RU2207529C1 - Digital temperature meter - Google Patents

Abstract

FIELD: development of digital temperature meters operating with use of thermal converters forming frequency output signal. SUBSTANCE: digital temperature meter includes thermal converter forming frequency output signal; first and second frequency generators; reversing and adding counters; three AND-gates; flip-flop; indicator; frequency/code and code/frequency converters. Temperature meter includes in addition register whose code input is connected with outlet of reversing counter. Direct dynamic writing inlet of register is connected with outlet of flip-flop. Outlet of register is connected with code inlet of code/frequency converter. EFFECT: enhanced quick action of digital temperature meter. 3 dwg

Description

Изобретение может быть использовано при построении цифровых термометров, работающих с термопреобразователями, имеющими частотный выходной сигнал, например, пьезокварцевыми термопреобразователями.The invention relates to temperature measurements and is intended to work with thermal converters with a frequency output signal, in which the output frequency F is associated with the temperature t ^{o the} dependence

The invention can be used in the construction of digital thermometers working with thermal converters having a frequency output signal, for example, piezoelectric quartz thermal converters.

 A known digital thermometer [1], comprising a temperature converter with a frequency output, a mixing frequency generator, a mixer, a counter, two switching elements, a matching circuit, a control circuit, an And circuit, a result counter, a sign trigger, a reversible indication system. In this device, the thermal-frequency characteristic of a real thermal converter is linearized using a piecewise linear approximation.

 The disadvantages of the digital thermometer [1] are low accuracy due to the presence of a methodological error in the approximation of the quadratic function and low noise immunity due to the need for consistent selection of temperature ranges in the absence of control over the state of the output information.

 Of the analogues, the closest in technical essence is a digital thermometer [2], which is chosen as a prototype. The prototype in comparison with the analogue has higher accuracy due to the lack of methodological error and has better noise immunity due to the implementation of the averaging operator.

 The prototype includes: a thermal converter with a frequency output, first and second frequency generators, reversible and totalizing counters, three AND elements, a trigger, an indication unit, frequency converters in code and a code in frequency, the thermal converter output being connected to the trigger installation input, resetting the input which is connected to the transfer output of the totalizing counter connected by the counting input to the output of the first element And, the first input of which is connected to the output of the first frequency generator, and the second to the trigger output and with the second inputs of the second and third elements And, and the first inputs of these elements And are connected respectively the second - with the output of the second frequency generator and with the reference frequency input of the code to frequency converter, and the third - with the output of the code to frequency converter and with the subtracting input of the reversible counter, summing up the input of this counter is connected to the output of the second element And, and the output of the third element And is connected to the input of the frequency converter into a code, the output of which is connected to the input of the display unit, in addition, in the prototype The single input of the code-to-frequency converter is connected to the output of the reverse counter.

где F(t^o) - выходная частота термопреобразователя;
t^o - температура;
а - постоянный коэффициент.The prototype [2] operates in a continuous mode and provides linearization of the characteristics of thermal converters with the dependence

where F (t ^o ) is the output frequency of the thermal converter;
t ^o is the temperature;
a is a constant coefficient.

Pulse signal from the output of the thermal converter due to the quadratic functional characteristic of the thermometer
N = F (t ^o ) ² F ₂ k ² Θ / F ₁ ² ,
under the condition
a = F ₂ k ² Θ / F ₁ ² ,
without methodological error is uniquely associated with the measured temperature
N = t ^o .

Here:
F ₁ and F ₂ - the frequency of the pulse sequences from the outputs of the first and second frequency generators;
k is the division coefficient of the counter 5;
Θ - time, much longer than the pulse repetition period from the thermal converter.

 The disadvantage of the prototype [2] is the long exit time to steady state.

 The task to which the invention is directed is the creation of a digital thermometer with accelerated testing of changes in the frequency of the output signals of the thermal converter.

 The technical result is to increase the speed of a digital thermometer.

 The solution to this problem lies in the fact that a digital thermometer, which includes: a temperature converter with a frequency output, first and second frequency generators, reversible and totalizing counters, three I elements, a trigger, an indication unit, frequency to code and code to frequency converters moreover, the output of the thermal converter is connected to the installation input of the trigger, the resetting input of which is connected to the transfer output of the totalizing counter connected by the counting input to the output of the first element And, the first input of which is connected to the course of the first frequency generator, and the second with the trigger output and with the second inputs of the second and third AND elements, the first inputs of these AND elements being connected respectively to the second with the output of the second frequency generator and with the reference frequency input of the code to frequency converter, and the third with the output of the code to frequency converter and with the subtracting input of the reverse counter, the summing input of this counter is connected to the output of the second element And, and the output of the third element And is connected to the input of the frequency converter to the code, the output of which It is connected to the input of the display unit, in addition, a register is entered, the code input of which is connected to the output of the reversible counter, the direct dynamic input of the recording is with the trigger output, and the output is with the code input of the code to frequency converter.

 The essence of the invention consists in the creation of a digital thermometer with high speed linearization of the frequency signal through the use of memory feedback when obtaining a quadratic dependence, thereby accelerating the processing of frequency changes of the output signals of the thermal converter.

 The essence of the invention is illustrated by drawings, where figure 1 shows a functional diagram of the proposed digital thermometer, figure 2 - time diagrams of the transition process, and figure 3 - time diagrams of the processes occurring in the device in steady state.

 The digital thermometer contains a temperature converter 1 with a frequency output, first and second frequency generators 2 and 3, a reversing and summing counters 4 and 5, three elements 6, 7 and 8, a trigger 9, an indication unit 10, frequency converters in code 11 and code in frequency 12, as well as register 13, and the output of the thermal converter 1 is connected to the installation input of the trigger 9, the reset input of which is connected to the transfer output of the totalizing counter 5, connected by the counting input to the output of the first element And 6, the first input of which is connected to the output of the first generator 2, and the second with the output of trigger 9 and with the second inputs of the second 7 and third 8 AND elements, the first inputs of these elements And connected respectively to the second 7 - with the output of the second frequency generator 3 and with the reference frequency input of the code converter to frequency 12 and the third 8 - with the output of the code converter to frequency 12 and with the subtracting input of the reverse counter 4, the summing input of this counter 4 is connected to the output of the second element And 7, and the output of the third element And 8 is connected to the input of the frequency converter to code 11, the output of which P connected to the input of the display unit 10, the code input of the register 13 is connected to the output of the reversible counter 4, the direct dynamic input of the recording is connected to the output of the trigger 9, and the output is connected to the code input of the code to frequency 12 converter.

Цифровой термометр работает следующим образом.The digital thermometer operates in a continuous mode and provides linearization of the characteristics of thermal converters with the dependence

Digital thermometer works as follows.

Suppose that at the initial moment of time, the counters 4, 5 and the register 13 are reset, the frequency generators 2 and 3 generate pulse sequences with frequencies F ₁ and F ₂ , the thermal converter 1 generates a frequency F (t ^o ).

The first pulse from the output of the thermal converter 1 is supplied to the installation input of the trigger 9, setting it to unity. The appearance of a single level at the output of trigger 9 initiates the recording of a zero code from counter 4 to register 13, and fixing this level ensures the passage through element 6 of pulses following with frequency F ₁ from the output of frequency generator 2 to the counter input of counter 5 and through element And 7 pulses following with a frequency of F ₂ from the output of the frequency generator 3 to the summing input of the reversing counter 4. The zero code contained in register 13 causes the absence of pulses at the output of the code to frequency 12 converter, therefore, the reverse input to the subtracting input counter 4 and the input of the frequency Converter in code 11 pulses are not received.

 At the moment when an overflow occurs in counter 5, the transfer signal will reset trigger 9, which will block the receipt of pulses from the output of the frequency generator 2 to the counting input of the counter 5 and pulses from the output of the frequency generator 3 to the summing input of the reverse counter 4. This device state will be remain until the next pulse from the output of the thermal Converter 1.

The next pulse from the output of the thermal converter 1 is supplied to the installation input of the trigger 9, setting it to unity. The appearance of a single level at the output of the trigger, as in the previous case, initiates the recording of the accumulated code from the counter 4 to register 13. A fixed single level at the output of the trigger 9 provides the passage of pulses from the output of the frequency generator 2 to the counting input of the counter 5, pulses from the output of the frequency generator 3 to the summing input of the reverse counter 4 and, in addition, the passage of pulses from the output of the code converter to frequency 12 to the input of the frequency converter to code 11 through element And 8. The code generated by the converter you are in code 11, is indicated by the display unit 10. The pulses generated by the code converter to frequency 12 under the influence of the code contained in register 13 and the pulses following with frequency F ₂ from the output of frequency generator 3 are fed to the subtracting input of the reverse counter 4.

 At the moment when an overflow occurs in counter 5, the transfer signal will reset trigger 9, which will block the arrival of pulses from the output of the frequency generator 2 to the counting input of the counter 5, pulses from the output of the frequency generator 3 to the summing input of the reverse counter 4, and also pulses with the output of the code converter to frequency 12 to the input of the frequency converter to code 11. This state of the device will remain until the next pulse from the output of thermal converter 1.

 With the arrival of the next pulse from the output of the thermocouple 1, the process repeats.

 The principle of operation of a digital thermometer is based on modulation of the reference frequency-pulse sequence by pulse-width signals with a constant duration and a period that varies depending on the input signal, which determines the response feedback time, in order to generate and automatically compensate for the device mismatch signal when receiving a linearizing quadratic dependence, which provides quick tracking of input data changes when generating the result.

The presence of negative feedback in the device provides access to the steady-state dynamic equilibrium mode, characterized by the equality of the number of pulses arriving at the summing N ₊ and subtracting N _- inputs of the reverse counter 4 during the time interval τ, i.e.

N ₊ = N _- or F ₊ = F _- , (1)
where F ₊ and F _- are the average frequencies of the pulse sequences at the summing and subtracting inputs of the counter 4, respectively.

The average value of the frequency of the pulse sequence at the summing input of the counter 4 for the period of the signal from the temperature sensor is determined as follows
F ₊ = F ₂ γ,
where γ is the relative duration of a unit level at the trigger output for the period of the temperature sensor signal.

The subtracting input of the reverse counter 4 receives a pulse sequence from the output of the code converter to the frequency 12
F _- = F ₂ N _RG / 2 ⁿ ,
where N _RG is the input code of the code converter to the frequency 12, removed from the output of the register 13,
n is the bit depth of the code to frequency 12 and register 13 converter.

In the steady state, the number of pulses arriving at the summing and subtracting inputs of the reverse counter during the time Θ of the device are equal, which allows us to obtain the following equality
F ₂ γ = F ₂ N _RG / 2 ⁿ ,
or
γ2 ⁿ = N _RG . (2)
In this case, a pulse sequence with a frequency of F 12 will be generated at the output of the code-to-frequency converter ₁₂ , modulating it with a signal taken from the output of trigger 9 will allow one to obtain a resulting pulse sequence with an average frequency value for the period of the signal from the temperature sensor
F _{o out} = F ₁₂ γ,
or taking into account the characteristics of the code-to-frequency converter 12
F o _out = γF ₂ N _RG / 2 ⁿ .

Hence, in view of (2), we have
F _{o out} = F ₂ γ ² . (3)
The width n of the code to frequency converter 12, the register 13 and the reverse counter 4 determines the accuracy of the transformations. Thus, the value of the reference frequency F ₂ is set based on the bit depths of these elements and taking into account the minimum frequency value of the thermal converter 1
F ₂ ≤2 ⁿ F (t ^o ) _min . (4)
The relative duration γ is determined through the duration τ of a single pulse generated at the output of trigger 9 and the frequency of the thermal converter 1 F (t ^o ) as follows
γ = τF (t ^o ).

Moreover, the duration of a single pulse is a constant and is determined by the division ratio of the counter 5
τ = k / F ₁ .

Substituting these expressions in (3), we have the resulting impulse sequence
F ₂ = F _O F (t ^{o) 2} (k / F ₁₎ ^2.

Thus, the code generated by the frequency converter to code 11, over time Θ will be defined as
N = F ₂ F (t ^o ) ² Θ (k / F ₁ ) ²
or
N = aF (t ^o ) ² ,
where a = F ₂ k ² Θ / F ₁ ² .

The output code of the frequency converter to code 11 N is uniquely associated with the measured temperature t ^o and is displayed by a digital indicator of display unit 10.

After the first T ₁ period of operation of the device, the reverse counter 4 will generate a code
N _PT (γ, N _{RG) 1} = N _RG0 + γF _{2 ^{/ F (t o) -N RG0}} F _2/2 ⁿ F (t ^o) = N _RG0 [1-F _2/2 ⁿ F (t ^o) ] + γF ₂ / F (t ^o ), (5)
where N _RG0 is the initial value of the output code, removed from register 13.

The contents of the counter 4 are recorded in the register 13 at the beginning of each period along the leading edge of the pulse-width modulated signal, and the resulting code is invariably present at the output of register 13 throughout the
N _RG1 = N _RG0 [1-F _2/2 ^{n F (t o)] +} γF ₂ / F (t ^o).

After the second T ₂ period of operation of the device, the reverse counter 4 will generate a code
N _CT (γ, N _{RG) 2} = N _RG1 + γF _{2 ^{/ F (t o) -N RG1}} F _2/2 ^{n F (t o) = {} N RG0 [ 1-F _2/2 ⁿ F (t ^o )] + γF ₂ / F (t ^o)} (1-F _2/2 ^{n F (t o)) +} γF ₂ ^{/ F (t o) = N} RG0 [ 1-F _2/2 ⁿ F (t ^o )] ² + γF ₂ ^{/ F (t o) [1+} ( 1-F _2/2 ^{n F (t o))]} .

After the ith operation period of the device, the reverse counter 4 will generate a code
_{N CT (γ, N RG)} i = N RGi- ₁ + γF _{2 ^{/ F (t o) -N RGi}} - ₁ F _2/2 ^{n F (t o) = N} RG0 [ 1-F _2/2 ⁿ F (t ^{o)] i} + γF ₂ ^{/ F (t o) [1+} ( 1-F _2/2 ^{n F (t o))]} + ( 1-F _2/2 ⁿ F (t ^{o)) 2} + . . . + (1-F _2/2 ⁿ F (t ^o )) ^i-1 ].

The second term of this expression is characterized by a geometric progression with base q = 1-F _2/2 ⁿ F (t ^o) and the first term a ₀ = 1. Thus, it can be represented by the sum S = a ₀ / (1-q), that is, S = 2 ⁿ F (t ^o ) / F ₂ .

In general, the code on counter 4 in an arbitrary period is determined by the expression
_{N CT (γ, N RG)} t = N RG0 [ 1-F _2/2 ^{n F (t o)] t} + ( 2 ⁿ F (t ^o) / F ₂₎ γF ₂ / F (t ^o) = N _RG0 [1-F _2/2 ^{n F (t o)] t} + γ2 n.

Это возможно при выполнении следующего условия
|1-F₂/2ⁿF(t^o)|<1,
или
2ⁿ⁺¹F(t^o)>F₂>0.It can be seen from the obtained expression that the result of the transformations is formed when the first term becomes equal to zero, i.e.

This is possible if the following condition is met.
| 1-F _2/2 ⁿ F (t ^o ) | <1,
or
2 ^{n + 1} F (t ^o )> F ₂ > 0.

 Given that to ensure the operability of the device with the necessary accuracy, a stricter restriction (4) is initially set, the result of the transformations is always achieved.

 Moreover, the achievement of the result is always faster than that of the prototype.

In the proposed device, the feedback action for the current period i + 1 is based only on the total values of the previous i-th period, which are fixed and held throughout the current period. In this case, the current state of counter 5 does not affect the feedback, and the increment of the code on the counter by the end of period i + 1 will be described by the expression
Δ (N _{CT i + 1} ) = Δ _{i +} -Δ _i- (N _{CT i} = N _{RG i} ),
where Δ _{i +} is the increment along the summing input of the counter 5;
Δ _i- (N _{CT i} = N _{RG i} ) is the increment at the subtracting input of the counter 5, which is constant during the period and depends on N _CTi = N _RGi .

где Δ_i+/- приращение по суммирующему входу счетчика;

приращение по вычитающему входу счетчика, которое в течение периода меняется и зависит как от N_CTi, так и от N_{ос тек ущее}.In the prototype, the feedback action for the current period i + 1 is based at the initial moment on the total values of the previous i-th period, which immediately change under the influence of negative feedback and form the current value of the result. In this case, the current state of the counter during the entire period affects the feedback, and the increment of the code on the counter by the end of period i + 1 will be described by the expression

where Δ _{i + /} is the increment along the summing input of the counter;

increment the counter by subtractor entry, which during the period varies and depends on the N _CTi, and by N _{axes uschee tech.}

 Thus, the claimed device at the end of any i + 1 period goes to a higher level of result than the prototype. As a result, in the inventive device, the value of the increments of the result to achieve the steady state at each step is greater than that of the prototype, therefore, the steady state is always achieved faster and provides accelerated processing of changes in the frequency of the output signals of the thermal converter.

Sources of information
1. USSR author's certificate 1229604. V.L. Kotlyarov, Klaus Zimmerman. Digital thermometer, cl. G 01 K 7/32, published 1986, bulletin 17.

 2. USSR copyright certificate 1520360. A.I. Gulin, S.V. Zabelina, N.M.Safyannikov and E.P. Gloomies. Digital thermometer, cl. G 01 K 7/32, declared 1987, published 1989, bulletin 41, prototype.

Claims (1)

 A digital thermometer comprising a thermocouple with a frequency output, first and second frequency generators, a reversing and summing counters, three I elements, a trigger, an indication unit, frequency converters into a code and a code into a frequency, the thermocouple output being connected to a trigger setup input, which reset the input of which connected to the transfer output of the summing counter connected by the counting input to the output of the first element And, the first input of which is connected to the output of the first frequency generator, and the second to the trigger output and with the second inputs of the second and third elements And, and the first inputs of these elements And are connected respectively the second - with the output of the second frequency generator and with the reference frequency input of the code to frequency converter, and the third - with the output of the code to frequency converter and with the subtracting input of the reverse counter , the summing input of this counter is connected to the output of the second element And, and the output of the third element And is connected to the input of the frequency converter into a code, the output of which is connected to the input of the display unit, characterized in that then a register is entered into the device, the code input of which is connected to the output of the reversible counter, the direct dynamic input of the record is with the output of the trigger, and the output is with the code input of the code to frequency converter.

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