A temperature transducer is a sensor that senses temperature and converts it into a usable output signal. The temperature sensor is the core part of the temperature measuring instrument, and there are many varieties. According to the measurement method, it can be divided into two categories: contact type and non-contact type. According to the characteristics of sensor materials and electronic components, it can be divided into two categories: thermal resistance and thermocouple. What are the types of common temperature sensors? What are the main parameters? Today, I will explain it to you in detail.

Common temperature sensor models

Classification by temperature sensing elements can be roughly divided into platinum thermal resistance temperature sensors, thermocouple temperature sensors, and thermistor temperature sensors. The following small series will introduce the commonly used temperature sensor models.

Platinum RTD temperature sensor

Platinum thermal resistance is designed and manufactured by using the basic principle that the resistance value of platinum wire changes with the change of temperature. And 100 ohms (graduation number is Pt100), etc., the temperature measurement range is -200~850 ℃.

Models that use PT100 platinum thermal resistance as temperature sensing elements include armored, assembled, socket, and end-face thermal resistances.

Measurable temperature: The temperature range is -200 degrees Celsius to 150 degrees Celsius, -50 degrees Celsius to 850 degrees Celsius. It is mainly used in industries that require small temperature error or precision instruments.

Thermocouple temperature sensor

The thermocouple temperature sensor is mainly welded together by two different metal materials. If the main temperature changes, then there will be different potentials at both ends, and the corresponding temperature change is obtained through the change of the potential.

Measurable temperature: up to 2300 degrees, K-type positive grade is more accurate in high temperature section.

Thermistor

Comprised of metal oxide ceramics, it is a low-cost, highest-sensitivity temperature sensor

Temperature measurement range: the temperature range is small -50 to 200 degrees, the volume is small, and the response time is fast. Because of its low price, it has been applied to many household appliances.

Main five technical parameters

1. Accuracy

Digital temperature sensor accuracy represents the error between the sensor reading and the actual temperature of the system.

In the product specification, the accuracy index corresponds to the temperature range. There are usually several highest accuracy specifications for different temperature ranges. For the -25 to 100°C temperature range, ±2°C accuracy is common. AnalogDevice's ADT75, Maxim's DS75

2. Resolution

Digital temperature sensor resolution is a measure of how fine a sensor can detect changes in temperature. The temperature sensor integrated into the packaged chip is itself an analog sensor. All digital temperature sensors therefore have an analog-to-digital converter (ADC).

The ADC resolution will determine the overall resolution of the device, and the higher the resolution, the smaller the temperature changes that can be detected. In the product specification, the resolution is expressed in bits and in degrees Celsius. Care must be taken when considering resolution in terms of bits, as the value may or may not include the sign bit. In addition, the internal circuitry of the device

The full-scale range of the internal ADC may be determined by a value different from the overall temperature range of the sensor. Resolution in degrees Celsius is a more direct resolution value that can be used for design analysis. Existing devices have resolutions ranging from 1°C to 0.03125°C. NATIONal's LM75 is usually a 9-bit temperature sensor. Regarding the previous point, the full operating range of the LM75 is -55 to 125°C. So you might want the resolution to be 0.352°C. In practice, this resolution is specified as 0.5°C. TI's TMP102 is usually a 12-bit device with a resolution of 0.0625°C. Even small changes in ambient temperature will alert the microcontroller to take appropriate action.

3. Power consumption

Most system designers are very concerned about the total power consumption of the system, especially battery-operated systems. For digital temperature sensors used in these applications, the specified power consumption must be below the overall system power budget. Many digital temperature sensors on the market today consume only microamps of current when in operation. There are other devices on the market that have a power-down pin or power-down register function.

They may draw far less than 1mA in a powered-off state. Because system monitoring activities are often discontinuous, designers can take advantage of the "one shot" mode (which is also a feature of some digital temperature sensors). In "one shot" mode, the device is powered up just before the measurement is complete, and then resumes power down mode. With this feature, time-averaged power consumption can be minimized.

National's LM70 digital temperature sensor is a medium-low-power device that uses a power-down register. The maximum quiescent current specification in operation is 490µA, but when the device enters shutdown mode, current consumption typically drops to 12µA. TI's TMP102 uses a "one-shot" mode, so designers can easily power down the device, which typically consumes less than 1µA of current. Even when in operation, the device consumes only 10µA of quiescent current.

Another factor when considering system power consumption is the supply voltage requirements of the digital temperature sensor. The power supply voltage range required by the performance indicators of most temperature sensors is 2.7 to 5.5V. There are several devices (such as MAXIM's DS75LX) which are specially suitable for low-voltage applications, and the voltage range required by its specification is 1.7V to 3.7V. The performance of the TMP102 requires voltages as low as 1.4V.

4、Interface

Most digital temperature sensors have one of two interfaces: I2C or SPI. The I2C interface is a two-wire bus that can be used in a variety of systems that communicate with devices. It typically runs at 400kb/s, but with active termination circuits it can run at 3.4Mb/s. The bus requires a single wire with pullup plus very small. Multiple sensors can be placed on the same bus using the pins on the temperature sensor device. Some devices can be shipped with different addresses, making it easier to control several identical devices from a single I2C master. when needed in the system

Its effect becomes apparent when temperature measurements are made at several points.

SPI is a three-wire or four-wire interface, depending on whether one-way or two-way communication is required between devices. SPI does not support device addressing, so each device in the system must have a dedicated digital line connected to it. This dedicated line from the master is called chip select, chip enable or slave select, and it allows the master to communicate individually with each device.

Several digital temperature sensors currently on the market use a single-wire interface. This interface, first introduced by Maxim, is often referred to as a "single-wire" interface. Use limitations of devices, temperature sensors, etc. limit the application of this interface. Maxim's DS18B20 is a typical digital temperature sensor that utilizes a "one-wire" interface.

5、Encapsulation

Digital temperature sensor manufacturers offer a variety of package options so that system designers can readily find the right package for their system space constraints. Available package types range from 8-pin SOIC to chip scale package (CSP). Larger packages are certainly appropriate when size constraints are not a major factor in system design. CSPs are more suitable for space-constrained applications (such as cell phones), but can be difficult to manufacture. The newly listed device is a family of devices in the SOT563 package (eg TMP102). They are similar to CSPs in physical size and even height or Z dimension. But because they are packaged leaded devices, they are more robust in a production environment.

Temperature measurement is widely used. Not only the production process requires temperature control, but some electronic products also need to measure their own temperature. For example, a computer needs to monitor the temperature of the CPU, and a motor controller needs to know the temperature of the power driver IC. Temperature is a parameter that often needs to be tested in practical applications. From steel manufacturing to semiconductor production, many industrial processes rely on temperature to achieve. Temperature sensors are the bridge between the application system and the real world.

Nowadays, the temperature sensor has gradually entered the digital so-called digitization, which can convert the physical quantity of temperature and the physical quantity of humidity, through the temperature and humidity sensitive components and corresponding circuits, into a sensor that is convenient for data acquisition equipment such as computers, plc, and smart meters to directly read digital quantities.

People detect temperature in different places, and the digitization of sensors brings more convenience to people.