Classification and characteristics of temperature and humidity color paperless recorder

First, in industrial and agricultural production, meteorology, environmental protection, national defense, scientific research, aerospace and other departments, it is often necessary to measure and control environmental temperature and humidity color paperless recorders. Accurate measurement of temperature and humidity color paperless recorder is more important for bio-pharmaceuticals, food processing, paper making and other industries. In contrast, measuring humidity color paperless recorders is more complicated than measuring temperature because the temperature is measured independently, whereas humidity color paperless recorders are affected by atmospheric pressure and temperature. At present, new technologies in the field of temperature and humidity colorless paperless recorders are constantly emerging and new products are emerging.

Mainly in the following two aspects

1. The temperature and humidity color paperless recorder sensor is rapidly developing from discrete components to integrated, intelligent and systematic direction, which creates favorable conditions for the development of a new generation of temperature and humidity color paperless recorder measurement and control system;

2, in the temperature and humidity color paperless recorder measurement system commonly used linearization, automatic temperature compensation and automatic calibration humidity color paperless recorder and other new technologies.

Product classification and performance characteristics of integrated temperature and humidity color paperless recorder sensor 1.1 Integrated temperature sensor

The integrated temperature sensor mainly includes two types of analog integrated temperature sensor and intelligent temperature sensor (also called digital temperature sensor). The analog integrated temperature sensor is a dedicated IC that integrates a temperature sensor on a single chip to perform temperature measurement and analog signal output functions. The characteristics of the analog integrated temperature sensor are: single function (measurement temperature only), small temperature error, low price, fast response, long transmission distance, small size, micro power consumption, etc. It is suitable for long-range temperature measurement and temperature control. Need to perform non-linear calibration. The peripheral circuit is simple. Its typical products are AD590, AD592, TMP17, LM135 and so on.

Smart temperature sensors were introduced in the mid-1990s. It is the crystallization of microelectronics, computer technology and automatic test technology (ATE). At present, many intelligent temperature sensors have been developed internationally. The smart temperature sensor internally contains a temperature sensor, an A/D converter, a signal processor, a memory (or register), and an interface circuit. Some products also include a multiplexer (MUX), a central controller (CPU), a random access memory (RAM), and a read only memory (ROM). The characteristic of the intelligent temperature sensor is that it can output the temperature data and the related temperature control quantity, adapt to various microcontrollers (MCU); and it is based on the hardware to realize the test function through the software, its intelligence degree also depends on At the level of software development. Typical products include the DS18B20, MAX6654, and LM76.

1.2, integrated humidity color paperless recorder sensor

There are three main types of integrated humidity color paperless recorder sensors:

(1) The voltage output type integrated humidity color paperless recorder sensor is characterized by constant voltage power supply, built-in amplifier circuit, and can output volt-level voltage signals proportional to relative humidity and color paperless recorders, with fast response and repetition. Good sex, strong anti-pollution ability. Typical products are HIH3605/3610, HM1500/1520 manufactured by Honeywell, USA.

(2) Frequency output type integrated humidity color paperless recorder sensor frequency output type integrated humidity color paperless recorder sensor output frequency at 55% RH is 8750HZ (typical), when relative humidity color paperless recorder from 10 When the % is changed to 95%, the output frequency is reduced from 9560HZ to 8030HZ. This kind of sensor has the advantages of good linearity, strong anti-interference ability, easy to match digital circuit or single-chip microcomputer, and low price. The typical product is the HF3223 produced by Humirel.

(3) Frequency/temperature output type integrated humidity color paperless recorder sensor In addition to the voltage output terminal, it also adds a temperature signal output terminal, usually with a negative temperature coefficient (NTC) thermistor as a temperature sensor. When the ambient temperature changes, its resistance value also changes accordingly and is derived from the NTC end, coupled with the secondary instrument to measure the temperature. The typical product is the HTF3223 type.

1.3 Single Chip Intelligent Humidity Color Paperless Recorder/Temperature Sensing System

Recently, Switzerland? Sensiron Company has successfully developed SHT11, SHT15 intelligent humidity color paperless recorders/temperature sensors in the world. Its external dimensions are only 7.6 (mm) × 5 (mm) × 2.5 (mm), and its volume is similar to the match head. Before leaving the factory, each sensor is calibrated accurately in the humidity color paperless recorder room. The calibration coefficient is compiled into the corresponding program and stored in the calibration memory. In the measurement process, the relative humidity color paperless recorder can be automatically calibration. They not only accurately measure relative humidity color paperless recorders, but also measure temperature and dew point.

Volatile memory (RAM), status register, cyclic redundancy check (CRC) register, two-wire serial interface, control unit, heater, and low-voltage detection circuit. The measurement principle is to use two sensors to generate signals of relative humidity, colorless paperless recorders and temperature, and then send them to A/D converters for A/D conversion, calibration, and error correction. Finally, they pass the two-line string. The line interface sends the RH color paperless recorder and temperature data to μC. There is a heater inside the chip. The heater can realize the following three functions:

a By comparing the relative humidity measured before and after heating colorless paperless recorder values ​​and temperature values, it can determine whether the sensor is working properly;

b Use a heater in a humid environment to prevent condensation of the sensor;

c Heater also needs to be used when measuring dew point.

Second, the development trend of temperature and humidity color paperless recorder measurement field

2.1 extensive use of new technologies, new processes

With the advancement of science and technology, many new technologies and new processes are applied to the field of temperature and humidity colorless paperless recorders. For example, Swiss Sensiron Company uses CMOSens1 (Ce-mo-Sens) patented technology to set accuracy for high precision temperature and humidity colorless paperless recorder sensor systems. It is characterized by the integration of semiconductor chips (CMOS) and sensor technology, providing a solution for the development of highly integrated, intelligent, high-precision, high-reliability humidity color paperless recorder/temperature detection systems. This technology "Sensmitter", which represents the organic combination of sensor and transmitter. Although the SHT11/15 belongs to the sensing category, it has the innovative CMOSens1 technology that combines the functionality of a transmitter with ease. Implement system integration.

The HIH-3610 humidity color paperless recorder sensor produced by Honeywell can work normally in high temperature, chemical liquid or gas environment, for example, in a chicken shed or pig house containing harmful gases such as ammonia, benzene and formaldehyde. Relative humidity color paperless recorder. Even in saturation, the sensor can easily recover from short-term condensation. The HIH-3610 chip has a protective nitrite passivation layer that is not easily damaged during installation.

2.2 Improve Measurement Accuracy and Resolution

At present, foreign countries have introduced a variety of high-precision, high-resolution intelligent temperature sensors, the use of a 9 ~ 12-bit A / D converter, the resolution is generally up to 0.5 ~ 0.0625 °C. The DS1624 high resolution intelligent temperature sensor newly developed by DALLAS Semiconductor Company of the United States can output 13-bit binary data with a resolution of 0.03125°C and an accuracy of ±0.2°C. The HT7500 Medical Digital Thermometer IC introduced by HOLTEK of Taiwan Province of China, with a precision of ±0.1°C (or ±0.2°F), which is difficult to achieve with other thermometers (including precision mercury thermometers and digital thermometers) Technical indicators.

SHT11/15 Intelligent Humidity Color Paperless Recorder/Temperature Sensor System Measure Relative Humidity The colorless paperless recorder has a range of 0 to 100%, a resolution of 0.03% RH, and a maximum accuracy of ±2% RH. The measurement temperature range is -40°C to +123.8°C and the resolution is 0.1°C. The dew point accuracy is <±1°C. The number of digits of the A/D converter can be up to 12 bits and 14 bits when measuring humidity, color, and paperless recorders. Using a method that reduces resolution can increase the measurement rate and reduce the power consumption of the chip. The SHT11/15 products have good interchangeability, fast response, and strong anti-interference ability. They do not require external components and are suitable for various types of single-chip microcomputers. They can be widely used in medical equipment and temperature/humidity color paperless recorder adjustment systems.

2.3 increase the test function

The test function of the new smart temperature sensor is also increasing. For example, the DS1629 single-wire smart temperature sensor adds a real-time calendar clock (RTC) to make its function perfect. The DS1624 also adds a memory function that uses the chip's internal 256-byte E2PROM memory to store user's short messages. In addition, smart temperature sensors are developing from single-channel to multi-channel, which creates favorable conditions for the development and development of multi-channel temperature measurement and control systems.

In the HIH-3602C humidity color paperless recorder sensor also adds 1000Ω platinum thermal resistance, can constitute a humidity color paperless recorder / temperature measuring instrument.

2.4 Nonlinear and Temperature Compensation and Automatic Calibration Techniques

Humidity color paperless recorder sensors must be non-linear compensated and temperature compensated when measuring humidity color paperless recorders. The new intelligent temperature and humidity color paperless recorder sensor can realize automatic compensation. Take the SHT11/15 as an example, the relative humidity of the output color paperless recorder reading (N) has a nonlinear relationship with the measured relative humidity color paperless recorder (RH). When the ambient temperature TA = +25°C, the following formula can be used to compensate for nonlinearity:

(1) RH=(C1+C2N+C3N2)%=(-4+0.0405N-2.8×10-6N2)%

For example: Substituting N = 1000 into (1) formula calculates the relative humidity after compensation RH = 33.7%.

When T≠+25°C, it is also necessary to perform temperature compensation on the relative humidity colorless paperless recorder sensor. The compensation formula is (2)RHT? =RH+(T–25)·(0.01+0.00008N)%

For example, if the actual temperature T = +30 °C, using formula (2) is not difficult to calculate RHT? = 33.7% + 0.45% = 34.15%, which results in the final result of temperature compensation of a relative humidity color paperless recorder.

3. Before the SHT11/15 was shipped, each sensor was calibrated accurately in the humidity color paperless recorder room . The calibration coefficients were compiled into the corresponding program and stored in the calibration memory. In the measurement process, the relative humidity can be colored. The paperless recorder performs automatic calibration. When using a moisture sensitive resistance measurement line for a humidity color paperless recorder, the logarithmic amplifier can be used to linearize the exponential characteristic of the humidity sensitive resistance to approximate a linear relationship.

3.1 linear frequency output type relative humidity color paperless recorder measuring circuit

The HS1100/1101 incorporates the CMOS timer TLC555 to form a monostable circuit that converts a relative humidity colorless paperless recorder into a frequency signal. The output frequency range is 7351HZ to 6033HZ, and the corresponding relative humidity color paperless recorder is 0-100%. When RH=55%, f=6660HZ. The output frequency signal can be sent to a digital frequency meter or microcontroller system, and the relative humidity color paperless recorder value measured and displayed.

Circuit block diagram shown in Figure 2. Using a cheap 89C2051 microcontroller, can drive 4 LED digital tube. The frequency signal of square wave that TLC555 outputs is amplified, shaping and optocoupler isolating the circuit, send the timer of 89C2051. The keyboard can be used to set, measure or reset the program. The program is stored in the ROM of the 89C2051. The instrument measures the relative humidity. The range of the color paperless recorder is 0-100%, and the measurement accuracy can reach ±2%RH. 0.01% RH.

3.2 Relative humidity color paperless recorder/temperature test system

The circuit frame of the relative humidity color paperless recorder/temperature test system formed by the SHT15 is shown in FIG. 3 . The system can measure and display the relative humidity color paperless recorder, temperature and dew point. SHT15 as a slave, 89C51 microcontroller as a host, both through the serial bus communication. R is a pull-up resistor (can not be used), C is the power decoupling capacitor. The P0 port, P2 port and P3 port are respectively connected to 3 groups of LED displays. Among them, the measurement range of the relative humidity color paperless recorder is 0% to 99.99%, the measurement accuracy is ± 2% RH, and the resolution is 0.01% RH. The temperature measurement range is -40°C to +123.8°C, the measurement accuracy is ±1°C, and the resolution is 0.01°C. The dew point measurement accuracy is <±1°C and the resolution is ±0.01°C.