New digital temperature sensor principle and application considerations - Solutions - Huaqiang Electronic Network

Photocoupler

Today, with the rapid advancement of sensor technology, many modern sensor companies offer new digital temperature sensors that are cost-effective, superior in performance, high in reliability, easy to use, small in size, high in sensitivity, and simple in control circuits. Features. It is a complete replacement for traditional thermistors and resistive temperature detectors.

1, the new digital temperature sensor principle

A digital temperature sensor, also called a thermocouple, is a conductor that combines two different materials or semiconductors A and B to form a closed loop. When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, both An electromotive force is generated between them, thereby forming a current of a magnitude in the loop, a phenomenon called thermoelectric effect. Thermocouples use this effect to work. Thermocouples are one of the most commonly used temperature sensing components in the industry. The advantages are: (1) high measurement accuracy; (2) wide measurement range; (3) simple structure and convenient use.

2. Application of new digital temperature sensor

The new digital temperature sensor has a wide range of applications. It is widely used not only in the daily life of ordinary people, but also in the automation control and production process detection and control systems of modern industrial production.

At present, temperature sensors in the world are developing from analog to new digital, from traditional integration to modern intelligence. Since the introduction of the new digital temperature sensor in the mid-1990s, it has also developed rapidly in China and has been rapidly applied in the daily lives of the broad masses of the people. Let's take a brief introduction to the single-chip temperature monitoring system integrated circuit (AD7416) produced by American Analog Devices.

The default parameters of the AD7416 on each power-up are as follows:

TOUI is set to 80 ° C, THYST is set to 75 ° C;

OTI works in a comparative manner;

OTI output is active low;

The fault queue length is set to 1.

These default values ​​allow the temperature sensor to act as a thermostat when not connected to the serial bus. When the measured ambient temperature is lower than THYST, OTI outputs a high level, Q1 is turned on, the relay is energized, and the heater starts to work; when the measured ambient temperature is higher than TOTI, OTI outputs a low level, which will be Q1 The base potential is pulled low to turn it off, the relay is released, and the heater stops working.

3, the new digital temperature sensor should pay attention to the following problems in practical application

In order to prevent environmental interference, the power supply of the AD7416 should be connected to a tantalum capacitor with a capacitance greater than 0.1μF.

The temperature sensing device of the AD7416 is inside the chip, so the surface of the chip is in close contact with the object to be measured;

Due to the self-consumption of the chip, the temperature rise of the AD7416 during operation is about 0.2, so a low-power mode of operation should be adopted for accurate temperature measurement;

The larger the resistance of the pull-up resistor at the OTI output, the smaller the current flowing into the AD7416, and the smaller the temperature rise, but the maximum pull-up resistor should not exceed 30kΩ, usually 10kΩ.

The I2C-compatible interface bus is always active after the AD7416 is powered up, so on-chip data can be read and written while the chip is in the sleep state.

Although the new digital temperature sensor has many advantages, in practical applications, due to the single-bus data transmission mode, the operation timing of the read and write operations is strict. Reasonable application of temperature measurement system constructed by new temperature sensor, with simple structure control engineering network copyright, high temperature measurement accuracy, convenient connection, less occupied line, fast conversion speed, simple interface with microprocessor, hardware design work belt Great convenience has been made, which can effectively reduce costs and shorten the development cycle.