To achieve the highest accuracy temperature measurement, system designers often have only one option: platinum resistance temperature detectors (RTDs), such as the PT100 or PT1000. Highly linear and interchangeable RTDs are available in a variety of accuracy class (DIN) standards such as the International Electrotechnical Commission (IEC) and the German Institute for Standardization as defined by errors as low as ±0.03°C at 0°C. However, achieving this level of accuracy with RTDs is not easy.
To obtain the highest accuracy from an RTD, it often takes hours to days to carefully select and simulate the expensive and delicate components surrounding the RTD. Designers must put a lot of effort into board layout to avoid mismatches in resistors that can affect measurements.
Despite the designers’ meticulous efforts, the acquisition Circuit can easily add 0.5°C to 1.0°C of measurement error, dwarfing the inherent accuracy of the RTD itself. To achieve accuracy close to what RTDs can provide, the only option is to calibrate each unit in production, which is time-consuming and costly.
To address the design challenges when using RTDs, TI recently introduced the TMP117 series of digital temperature sensors that offer accuracy comparable to Class-AA RTDs while greatly simplifying the design effort. As shown in Figure 1, the TMP117 provides +/- 0.1oC accuracy over the entire operating range of -55oC to 150oC, and 0.3oC accuracy from -20oC to 50oC without the need for calibration during manufacturing.
Figure 1: IEC 60751 RTD compared to TMP117 accuracy class
Note: RTD lines represent errors per IEC 60751 accuracy class, excluding measurement errors or calibrations that affect final system-level accuracy.
From a design perspective, the contrast between using an RTD design and an IC temperature sensor would not be more pronounced (see Figure 2).
Figure 2: Circuit comparison of a typical RTD with the TMP117
By combining the sensor and analog-to-digital converter (ADC) on a single chip, digital temperature sensors like the TMP117 can simplify the most difficult and time-consuming steps in RTD design and provide intuitive temperature readings through an I2C interface . Table 1 shows a detailed comparison of the required design effort between the two techniques.
Table 1: Comparison of typical design considerations between RTD and TMP117
For a platinum RTD alternative for applications requiring the highest precision, check out the TMP117. Its integration provides unprecedented simplicity while also simplifying the production process and reducing production costs.
・ For more information on this topic, see the application note “RTD Replacement in High Accuracy Sensing and Compensation Systems Using Digital Temperature Sensors”.
・ View all temperature sensor integrated circuits (ICs) from Texas Instruments.