RU2108554C1 - Digital pyrometer of spectral ratio - Google Patents

Abstract

FIELD: instrumentation. SUBSTANCE: digital pyrometer of spectral ratio is intended for measurement of temperature of heated articles under high-temperature technological processes. Proposed pyrometer incorporates composite light filter, vibration scanner with photodetector, photocurrent amplifier, two commutators, integrator, two peak detectors, clock pulse generator, key, pulse counter, frequency divider. Given digital pyrometer of spectral ratio employs operational principle of analog-to-digital converter with push-pull integration that has lesser conversion error caused by instability of parameters of components in comparison with sweeping time pulse converter. EFFECT: enhanced operational accuracy and stability of digital pyrometer. 2 dwg

Description

 The invention relates to a control and measuring technique, namely, devices for measuring the temperature of heated products, and can be used in the manufacture of slope, forgings and building material.

Known optoelectronic systems for measuring the temperature of products with modulation of the radiation flux from a heated product (Poskachey A.A., Chubarov E.P. Optoelectronic systems for measuring temperature. M .: Energy, 1979, 88), containing logarithmic converters made on the basis of semiconductor elements - bipolar transistors. The following disadvantages are inherent in these optoelectronic elements:
1) the limited accuracy of measuring the temperature of products due to the dependence of the parameters of the semiconductor elements of the logarithmic converters on external temperature conditions;
2) the complexity of tuning and calibration of such systems due to the inability to control the characteristics of nonlinear semiconductor elements.

 The closest in technical essence to the invention is an optical-electronic device for measuring the dimensions of heated products (ed. St. USSR N 1711002, class G 01 B 21/00, 1992), containing a vibration scanner, two filters, a photodetector with a photo-current amplifier, automatic gain control unit (AGC), Schmitt trigger, the output of which is connected to the output of the photocurrent amplifier, a single vibrator connected to the Schmitt trigger, a special form of periodic signal generator, a second Schmitt trigger, the input of which is connected to the outputs of two comm utilities, and the output is connected to the control input of the third switch-key connecting the clock generator with pulse counters.

 This measuring device has a low technical level, due to its limited functionality, namely the ability to measure only a linear value-temperature correction, and with low accuracy. The main component of the temperature measurement error is determined by the error of approximating the dependence of the voltage at the output of the photocurrent amplifier on temperature, since the dependence is approximated by only one function - exponential. In addition, when converting an analog signal to a digital code, an error occurs when the Schmitt trigger comparator triggers due to the instability of the parameters of the integrating RC circuit.

 The most important task is to create a digital spectrometer pyrometer that would measure the temperature with sufficient accuracy and present the result in digital form.

 The technical result of the claimed digital spectrometer pyrometer is to increase the measurement accuracy and ease of use of this measuring device, since the measurement result is presented in a digital code. The presence of a digital output at the measuring device allows its use in automated control systems for high-temperature technological processes in various industries.

 The specified technical result is achieved by the fact that a digital spectrometer pyrometer containing two filters, filters made with different pass bands in the entire temperature range of the heated product, a vibration scanner with a photodetector located behind the filters with a scanning direction perpendicular to the filter line, the photo current amplifier, the input of which is connected to the output of the photodetector, two switches, an integrator, a peak detector, a comparator, made in the form of a Schmitt trigger, according to The clock generator, the key and the pulse counter, are equipped with a frequency divider connected to the input of the clock generator, and the output to the scanner input, an additional peak detector with an inverse output, and a trigger, while the first switch is connected between the output of the photocurrent amplifier and inputs of the peak detectors, and the second switch is between the outputs of the peak detectors and the input of the integrator, the control inputs of the switches and one of the inputs of the trigger are connected to the output of the frequency divider, the input of the comparator under is connected to the integrator’s output, and the output is to the other input of the trigger connected by the output to the control input of the key.

 This difference makes it possible to increase the accuracy of temperature measurement, since the principle of operation of an analog-to-digital converter with push-pull integration is used in a digital spectrometer pyrometer, which, in comparison with a time-pulse converter, has a significantly lower conversion error due to the instability of the parameters of the deployment element and the frequency of the clock .

 In FIG. 1 shows a block diagram of a pyrometer; figure 2 is a time-pulse diagram explaining the operation of the pyrometer.

 The pyrometer is a lens 1, in the plane of the image of which a composite filter 2 is installed, consisting of two filters with different passband and a dividing line perpendicular to the scanning direction. The spectral bandwidths of the filters are selected so that the luminous flux passing through one filter is greater than the luminous flux passing through the other filter over the entire temperature range of the heated product. For the composite light filter 2, a photodetector 3 is fixed on the scanner, which is a vibrator with an electromagnetic system 4. The vibrator 4 vibrates using an electromagnetic system to which a clock pulse generator 5 is connected via a frequency divider 6.

 A first peak detector 9 and a second peak detector 10 are connected to the photo current amplifier 7 connected to the photodetector 3, and an inverter 11 is connected to the output of the second peak detector 10. The outputs of the first peak detector 9 and inverter 11 are connected through the second switch 12 to the integrator 13, made on the operational amplifier. The control inputs of the switches 8 and 12 are connected to the output of the frequency divider 6. A comparator 14. is connected to the output of the integrator 13. It is a Schmitt trigger with a zero threshold, the output of which is connected to one of the inputs of the trigger 15, the second input of which is connected to the output of the frequency divider 6. The trigger 15 is triggered by sections of pulses arriving at its inputs. The output of the trigger 15 in turn is connected to the control input of the key 16 connecting the clock generator 5 with the pulse counter 17.

В момент времени T₁ происходит переключение коммутаторов 8 и 12 и установка триггера 15 в единичное состояние. В течение промежутка времени T₁-T, т. е. в течение времени нахождения фотоприемника 3 в зоне второго светофильтра, сигнал с усилителя фототока через первый коммутатор 8 поступает на второй пик-детектор 10, постоянное напряжение с которого через инвертор 11 и второй коммутатор 12 поступает на вход интегратора 13, на выходе которого образуется линейно убывающее напряжение (диаграмма 21 фиг. 2)

В момент равенства нулю напряжения на выходе интегратора 13 срабатывает компаратор 14, который переводит триггер 15 в нулевое состояние. Обозначив промежуток времени от начала второго такта до момента срабатывания компаратора, т. е. промежуток времени в течение которого триггер 15 находится в единичном состоянии, через переменную T₂ выразим напряжение на выходе интегратора в момент срабатывания компаратора U₁-T₁-U₂T₂ = 0. Откуда T₂ = T₁U₁/U₂, т.е. длительность импульса на выходе триггера 15 (диаграмма 22 фиг. 2) пропорциональна отношению напряжений сигналов, соответствующих разным светофильтром. Таким образом, длительность импульса пропорциональна отношению напряжений на выходе усилителя фототока, соответствующих разным светофильтрам. Напряжение с выхода триггера 15 на время T₂ открывает ключ 16 и в течение этого времени счетчик импульсов 17 считает импульсы, поступающие от генератора тактовых импульсов 5. Количество поступивших на счетчик импульсов за время T₂ (диаграмма 23 фиг.2) определяется выражением N = T₂f = T₁fU₁/U₂= K U₁/2U₂, из которого следует, что медленные в сравнении с частотой f/K изменения частоты тактовых импульсов и параметров интегратора не оказывают влияния на точность измерения отношения напряжений. Кроме того, во всем рабочем диапазоне измерения температур момент срабатывания компаратора не выходит за пределы периода T, поскольку светофильтры подобраны таким образом, что напряжение U₂ больше напряжения U₁.When the pyrometer is operating, the signal from the clock generator 5 with a frequency f (diagram 18 of FIG. 2) is fed to a frequency divider 6 with a division coefficient K. The signal from a frequency divider 6 having frequencies f / K and a period T = K / f, (diagram 19 of Fig. 2) is fed to the scanner’s electromagnetic system, by which the photodetector 3 makes a reciprocating motion, converting the spatial distribution of the brightness of the product into a temporary electrical signal, which is amplified by the photocurrent amplifier 7. The signal at the output of the photocurrent amplifier has a step step shape (diagram 20 of Fig. 2). During the time interval T ₁ = K / 2f, i.e. during the time that the photodetector 3 is in the area of the first filter, the signal from the photo current amplifier through the first switch 8 is fed to the first peak detector 9 with a discharge time constant exceeding the scanning period. Constant voltage from the peak detector 9 through the second switch 12 is supplied to the input of the integrator 13 with a time constant of τ, as a result a linearly increasing voltage is generated at the output of the integrator (diagram 21 of FIG. 2). The voltage at the output of the integrator 13 at the end of the period of time T ₁ is determined using the expression

At time T ₁ , the switches 8 and 12 are switched and the trigger 15 is set to a single state. During the period of time T ₁ -T, i.e., during the time that the photodetector 3 is in the area of the second filter, the signal from the photo current amplifier through the first switch 8 is supplied to the second peak detector 10, the constant voltage from which through the inverter 11 and the second switch 12 is fed to the input of the integrator 13, the output of which is a linearly decreasing voltage (diagram 21 of Fig. 2)

When the voltage at the output of the integrator 13 is equal to zero, the comparator 14 is activated, which puts the trigger 15 in the zero state. Denoting the time interval from the beginning of the second clock to the moment the comparator is triggered, that is, the time interval during which the trigger 15 is in a single state, through the variable T ₂ we express the voltage at the output of the integrator at the time the comparator U ₁ -T ₁ -U ₂ T ₂ = 0. Whence T ₂ = T ₁ U ₁ / U ₂ , i.e. the pulse duration at the output of the trigger 15 (diagram 22 of Fig. 2) is proportional to the ratio of the voltage of the signals corresponding to different light filters. Thus, the pulse duration is proportional to the ratio of the voltages at the output of the photocurrent amplifier corresponding to different light filters. The voltage from the output of the trigger 15 at the time T ₂ opens the key 16 and during this time the pulse counter 17 counts the pulses coming from the clock generator 5. The number of pulses received at the counter for the time T ₂ (diagram 23 of figure 2) is determined by the expression N = T ₂ f = T ₁ fU ₁ / U ₂ = KU ₁ / 2U ₂ , from which it follows that slow changes in the frequency of clock pulses and integrator parameters in comparison with the frequency f / K do not affect the accuracy of measuring the voltage ratio. In addition, in the entire operating temperature measurement range, the comparator response time does not go beyond period T, since the filters are selected in such a way that the voltage U _{2 is} greater than the voltage U ₁ .

 The result of temperature measurement can be directly entered into the computer without analog-to-digital conversion.

 The use of this digital spectrometer pyrometer can improve the accuracy of temperature measurement of products manufactured in a heated state, and therefore improve the quality of products.

Claims (1)

 A digital spectral-ratio pyrometer containing two filters made with different passband over the entire temperature range of the heated product, a vibration scanner with a photodetector located behind the filters with a scanning direction perpendicular to the filter line, a photocurrent amplifier, the input of which is connected to the output of the photodetector, two switches , integrator, peak detector, comparator, made in the form of a Schmitt trigger, serially connected clock generator, key a pulse counter, characterized in that it is equipped with a frequency divider connected to an input to a clock generator, and an output to a scanner input, an additional peak detector with an inverse output and a trigger, while the first switch is connected between the output of the photocurrent amplifier and the inputs of peak detectors and the second switch is between the outputs of the peak detectors and the integrator input, the control inputs of the switches and one of the trigger inputs are connected to the output of the frequency divider, the comparator input is connected to the integrator output, and the output to ugomu entry trigger output connected to a control input key.

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