RU2495390C1 - Measuring temperature of average temperature of non-homogeneous medium, and device for its implementation - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: according to the proposed method, there measured is oscillator frequency depending on parameters of thermoresistors located uniformly in the volume of the investigated field and connected to external capacitors and of phasing RC circuit, forming together with an amplifier an oscillator connected through a frequency-code converter and a microcontroller, the programme of which is provided with a calibration characteristic of frequency dependence on the controlled temperature. The invention also presents possibility of correcting instrument measurement error during calibration after installation of thermoresistors in controlled medium and setting of the value of frequency corresponding to minimum and maximum average medium temperature, and when they are achieved, and additional indication mode is activated. After processing with the controller the result is transmitted to a control channel or to a temperature indicator.

EFFECT: improving measurement accuracy of medium temperature.

3 cl, 3 dwg

Description

The invention relates to measuring equipment, and in particular to methods and means of measuring the average temperature of sections of the medium with an inhomogeneous temperature field, and is intended for use in environmental monitoring systems and process control.

A known method of measuring the average value of a parameter, in particular temperature, an inhomogeneous medium (RF patent No. 2115098, publ. 07/10/1998, G01K 3/02, G01D 1/02), comprising converting the current values of the parameters into a proportional voltage using sensors. In the proposed method, the deployment voltage is formed, compared with the current output voltage of each of the sensors, at the moment of the equality of the compared voltages on one of the sensors, the current value of the deployment voltage is estimated and summed to the cumulative sum of such voltages, and after the deployment voltage reaches its highest value, it is divided the accumulated amount by the number of sensors in the controlled group and the obtained quotient are taken as the measured average value of the parameter. The transmission of signals about the equality of the current values of the deployment voltage and the voltages at the outputs of the sensors is transmitted by a code, in particular paraphase, which makes it possible to detect the overlap of signals during transmission, and in case of detection of their overlap, the doubled current value of the deployment voltage is added to the accumulated sum of voltages. In the process of transmission, the number of transmitted signals is calculated that occurs when the deployment voltage is equal to the voltage at the outputs of the sensors, and if this number turns out to be less than the actual number of monitored sensors by a predetermined value, then re-measurement is performed at a specified lower slew rate of the deployment voltage.

A device is known for measuring the average value of a parameter, in particular temperature, an inhomogeneous medium (RF patent No. 2107269, publ. March 20, 1998, G01K 3/02) containing a distributed thermal converter made in the form of a bundle of n-wire thermal converters, the first terminals of which are connected respectively, with the first terminals of n current generators, the second terminals of which are connected respectively to the first terminals of n resistors, a switch whose output is connected to the register, and the inputs are connected to the outputs (n-1) of the decoupling amplifiers, the first inputs s which are respectively connected to the second output resistors except for the last resistor, the second terminal of which is connected to the second input of the (n-1) -th amplifier and decoupling the second output n-th wire thermocouple. The device additionally contains (n-1) additional resistors, each of which is connected between the second terminals of the corresponding wire thermocouples and resistors, and the second inputs of the decoupling amplifiers with the exception of the last amplifier are connected respectively to the second terminals of the wire converters with the exception of the first and last, with each wire thermocouple consists of direct and return wires, and the length of each k-th wire thermal converter is greater than the length of the (k-1) -th wire thermocouple of the magnitude L, equal to the length averaging portion. A group of comparators, a group of formers, an OR element, a setter, a generator, a memory element, an And element, the first and second counters, a digital-to-analog converter, a group of readout amplifiers, a computational unit, first and second indicators and a control unit, the input group of which is connected to the group, are introduced into the device the outputs of the first counter and the groups of inputs of the DAC and the group of read amplifiers, the first and second inputs and the output of the comparators of the group are connected to the output of the corresponding sensor, the output of the DAC and the input of the corresponding driver, respectively, the input The s of the OR element are connected to the outputs of the corresponding shapers, and its output is connected to the summing input of the second counter, the input of the group of read amplifiers and the first input of the computing unit, the first input of the memory element is connected to the output of the master and zeroing inputs of the first and second counters, its second input is connected to the output of the control unit and the second input of the computing unit, the output is connected to the first input of the element And, the outputs of the generator and the element And are connected to the second output of the element and the summing input of the first etchika respectively, a group of inputs and outputs of the computing unit group and the second group of inputs connected to a group indicator group of sense amplifiers outputs, the group of inputs of the first indicator and the second group of counter outputs, respectively.

The disadvantages of analogues are the influence of many connecting wires from sensors to comparators on an informative parameter - voltage, a large number of conversions and the complexity of the circuit, which reduces reliability, as well as the need for repeated measurements in some cases.

The closest in technical essence is an automated system for measuring temperature fields using quasi-distributed piezoresonance sensors (http://www.qsens.ru/developers/81-quazi.html Last updated 02/02/2010). An automated system is a chain of many (tens and hundreds) of parallel-connected point (discrete) piezoresonant temperature sensors located at the control points of the measured temperature field and forming the master circuit of the sinusoidal oscillation generator, which makes it possible to use a signal processing unit for connecting to it via a two-wire line , analog I / O unit, digital signal processing unit, control unit, storage device, control panel and indie cator.

The method is implemented by a device for measuring and processing the frequency of the generator, depending on the parameters of quasi-distributed piezoresonance sensors placed at the control points of the measured temperature field.

The main significant drawback of an automated system for measuring temperature fields using quasidistributed piezoresonance sensors is the use of special piezoelectric elements that require protection from aggressive environments, and their high cost compared to thermistors.

The task of the claimed invention is to simplify the continuous measurement of the average temperature of a medium with a non-uniform temperature field and to develop a device for its implementation using the same standard thermistors, which will provide high reliability.

The problem is solved by implementing a method of measuring the average temperature of a medium with an inhomogeneous temperature field by measuring the frequency of the generator, depending on the parameters of the thermistors, according to which the thermistors are evenly distributed over the studied field and connected to the external capacitors of the phasing RC circuit, which together with the amplifier forms a generator connected through a frequency-code converter and a microcontroller, the program of which is provided with a calibration characteristic awns frequency controlled by a temperature controller after the processing result is supplied to the channel or to regulate the temperature indicator.

In addition, the microcontroller program is provided with the ability to correct the instrumental measurement error during calibration after installing the thermistors in a controlled environment.

In addition, the program of the microcontroller is equipped with a frequency value corresponding to the minimum and maximum average temperature of the medium, upon reaching which include an additional display mode.

The problem is also solved by a device for measuring the average temperature of a medium with a non-uniform temperature field containing thermistors, a generator connected via a frequency-code converter and a microcontroller with an indicator, in which according to the invention, the thermistors make up RC elements of the phasing chain (FC) with external capacitors, forming a generator together with an amplifier.

In addition, the essence of the technical solutions is illustrated by drawings, where:

- figure 1 shows the Converter chain structure;

- figure 2 is a schematic diagram of a phasing chain;

- figure 3 is a measurement circuit using thermistors as elements of the phasing chain of an RC generator.

Essence: the method is implemented using standard thermistors, at least three, arranged uniformly over the controlled volume and forming together with external capacitors a phasing RC - a chain of a harmonic oscillation generator, the frequency of which depends on the average temperature of the medium.

Known traditional research methods do not allow obtaining analytical expressions that relate the average temperature of the medium to the generation frequency, which depends on the simultaneous individual change of the parameters of several thermistors, and, therefore, solve the actual problem.

Using the method of transformation functions (FP) allowed to eliminate this gap (see Gulin A.I. Diagnostics of measuring transducers and communication devices with an inhomogeneous chain structure // Control. Diagnostics. 20.10. No. 11. P.69-72).

FP K _{n of the} converter of the chain structure (Fig. 1) (formally, the reciprocal of the traditional transfer coefficient), which is the ratio of the input active quantity U ₀ to the output B _n (voltage U _n or current I _n ) is described by the expression for an even number of arms n

$$K_n=\mathrm{one}+{\displaystyle \sum _{\begin{array}{l}i=\mathrm{one}\\ k=i+\mathrm{one}\end{array}}^{\begin{array}{l}n\\ n-\mathrm{one}\end{array}}{Z}_i{Y}_k+}{\displaystyle \sum _{\begin{array}{l}i=\mathrm{one}\\ k=i+\mathrm{one}\end{array}}^{\begin{array}{l}n-2\\ n-3\end{array}}{\displaystyle \sum _{\begin{array}{l}p=k+\mathrm{one}\\ q=p+\mathrm{one}\end{array}}^{\begin{array}{l}n\\ n-\mathrm{one}\end{array}}{Z}_i{Y}_k{Z}_p{Y}_q+...}},(\mathrm{one})$$

where i = 2b-1;

b = 1,2,3, ..., 0,5n,

and for chain structures (CS) with an odd number of shoulders n

$$K_n={\displaystyle \sum _{i=\mathrm{one}}^n{Z}_i+}{\displaystyle \sum _{\begin{array}{l}i=\mathrm{one}\\ k=i+\mathrm{one}\end{array}}^{\begin{array}{l}n-\mathrm{one}\\ n-2\end{array}}{\displaystyle \sum _{p=k+\mathrm{one}}^n{Z}_i{Y}_k{Z}_p+...}},(2)$$

where b = 1,2,3, ..., 0,5 (n + 1) for a CA with an odd number of shoulders n.

Relations (1) and (2) lead to a recurrence formula for calculating the phase transition

$$K_n=T_n{K}_{n-\mathrm{one}}+K_{n-2},(3)$$

where T _{i is the} immitance of the ith arm (resistance Z for odd i and conductivity Y for even i).

The initial conditions of the calculation algorithm K _n are the values K ₀ = 1 for n = 0 and K ₁ = T ₁ for n = 1.

The recommended circuit diagram of an RC phasing chain (FC) is shown in FIG. 2. Therefore, the required minimum number of thermistors to create a FC should be at least three. The article (see Gulin A.I. Design of multi-link RC generators // Izv. Universities "Instrument Making", 2012. Vol. 15. No. 1 (41). S.14-118) presents all kinds of FC schemes that can be used to build various circuits of measuring generators. For large areas of a controlled environment, the number of thermistors is increased to the required number, spreading uniformly throughout the space.

The expression of the AF of the six-armed FC according to (1) will be

$$\begin{array}{l}{K}_6=\mathrm{one}+Z_{\mathrm{one}}{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="00000021.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2+Z_{\mathrm{one}}{Y}_{\mathrm{four}}+Z_{\mathrm{one}}{Y}_6+Z_3{Y}_{\mathrm{four}}+Z_3{Y}_6+Z_5{Y}_6+Z_{\mathrm{one}}{Y}_2{Y}_3{Y}_{\mathrm{four}}\\ +Z_{\mathrm{one}}{Y}_2^{}{Z}_3{Y}_6+Z_{\mathrm{one}}{Y}_2{Z}_5{Y}_6+Z_{\mathrm{one}}{Y}_{\mathrm{four}}{Z}_5{Y}_6+Z_3{Y}_{\mathrm{four}}{Z}_5{Y}_6+Z_{\mathrm{one}}{Y}_2{Z}_3{Y}_{\mathrm{four}}{Z}_5{Y}_6.(\mathrm{four})\end{array}$$

For FC (Figure 2), when Z ₁ = Z ₃ = Z ₅ = 1 / jωС, and Y ₂ = Y ₄ = Y ₆ = 1 / R, the FP will be equal to $$K_6=\mathrm{one}+\frac{6}{j\omega CR}-\frac{5}{{\omega }^2{C}^2{R}^2}-\frac{\mathrm{one}}{j{\omega }^3{C}^3{R}^3}(5)$$

In the components of the real and imaginary parts, the phase transition has the form

K ₆ = ReK ₆ + ImK ₆ ,

The condition for oscillations when using FC is

$$K_{\mathrm{BUT}P}\cdot {\mathrm{TO}}_{F\mathrm{Ts}}\le \mathrm{one,}(6)$$

where K _AP - FP active converter (amplifier);

K _FC - FP phasing chain.

Because The amplifier phase is real, in order to fulfill condition (6) it is necessary that the phase transition center K K _center at the self-excitation frequency is also real. In this case, both phase transitions can simultaneously have either positive or negative values, i.e. FC, depending on the type of active converter, must carry out a phase shift by an even or odd number πi radians, where i = 1, 2, 3 ... is a natural series of numbers.

Consider the question of determining the frequency of quasiresonance in a six-arm FC (Figure 2), composed of RC elements and performing a phase rotation of 180 °, which is most often used when constructing generators on single-stage amplifiers. The frequency of quasi-resonance is determined from the imaginary part of the phase transition phasing quadripole when it vanishes, i.e.

$$\mathrm{Im}\cdot K_{fc}=0(7)$$

Equating the imaginary part of the phase transition (quasi-resonance condition) of expression (5) to zero, we obtain the formula for the desired frequency ω _{0 of the} six-arm FC

; $$\mathrm{Im}{K}_6=\frac{6}{j\omega CR}-\frac{\mathrm{one}}{j{\omega }^3{C}^3{R}^3}$$

;

; $$\frac{6}{j\omega CR}-\frac{\mathrm{one}}{j{\omega }^3{C}^3{R}^3}=0$$

;

; $$\frac{6}{j\omega CR}-\frac{\mathrm{one}}{j{\omega }^3{C}^3{R}^3}$$

;

.where from $${\omega }_0=\frac{\mathrm{one}}{RC\sqrt{6}}$$

.

We determine the real part of the phase transition ReK ₆ FC at the frequency of quasi-resonance ω ₀ from expression (5)

, $$\mathrm{Re}{K}_6=\mathrm{one}-\frac{5}{{\omega }^2{C}^2{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="00000021.png"\; state="\{\{state\}\}">R</figure-callout>}}^2}$$

,

and substituting the value of the frequency of quasi-resonance from (8), we define

. $$\mathrm{Re}{K}_6=-\mathrm{29th}$$

.

FC attenuates the signal level by 29 times, and a minus sign confirms a phase rotation of 180 °. Therefore, K _AP - AF of the active transducer (gain) should exceed more than 29 times.

Calculations for calculating the frequencies of quasi-resonances for an arbitrary number of temperature sensors n / 2 are reduced, as it turned out, to determining the coefficient k _{n of the} expression

$${\omega }_0=\frac{\mathrm{one}}{k_{n}CR}$$

As a result of the analytical analysis, the formula was first obtained, which determines the coefficient k _n for the FC from any number of temperature sensors from equations of the form

$${\displaystyle \sum _{i=0.1...}^P{(-\mathrm{one})}^i{k}_n^{2i+\mathrm{one}}{C}_{0.5n+\mathrm{one}+2\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="00000021.png"\; state="\{\{state\}\}">i</figure-callout>}}^{2+\mathrm{four}i}=0(9)}$$

where p = 0.25n-1 - for even 0.5n;

p = 0.25 (n + 2) -1 - for odd 0.5n.

For example, for ten-arm (five-link) FC equation (9) has the form 15k-28k ³ + k ⁵ = 0, the solution of which gives the following values of k:

k _1,2 = ± 23/32; k _3.4 = ± 167/32; k ₅ = 0.

), так как использование других значений, удовлетворяющих (9), приведет к сдвигу фаз на 2π радиан и более.Of all the real positive roots of equation (9), it is necessary to use the smallest value k = 23/32 (for six-arm-three-link FC it is $$\sqrt{6}$$

), since the use of other values satisfying (9) will lead to a phase shift of 2π radians or more.

To calculate more complex FCs, you can use the program (see Gulin A.I., Sukhinets Zh.A. et al. Calculation of the frequency of quasi-resonance and transmission coefficient of multi-link RC structures // Certificate of official registration of a computer program No. 2003611147 / 05.16.2003 Rospatent. Moscow. 2003).

до $$K_n=-\mathrm{11,6}$$

, т.е. $$\underset{n\to \infty }{\lim }\left|K_n\right|=\mathrm{11,6}$$

.It should be noted that the phase transition K _n FC at the frequencies of quasi-resonance with increasing number of arms n from six to infinity decreases and tends from $$K_6=-\mathrm{29th}$$

before $$K_n=-11.6$$

, i.e. $$\underset{n\to \infty }{\lim }\left|K_n\right|=11.6$$

.

A device for measuring the average temperature of an inhomogeneous medium at object 1 contains thermistors 2 that make up elements of a phasing chain 3 with external capacitors to form a master oscillator 5 connected with an amplifier 4, connected via a frequency-code converter 6 and a microcontroller 7 with a digital indicator 8.

The microcontroller program is provided with a calibration characteristic of the dependence of the frequency on the average temperature of the medium,

In addition, the microcontroller program is provided with the ability to correct the instrumental measurement error during calibration after installing the thermistors in a controlled environment.

In addition, the microcontroller program is equipped with a frequency value corresponding to the minimum and maximum average temperature of the medium, upon reaching which they include an additional display mode that attracts the attention of the operator.

Measurement of the average temperature of an inhomogeneous medium at object 1 is as follows. The same type of thermistors (temperature sensors) 2 are evenly placed in a controlled environment, connected to external capacitors to form a phasing chain 3, and together with an amplifier 4, a master oscillator 5, which is connected through a frequency-code converter 6 and microcontroller 7 with a digital indicator 8. With uneven temperature fluctuations in the controlled environment at the object, the resistance values of the thermistors forming the phasing chain 3 of generator 5 change. In accordance with the values of these resistances poured frequency generator 5, which is converted to the frequency converter 6 code in the code, and the result is processed by the microcontroller 7 to temperature units and displayed on the display 8 in these units. The microcontroller programmatically provides for setting the values of the minimum and maximum average temperature of the medium, upon reaching which they include an additional display mode that attracts the attention of the operator, and the calibration characteristics of the dependence of the frequency on the average temperature of the medium.

So, the claimed invention allows you to continuously measure the average temperature of a heterogeneous medium using a two-wire communication line and the same type of standard thermistors (temperature sensors), which ensures high reliability of the method.

Claims (4)

1. A method of measuring the average temperature of an inhomogeneous medium by measuring the frequency of the generator, depending on the parameters of the thermistors, characterized in that the thermistors are evenly distributed over the studied field and connected to external capacitors of the phasing RC circuit, which together with the amplifier forms a generator connected through a frequency converter code and microcontroller, the program of which is equipped with a calibration characteristic of the dependence of the frequency on the controlled temperature, after processing by the controller Performan fed into the channel or adjusting the temperature display. 2. The method according to claim 1, characterized in that the microcontroller program is provided with the ability to correct the instrumental measurement error during calibration after installing the thermistors in a controlled environment. 3. The method according to claim 1, characterized in that the microcontroller program is provided with a frequency value setting corresponding to the minimum and maximum average temperature of the medium, upon reaching which include an additional display mode. 4. A device for measuring the average temperature of an inhomogeneous medium containing thermistors, a generator connected via a frequency-code converter and a microcontroller with an indicator, characterized in that the thermistors make up RC elements of the phasing chain with external capacitors, which form a generator together with the amplifier.

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