temperature detector of choice and the choice of transmitter to consider the scope and accuracy of temperature control. 0~1000 ° C for the measurement using thermocouples, such as nickel chromium thermocouple, Graduation for the EU. 0~41.32mV output signals, millivolt transmitter output 0~10mA. -- then read current voltage conversion circuit voltage op. To improve the measurement accuracy of 0.1 for transmitter can be relocated. changed 400~1000 ° C temperature range, given 16.4~41.32mV thermocouple, Transmitter output 0~10mV so that the use of 8-bit ADC, quantization error of ± 2.34 ° C make. 2. Due to the expansion of the system interface chip to show both the police and keyboard input, but also control, Therefore, the expansion of the system in 8031 was 8,155, which has three eight Interface. 256 bytes of RAM can be used as an external data storage for the system. 8031 P2.1 accept the CE 8155, then 8155's P2.0 IO/M. When P2.1=0, P2.0=1, the three films selected 8,155 / port, port addresses are as follows :Register 0101H 0100H [] [] A state order mouth I 0103H 0102H [B] [C] I control the population register or low numerical terms eight 0105H 0104H [] [] high eight dollars and numerical methods Register When P2.2=0, selected ADCO8O9 (allowing access conversion and start reading the results of conversion). EOC signal conversion by the end of inverter followed disruption to the external MCU INT1 (P3.3). When P3.3=0, to translate the end. We will use as input channel 0, 0809 as a 03F8H address of the external data storage unit its written data, the WR 8031 and the START ALE signal so effective, 74LS373 latch the address will be deposited in three low 0809 and started ADCO8O9. D. 9EOC of low level, ongoing D conversion, switching to the EOC, said the end of conversion, 8031 can be read as good data conversion. 3. Temperature control circuit temperature control circuit Thyrister-way. Triac Series 50Hz AC power and heating wire in the circuit. If change thyristor switches in a given cycle time of the pulse signal can be connected. This can be one / line through export control procedures pulse.
To achieve zero trigger the end, AC zero-crossing detection circuit. 50Hz AC voltage corresponding to the circuit output pulse zero moment, as the simultaneous bidirectional thyristor trigger pulse, thyristor make the AC voltage zero conduction time. LM311 voltage comparator to 50HZ AC voltage into a square. Square, as the rising or
falling transition triggered monostable multivibrator signal Trigger pulse output stability of the single narrow door on the diode or mixed 220V power -- be it corresponds to the zero-crossing time synchronization pulse. This way as a trigger pulse synchronization pulse upon the temperature control circuit. SCM 8031 as a way of counting pulses added to the P3.4 and P3.5 input. (3) the laws and procedures designed to control the Resistance Heater Control is a feedback process Temperature and Temperature needs to be more practical deviation of the error signal processing controlled, The power to regulate the resistance furnace, the furnace temperature control to achieve.According to the error ratio, integral and differential have control (PID). process control is the most widely used form of a control. PID is the approximate difference equations using computers to achieve. PID law equation (abbreviated). Interrupt nesting mode using dual control system design process.
First make T0 Counter regularly interrupted, as the system's sampling period. D process started in a break in service, reading the data sampling, digital filtering, on the threshold alarm, PID, and then pulse output control signals. T1 pulse width counter overflow interrupted by the decision. T1 suspended pending, this sampling will be converted into the corresponding temperature display buffer. Then call display subroutine. T1 return from the suspension, then returned to the main program and suspended from T0, continue to show this sample temperature T0 waiting for the next interruption. Since 1976, Intel introduced the first batch of SCM, SCM technology into the 1980s, the period of rapid development in recent years, with the development of large-scale integrated circuits. SCM will continue rapid development of high-performance, four, 8-bit MCU to 16-bit and 32-bit MCU. SCM mainly used to control its application across the board, to the space shuttle, small refrigerators to daily life. color televisions, big MCU can display their talents. SCM in the three areas are very broad application : The first is household appliances industry, such as automatic washing machines, smart toys; Second, the communications industry, including telephone, cell phone and pager, etc.;The third is to create instrumentation and computer peripherals, such as floppy disks, hard disks, cash registers, meters. In addition to these traditional spheres, automobiles, electronics industry and foreign SCM application is a very broad field. It is low cost, high integration,
low power and control functions into a more flexible assembly of intelligent control devices. by the intelligent instrument it constitutes a long time to resolve the errors of measurement instruments, linear address other issues. SCM will microprocessor, memory, timer / counter, / interface integrated circuit on a chip of large-scale integrated circuits, the computer itself is a small system. SCM technology and sensor technology, and signal analysis technology, circuit design technology programmable logic technology, computer interface technology, database technology and data structure of the computer operating system, assembly language programming, high-level language programming, software engineering, data communication networks, digital signal processing, control, Error analysis, instrument design and manufacturing techniques, etc., and makes extensive use of the MCU. Meanwhile, SCM has strong management functions. Single chip measurement circuit of the entire management and control, which makes the system intelligent, and low power consumption. less use of electronic components and internal wiring small, low cost, manufacturing, installation, commissioning and maintenance convenience.
Temperature sensors will be converted into electricity measured temperature, after amplification circuit filter processing, ADC conversion from analog to digita
l, connected with the MCU. Programmable keyboard and display interface to the chip set temperature limits. Finally, the small keyboard control LED shows need a road temperature. 1. After measuring the temperature sensor has been converted to electricity and then gave amplified ADC.
2. After conversion of binary-D numerical electricity, gave 8031. According to the 8031 software is designed to accomplish.
3. Disposed, sending keyboard and display processing chips, and then from Digital Display.
4. If the temperature exceeds limits established by the temperature, turn alarm processing. 5. Small ones from the keyboard shows the temperature control requirements.
The choice of sensors used mainly thermocouple temperature detector, thermal resistance, thermal resistance, etc.. Thermocouple mainly using the thermoelectric effect of two different metals have potential contact with the temperature change, which Temperature in
order to achieve the objective. Accurate measurement, temperature measurement moderate price range, linearity better. However, its output voltage by the end of the cold temperature, the need for cold temperature compensation, the circuit complexity China is not the best option in this issue. Thermistor or metal oxide semiconductor materials by high sensitivity, small thermal inertia, long life, low prices. But measuring the stability and repeatability is poor, unable to meet the measurement accuracy of 0.2 ° C to give some of the requirements. Poor linearity and the need for look-up table linear regression, a lot of waste of resources controller, it is not selected. The thermal resistance is the use of metal resistivity with temperature changes and changes in the characteristics of temperature into volume resistivity volume. The advantage is high accuracy and high stability, high reliability, small thermal inertia, rehabilitation is good, moderate price. It is linear with temperature resistance, thermal resistance Pt100, 0 \℃ expressed by the following equation :Which A=3.9083 ╳ 10-3 / ;B=-5.775 ╳ 10-7 ° C / ° C; This shows that The higher the temperature the greater the non-linear error, the scope of this topic demands Temperature -90 ° C and 40 ° C, lower temperatures. When the calculated temperature of 90 ° C, nonlinearity error of 0.34%. The least square method is suitable for 0.1 and gain adjustment, but also to make the same error twice reduced and the accuracy of the stated requirements. 0.2/90=0.22%, this issue should be selected Pt100 resistance, Approximate values and temperature resistance can be seen as linear.
2, amplifier thermal resistance measured resistance is the amount needed to be translated into voltage controller can be collected. Basic resistance-voltage conversion circuit is fixed with another series resistance, but this way, When the output level for non-zero temperature range, is not conducive to the small signal amplification and D conversion accuracy. Therefore, the use of bridge work measurement circuit which is shown in figure 2 : R1R2 Ω for a fixed voltage resistance, Rt thermal resistance, Rw2 to zero resistance, as the two make it the same way current and keeps constant, output voltage adjustable Rt0=Rw2, which makes R1 bridge in the great output avoids making small changes. When the Rt changes from 0 to 100 ° C, only 10 mV output, it still needs to conduct small-signal amplification. The works are low-frequency gain adjustable amplifier circuit in
Figure 3 :Rw1 to gain resistance which, adjusted for measuring full range, low-noise operational amplifier used NE5532. Order R2, R3=R4, R5=R6, then the total gain amplifier. When Rw1 from 0 to 50k Ω change, ∞ Av changed in the range of 150 to meet the requirements necessary gains.
3, D conversion subject to the requirements of measurement accuracy of 0.2 ° C degrees. Temperature should be the scope of the requirements for the maximum temperature to room temperature, 20 to 90 ℃. This determines the minimum resolution of not less than 0.2/ D conversion (90-20) =1/350. D conversion chip can reach ordinary eight 1/256 not meet the requirements. If the chips use a higher place, it will greatly increase the cost. Is a time constant temperature changes in the larger variables, D conversion rate of a modest, therefore, the design was chosen VCO first voltage signal into a frequency volume, Counting through the controller function into a digital signal, which could greatly improve the accuracy and cost savings.
4, the temperature controller error feedback control it will be used classical control theory of PID (Proportional Integral and Derivative proportional integral differential) control, the controller can take a number of options, such as analog circuits. microcontroller, such as logic devices. Analog circuit can be controlled to change for the error control technology is mature, more stable performance. However, the drawback is not easy, tuning PID parameters need replacement parts, and vulnerable to outside interference. Now in the digital era has become highly developed eliminated. SCM as a branch of micro-computer, and more than 20 years of development, have a wide range of applications in the field of control. Moreover, in recent years, with the FPGA (field programmable gate array) has been engaged to represent the programmable logic device. SCM makes up for their excellent performance significantly slower to respond, the less disruption source shortcomings. However, the FPGA computing capacity is limited, therefore, we used in the design of the FPGA and microprocessor control method combining two complementary strengths, greatly improving performance. In the book, the VCO signal FPGA is mainly responsible for receiving, and the pulse is obtained by measuring its voltage; SCM receiving FPGA transmitted data and show that PID operation, and output
5, the output drive circuit PID controller to the computational results
into different pulse duty cycle output The agencies also need to read the signals role in the implementation of drive circuit. The AC power control circuit works, about a few cycle load connected with the AC power supply, and calls for a few cycle. open and continuous cycle by changing the ratio of the average power consumption load regulation. Specific circuit in Figure 5. 220V/50Hz power to the city, to 5V voltage division below, the input operational amplifier with an input. Operational Amplifier as a zero comparator, when electricity over night, jumping changed operational amplifier output to the clock terminal D flip-flop, SCM then the output of D flip-flop input pulse signal, the output of two-way thyristor gate. Thus, only when the AC off night, SCM thyristor output signal only have an effect in other words, Only when the AC off night, or turn-off thyristor can be opened. This can greatly reduce the opening-off thyristor impact on the process, reduce opening-off loss.