Test & measurement
small, simple 2-wire implementation with a fast response time, but its nonlinearity and limited temperature range limit its precision and application. An RTD is the most stable and most accurate temperature measurement method. The difficulty of RTD design is that it requires an external stimulus, complex circuits, and calibration work. Engineers without experience in developing temperature measurement systems may be discouraged. A thermocouple (TC) can provide a rugged, inexpensive solution with varying ranges, but cold junction compensation (CJC) is necessary for a complete system. Compared to the thermistor, TC, and RTD, a newly developed digital temperature sensor can provide calibrated temperature data directly through a digital interface. Precision temperature measurement requires high accuracy temperature sensors and a precision signal chain to form a temperature measurement system. TC, RTD, and digital temperature sensors have the highest accuracy. Precision signal chain devices are available and can be used to collect these sensor signals and convert them into absolute temperature. In the industrial sector, reaching 0.1°C accuracy is our target. This accuracy measurement does not include sensor errors. Table 1 shows a comparison of different temperature sensor types.
T
When creating a digital temperature measurement system, especially for applications in harsh environments such as industrial and railway, not only is accuracy and design difficulty of concern, but EMC performance is a key feature to keep the system stable. The system needs additional circuitry and discrete components to increase EMC performance. However, more protection components mean more error sources. Therefore, it is very challenging to design a temperature measurement system with high sensing accuracy and high EMC performance. The EMC performance of a temperature measurement system determines if it can work normally in the specified electromagnetic environment. ADI offers a variety of temperature measurement solutions, such as precision analogue-to-digital converters (ADCs), analogue
Temperature Sensor Type Thermistor RTD Thermocouple IC Temperature Sensor 44
emperature measurement is one of the most commonly used sensing technologies known in the analogue world. Many measurement technologies are available to sense ambient temperature. A thermistor is a
A PRECISION TEMPERATURE MEASUREMENT SOLUTION WITH HIGH EMC PERFORMANCE
USING AN RTD Have you wondered how to design a precision temperature measurement system with high electromagnetic compatibility (EMC) performance? This article from Jon Geng, applications engineer, Li Ke, system applications engineer, and Karl Wei, central applications engineer, all with Analog Devices, discusses design considerations for a precision temperature measurement system and how to improve the system’s EMC performance while maintaining measurement accuracy. It presents the test results and data analysis that allow easy movement from concept to prototype and from concept to market using an RTD temperature measurement as an example.
front ends (AFEs), IC temperature sensors, and more. ADI AFE solutions provide a multi-sensor high accuracy digital temperature measurement system for direct TC measurement, direct RTD measurement, direct thermistor measurement, and support for custom sensor applications. Some special configurations can help maintain high measurement accuracy while adding EMC protection components. Figure 1 shows the classic ratiometric temperature measurement circuit and equation.
The following sections describe temperature sensing solutions for system designers to achieve the best EMC performance.
Figure 1. Classic ratiometric temperature measurement circuit and equation.
TABLE 1. A COMPARISON OF DIFFERENT TEMPERATURE SENSOR TYPES Pros
Simple 2-wire implementation, fast response time, small size
Most stable, most accurate, rugged, easy to connect and implement
Rugged, self-powered, inexpensive, supports varying ranges (J, K, T, E, R, S, B, N), good for distance
Fully calibrated, linear, stable, analogue and digital output Cons
Nonlinear, limited temperature range, not as rugged as TCs and RTDs, requires stimulus, inaccuracies occur due to self-heating
Requires external stimulus, nonlinear, inaccuracies occur due to self-heating
Nonlinear, requires cold junction compensation (CJC), low output ranges requiring low noise/low drift electronics, accuracy 1% to 3%
Limited temperature range February 2024 Instrumentation Monthly
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