Chapter 1 Introduction 1. 1 Topic Background Moisture-proof, mildew-proof, anti-corrosion and explosion-proof are important contents of the daily work of the warehouse, and are also important indicators to measure the quality of warehouse management. It directly affects the service life and working reliability of reserve materials. In order to ensure the smooth progress of daily work, the first problem is to strengthen the monitoring of temperature and humidity in the warehouse. The traditional method is to use hygrometer, hair hygrometer, bimetal meter, humidity test paper and other testing equipment to ventilate, dehumidify and cool the warehouse that does not meet the temperature and humidity requirements through manual testing. This manual testing method is time-consuming, laborious and inefficient, and the temperature and humidity tested have great errors and randomness. Therefore, we need a temperature and humidity measuring instrument with low cost, convenient use and accurate measurement. 1.2 design process and technological requirements 1. Basic functions ~ temperature and humidity detection ~ temperature and humidity display ~ overrun alarm 2. Main technical parameters ~ temperature detection range: -30℃-+50℃~ measurement accuracy: 0.5℃~ humidity detection range: 10%- 100%RH~ detection accuracy: 1%RH~ display mode: temperature: four-position display humidity: four-position. Chapter 2 Comparison and Demonstration of Triode-driven Buzzer Alarm Scheme When a single chip microcomputer is used as a measurement and control system, the system must always have the measured signal to understand the input channel, and the computer will pick up the necessary input information. For the measurement system, how to obtain the measured signal accurately is its core task; For the measurement and control system, it is also essential to detect the state of the controlled object and monitor the control conditions. Sensor is the first step to realize measurement and control, and it is the key component of measurement and control system. Without the accurate and reliable capture and conversion of the original measurement signal, all accurate measurement and control will not be realized. The automatic measurement and control of industrial production process almost mainly depends on various sensors to detect and control various parameters in the production process, so that the equipment and system can operate normally in the best state, thus ensuring the high efficiency and high quality of production. 2. 1 temperature sensor scheme 1: thermal resistance temperature sensor is adopted. Thermal resistance is a temperature measuring element made by using the characteristics of conductor resistance changing with temperature. Platinum, copper, nickel and other thermal resistors are widely used. Its main features are high precision, wide measuring range and convenient for long-distance measurement. Platinum has extremely stable physical and chemical properties, strong oxidation resistance, easy purification, good reproducibility, good industrialization and high resistivity. Therefore, platinum resistance is used for high-precision temperature measurement and temperature standard in industrial detection. Disadvantages are high price, low temperature coefficient, great influence by magnetic field, easy contamination and fragility in reducing medium. When the temperature range is -200 ~ 650℃ according to IEC standard, and the Baidu resistance ratio W( 100)= 1.3850, R0 is100Ω and10Ω, and the allowable measurement error is Class A (0./kloc-0 The temperature coefficient of copper resistance is higher than that of platinum resistance, which is low in price and easy to purify and process. However, its resistivity is small and its stability in corrosive medium is poor. It is used to measure the temperature of -50 ~ 180℃ in industry. Scheme 2: AD590 is adopted, and its temperature range is -55℃ ~+ 150℃, with high accuracy. In the range of temperature measurement, the nonlinear error of M range is 0.3℃. The AD590 can withstand 44V DC voltage and 20V reverse voltage, so the reverse connection of the device will not be damaged. Reliable use. It only needs DC power supply to work without linear correction, so it is very convenient to use and the reason is simple. As a current output sensor, one of its characteristics is its strong anti-interference ability compared with a voltage output sensor. The measuring signal of AD590 can be transmitted over 100 meters. Comparing scheme 1 with scheme 2, scheme 2 is more suitable for the selection of temperature sensors in this design system. 2.2 Selection of humidity sensor There are many ways to measure air humidity. Its principle is to indirectly obtain the water absorption of the substance and the humidity of the surrounding air according to the change of physical or chemical properties caused by the absorption of water from the surrounding air. Capacitive, resistive and swelling humidity sensors measure humidity according to the changes of dielectric constant, resistivity and volume of polymer materials after moisture absorption. Scheme 1: HOS-20 1 humidity sensor is adopted. HOS-20 1 humidity sensor is a high humidity switch sensor. Its working voltage is below 1V AC, frequency is 50hz ~ 1KHz, measuring humidity range is 0 ~ 100% RH, working temperature range is 0 ~ 50℃, and impedance is 75%RH(25℃). This kind of sensor was originally used for switching, so it can't detect humidity in a wide frequency band, so it is mainly used to judge whether the humidity level is higher or lower than the specified value. However, this kind of sensor has good linearity only when it is used in a certain range, and its linearity can be effectively utilized. Scheme 2: adopt the humidity sensor of HS1100/HS11. Hs1100/hs11capacitive sensor is equivalent to a capacitive device in circuit composition, and its capacitance increases with the increase of air humidity. Complete interchangeability without calibration, high reliability and long-term stability, fast response time, patented solid polymer structure, consisting of top contact (HS 1 100) and side contact (hs11), suitable for linear voltage output and frequency output circuits. The relative humidity is in the range of 1%- 100% RH; The capacitance is changed from 16pF to 200pF, and the error is less than 2% RH. The response time is less than 5s; The temperature coefficient is 0.04 pF/℃. It can be seen that the accuracy is high. Comparing the first scheme and the second scheme comprehensively, although the first scheme meets the requirements of accuracy and humidity measurement range, it has good linearity only when it is used in a certain range, and its linearity can be effectively utilized. Moreover, the design system does not meet the requirements of -30 ~ 50℃, so we choose the second scheme as the humidity sensor in this design. 2.3 Selection of signal acquisition channels In this design system, the temperature input signal is 8 analog signals, which requires multi-channel structure. Scheme 1: Multiple parallel analog input channels are adopted. The analog channel of this structure is characterized in that (1) devices with different performance levels can be selected according to the requirements of various input measurements. The total cost can be reduced. (2) The hardware is complex and the failure rate is high. (3) The software is simple, and each channel can be programmed independently. Scheme 2: Multi-channel time-sharing analog input channels are adopted. The analog channel with this structure is characterized by: (1) high requirements for ADC and S/H; (2) slow processing speed. (3) Simple hardware and low cost. (4) The software is complex. Comparing the first scheme and the second scheme comprehensively, the second scheme is more suitable for the requirements of analog input in this design system, and comparing its block diagram, the second scheme has the outstanding advantage of simple hardware, so the second scheme is chosen as the signal input channel. This article comes from: /dianzi/