Sobre o design e aplicação do sistema de medição de temperatura do sensor de termopar

Como um elemento de medição de temperatura típico, o sensor de termopar tem sido amplamente utilizado .
A seguir, é apresentado um sistema de medição de temperatura típico controlado por um único microcomputador de chip, que consiste em três partes: (1) circuito do amplificador de medição; (2) circuito de conversão A/D; (3) Circuito de exibição . É amplamente utilizado em sistemas de medição e controle de temperatura em usinas de energia e plantas químicas .
1. design de hardware
(1) Sensor de temperatura do termopar
This system uses nickel-chromium-nickel-silicon thermocouples. The measured temperature range is 0-655℃. The cold end compensation adopts the compensation bridge method. The potential generated by the unbalanced bridge is used to compensate for the change in thermoelectric potential caused by the change in the cold end temperature of the thermocouple. The unbalanced bridge consists of four bridge arms of resistors R1, R2, R3 (manganese copper wire winding), Rcu (copper wire winding) and a bridge voltage regulator, which are connected in series in the thermocouple circuit. Rcu and the cold end of the thermocouple are at ±0℃, and R1=R2=R3=1Ω. The bridge power supply voltage is 4V, powered by a voltage-stabilized power supply. Rs is a current-limiting resistor, and its resistance value varies with different thermocouples. The bridge is usually balanced at 20℃. Neste momento, as quatro resistências do braço da ponte da ponte são r 1= r 2= r 3= rcu, e não há saída em que a temperatura térmica é que a temperatura de temperatura fins a e b . quando a temperatura fria se desvie de 20 graus, para o exemplo, quando o B -b . À medida que a temperatura da extremidade fria aumenta . UAB é igual à diminuição do potencial termoelétrico, e o potencial de saída permanece inalterado após a UAB ser sobreposta ao potencial termoelétrico, alcançando assim a conclusão automática da compensação de extremidade a frio .
(2) circuito do amplificador de medição
Nos circuitos reais, a saída do sinal do termopar não passa de algumas dezenas de milivolts (<30mV), and contains common-mode interference such as power frequency, static electricity and magnetic coupling. To amplify this kind of circuit, the amplifier circuit needs to have a high common-mode rejection ratio, high gain, low noise and high input impedance. Therefore, a measurement amplifier circuit is suitable. The measurement amplifier is also called a data amplifier, instrument amplifier and bridge amplifier. It has a high input impedance and is easy to match with various signal sources. Its input offset voltage, input offset current and input bias current are small, and the temperature drift is small. Due to the small time temperature drift, the measurement amplifier has good stability. The measurement amplifier is composed of three op amps, and the differential input terminals R1 and R2 are connected to the in-phase terminals of A1 and A2 respectively. The input impedance is very high, a symmetrical circuit structure is used, and the measured signal is directly added to the input terminal, thereby ensuring a strong ability to suppress common-mode signals. A3 is actually a differential follower, and its gain is approximately 1. The gain of the measuring amplifier is: AV=V0/(V2-V1), AV=Rf/R(1+(Rf1+Rf2)/RW). In this circuit, as long as the performance of op amps A1 and A2 is symmetrical (mainly referring to input impedance and voltage gain), their drift will be greatly reduced. They have high input impedance and common mode rejection ratio, are very sensitive to tiny differential mode voltage, and are suitable for measuring signals transmitted over long distances. Therefore, they are very easy to use with sensors with tiny outputs. RW is an external resistor used to adjust the gain, and a multi-turn potentiometer is used here.
In the actual circuit, A1 and A2 use low-drift, high-precision op amp OP-07 chips, whose input offset voltage temperature drift VIOS and input offset current temperature drift IIOS are very small. OP-07 uses ultra-high technology and "Zener fine-tuning" technology to make its VIOS, IIOS, VIOS and IIOS very small, and is widely used in stable integration, precision addition, comparison detection and precision amplification of weak signals. OP-07 requires dual power supply, and the operating temperature range is 0-70℃. Generally, zero adjustment is not required. If zero adjustment is required, RW can be used for Ajuste . A3 usa o chip 741, que requer fonte de alimentação dupla, e a faixa de fonte de alimentação é ± (3-18) v . A fonte de alimentação típica é ± 15V, que geralmente deve ser maior ou igual a ± 5V .} It contém compensa que o capacm. requerido .
(3) Circuito de conversão A/D (Analog-to-Digital)
O sinal de tensão amplificado pelo amplificador de medição possui uma faixa de tensão de 0-5 v . Este sinal é um sinal analógico e não pode ser aceito pelo computador; portanto, a conversão A/D deve ser executada . no circuito real, o iCl7109 Chip is Selected .}} » low-noise, low-drift, low-cost dual-integral 12-bit A/D converter. Since the current 12-bit successive approximation A/D converter is relatively expensive, the cheap dual-integral 12-bit A/D converter ICL7109 can be used in situations where the speed is not too high, such as in Sistemas de medição de alta precisão para vários sinais de sensor, como pesagem, pressão de medição e temperatura de medição .
Através da análise acima do sistema de medição de temperatura do sensor de termopar, espero que seja útil para o trabalho e o estudo de todos .