig. 2d), equal to

Then, using block 5, a signal s (τ) is formed from the signal U _s (τ) satisfying expression (1).

The device can be created from known and existing in the art blocks.

If the temperature sensor 2 being tested is a temperature sensor for gas or air flows, then a wind tunnel, described in the book by A.N. Petunin, can be used as a block 1 for forming a stepwise effect of temperature. Measurement of gas flow parameters: instruments for measuring pressure, temperature and speed. - M.: Mechanical Engineering, 1974 - [3, p. 211, fig. 3.32] or the UV-010 installation, presented in OST 1 00418-81 “Method and means for determining the dynamic characteristics of gas flow temperature sensors” - [4, Appendix 1]. These installations realize the stepwise effect of temperature on the temperature sensor from the initial level t _n to the final level t _k , and t _n > t _k . In these installations, the tested temperature sensors are moved to the working parts of the wind tunnels by means of pneumatic cylinders, which are controlled by electro-pneumatic valves via buttons (single-pole switches). These buttons are designed to supply voltage to the electromagnetics electromagnetics electromagnets. When using buttons in the form of bipolar switches, the second pole can be used to simultaneously supply a signal to block 5, i.e. perform the function of the signal output from block 1.

The measuring transducer 3 is selected from among the unified transducers depending on the type of the tested temperature sensor and the required type of output signal U (τ). Examples of such converters are the universal normalizing converter Aries NPT1 and the normalizing signal converter NPSI-TP thermocouples with current analog output from the catalogs www.souz-pribor.ru - [5].

The subtracting unit 4 can be performed on the basis of well-known circuits or control devices of automation, which are described in detail in the book by A.Yu. Yalyshev and O. Razorenov Multifunctional analog control devices for automation. - M.: Mechanical Engineering, 1981 - [6, p. 158]. In FIG. 3 subtracting unit 4 is implemented according to the differential (oncoming) circuit of the inclusion of two voltage sources. In this case, the voltage at the output of block 4 is determined by the expression

U _s (τ) = U (τ) -U _to .

Block 5 converting the signal from the temperature sensor into a damped pulse signal can be implemented on the basis of an electromagnetic relay (Fig. 3). Until the formation of a stepwise effect of temperature on the temperature sensor, the contacts K1 and K2 of the electromagnetic relay K are closed, and the contacts K1 and K3 are open (Fig. 3, a). In this case, the input of the spectrum analyzer 6 is short-circuited, which provides a zero input signal s (τ) at its input. At time moment τ = 0, when a step-like effect of temperature on the temperature sensor is formed, relay K is activated by a signal from the signal output of unit 1. In this case, contacts K1 and K3 are closed, and contacts K1 and K2 are opened and a signal starts to enter the spectrum analyzer 6 U _s (τ) from the output of the subtracting block 4 (Fig. 3, b). When used as a block 1 wind tunnels described in [3, p. 211, fig. 3.32; 4, Appendix 1], the voltage across the relay coil K of block 5 (Fig. 3) at time τ = 0 can be supplied through an additional pole of the switch, which supplies voltage to the electromagnetically solenoid valves.

The spectrum analyzer 6 refers to laboratory electro-radio measuring equipment and is selected according to the expected frequency range. Representatives of such analyzers are devices of the AKS, AKIP, GSP, NS, LSA, etc. series in the catalogs of Soyuz-pribor LLC [5] and PRIST CJSC www.prist.ru - [7].

An adjustable source 7 of a constant level can also be performed on the basis of laboratory electro-radio-measuring equipment. Representatives of such regulated power sources are devices of the ATH, PS, PP, GP series and others in the catalogs of Soyuz-pribor LLC [5] and PriST CJSC [7].

The rationale for achieving a technical result.

As follows from the book Yarysheva N.A. Theoretical foundations of measuring non-stationary temperatures. - L .: Energy, 1967 - [8, p. 136], the transition process of cooling temperature sensors in a medium with a constant temperature in the general case can be described by the sum of an infinite number of exponential components of the form

where U (τ) is the converted output signal from the temperature sensor;

.

.

In practice, the number n of exponential components in (3) is limited, depending on the requirements for the accuracy of the description of the transient process. The lowest description accuracy corresponds to n = 1, i.e. description by one exponent. More precisely, the transient can be described by the sum of two exponential components. Each subsequent increase in the number of exponential components in (3) makes it possible to increase the accuracy of the description of the transitional temperature sensor, providing an increase in the accuracy of determining its dynamic characteristics.

In the book, Granovsky V.A. Dynamic measurements: Fundamentals of metrological support. - L.: Power Publishing House. Leningra. Department, 1984 - [9, Fig. 3.12] presents a diagram of the response of a film thermal receiver and its 1st, 2nd, and 3rd orders of magnitude to a step test signal and estimates the accuracy of the approximation. From [9, tab. 3.7] it is seen that each subsequent increase in the order of n of the model increases the accuracy of the description of the transient process of the thermal receiver. So, for example, the maximum modulus of the difference between the responses of the models and the thermal receiver for n = 1 is 19 srvc. units, for n = 2-3.4 srvc. units, and for n = 3-3 conv. units

As is known, if a signal is given as a non-periodic function of time that satisfies the Dirichlet conditions and is absolutely integrable within infinite time limits, then this function has its own spectrum S (jω), which is sometimes called the complex spectral density, spectral density, or spectral characteristic of the signal.

, связанного с параметрами C_i и T_i затухающего переходного процесса термодатчика, сигнал вида (3) предлагается в заявляемом устройстве преобразовать. Для этого, до размещения термодатчика в среде с меньшей температурой устанавливают конечное значение сигнала U_к с термодатчика, соответствующее окончанию переходного процесса, и на это значение настраивают уровень сигнала с источника 7 сигнала постоянного уровня. Затем измеряют значение сигнала U_н с термодатчика в момент его размещения в среде с меньшей температурой и формируют сигнал s(τ)=U(τ)-U_к с помощью блоков 4, 5 и 7, являющийся разностью между выходным U(τ) и конечным U_к значениями сигнала с термодатчика, начиная с момента размещения термодатчика в среде с меньшей температурой до окончания переходного процесса. С помощью анализатора 6 спектра определяют амплитудный спектр $$\left|S\left(j\omega \right)\right|$$

сформированного сигнала, который имеет аналитический вид (2).A signal of the form (3) does not satisfy the aforementioned conditions, since at τ <0 the converted output signal of the temperature sensor is U (τ) = U _н , and at τ → + ∞ the converted output signal is U (τ) → U _к . For the possibility of obtaining the amplitude spectrum $$\left|S\left(j\omega \right)\right|$$

associated with the parameters C _i and T _{i of the} damping transient of the temperature sensor, a signal of the form (3) is proposed to be converted in the inventive device. For this, before placing the temperature sensor in an environment with a lower temperature, the final value of the signal U _k from the temperature sensor is set, which corresponds to the end of the transient, and the signal level from the source 7 of the constant level signal is adjusted to this value. Then measure the value of the signal U _n from the temperature sensor at the time of its placement in a medium with a lower temperature and form the signal s (τ) = U (τ) -U _k using blocks 4, 5 and 7, which is the difference between the output U (τ) and final U _{to the} values of the signal from the temperature sensor, starting from the moment the temperature sensor is placed in an environment with a lower temperature until the end of the transient process. Using the spectrum analyzer 6, the amplitude spectrum is determined $$\left|S\left(j\omega \right)\right|$$

the generated signal, which has an analytical form (2).

вычисляют параметры C_i и T_i затухающего переходного процесса термодатчика требуемого порядка n согласно формуле (2), используя различные известные математические методы.According to the amplitude spectrum determined from the generated signal $$\left|S\left(j\omega \right)\right|$$

calculate the parameters C _i and T _{i of the} damping transient of the temperature sensor of the required order n according to formula (2) using various known mathematical methods.

The final value U _{k of the} signal from the temperature sensor can be pre-set either by calculation or by directly measuring the signal from the temperature sensor, previously placed in a medium with a lower temperature.

To calculate the parameters of the decaying transient process of the temperature sensor according to formula (2), it is advisable to use regression analysis methods that ensure that the analytical expressions of the corresponding amplitude spectra are closer to their experimental spectra with the smallest standard error.

The parameters of the decaying transient of the temperature sensor can also be calculated by directly solving the system of equations composed of the corresponding analytical expressions of the amplitude spectrum. For example, for n = 3, it is necessary to solve the system with respect to the six desired parameters C ₁ , C ₂ , C ₃ , T ₁ , T ₂ and T ₃ , consisting of six equations of the form

,

,

where ω _k are the frequencies selected in the frequency range of a certain amplitude spectrum (k = 1, 2, ..., 6);

- значения определенного амплитудного спектра на частотах ω_k. $$\left|S\left(j{\omega }_k\right)\right|$$

- values of a certain amplitude spectrum at frequencies ω _k .

The proof of the connection of a signal of the form (1) with expression (2) is as follows.

As is known, the amplitude spectrum of some non-periodic signal f (τ) satisfying the Dirichlet conditions has the form

For the signal s (τ) formed in the proposed method, expression (4) takes the form

.

.

, поскольку современные анализаторы спектра. имеют разнообразные встроенные возможности обработки спектрограмм, а также в них предусмотрено управление от персональных компьютеров и по сети Ethernet.The proposed device will allow for a simple technical solution to obtain the desired dynamic characteristics of temperature sensors with high accuracy, by determining the parameters of three or more exponential components. The spectrum analyzer included in the device will also simplify the subsequent procedure for processing the amplitude spectrum $$\left|S\left(j\omega \right)\right|$$

because modern spectrum analyzers. They have various built-in processing capabilities for spectrograms, and they also provide control from personal computers and via Ethernet.

Claims (1)

A device for determining the dynamic characteristics of temperature sensors, comprising a series-connected unit for the formation of a step-like effect of temperature on the temperature sensor and a measuring transducer, characterized in that it further comprises a series-connected subtracting unit, a unit for converting a signal from a temperature sensor into a damped pulse signal and a spectrum analyzer, while the measurement output the converter is connected to the first input of the subtracting unit, the second input of which is connected to the regulation to a constant-level signal source, the second output of the step-by-step temperature forming unit for the temperature sensor is connected to the second input of the signal conversion unit from the temperature sensor to a damped pulse signal, and the output of the device is the output of the spectrum analyzer with a signal in the form of the amplitude spectrum | S (jω) | the desired dynamic characteristics of the temperature sensor according to the formula

,
where | S (jω) | - amplitude spectrum of the generated signal;
n is the required number of exponential components in the transient process (the order of the transient process of the temperature sensor);
τ is the time of the transition process, starting from the moment the temperature sensor is placed in an environment with a lower temperature, s;
U _n - the value of the signal from the temperature sensor at the time of placement of the temperature sensor in an environment with a lower temperature;
U _to - the final value of the signal from the temperature sensor;
C _i - parameter (weight coefficient) in the i-th exponential component of the transition process;
T _i - parameter (time constant) in the i-th exponential component of the transition process, s;
ω is the angular velocity (frequency), s ^-1 .

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