How to Calibrate RTDs in Laboratory?

Laboratory calibration represents the highest standard of accuracy, traceability and reliability for platinum resistance thermometers (PRTs), widely applied to Class A, AA and metrology‑grade sensors that demand strict measurement consistency. As a professional expert in thermal metrology and precision temperature calibration, this article introduces the standardized laboratory calibration method using precision constant temperature baths and standard platinum resistance thermometers (SPRTs), covering working principles, multi‑point verification procedures, metrological traceability and application value, providing authoritative technical support for high‑precision temperature measurement systems. The core of laboratory calibration relies on high‑stability constant temperature baths, including water baths for low‑to‑medium temperature ranges (0 °C to 95 °C), oil baths for medium‑to‑high temperatures (up to 300 °C) and cryogenic baths for sub‑zero environments. These baths deliver excellent temperature uniformity and stability, with fluctuation typically controlled within ±0.005 °C, creating an ideal thermal field for precision calibration. Paired with Class 0 or Class 1 standard platinum resistance thermometers, which are directly traceable to national and international metrology standards, the system establishes a fully traceable reference chain complying with ITS‑90 international temperature scale specifications. During formal calibration, multi‑point temperature verification is performed at key reference points, most commonly 0 °C, 100 °C and 200 °C, covering typical industrial and laboratory operating ranges. The sensor under test and the standard platinum resistance thermometer are placed in the same constant temperature bath, with sufficient soaking time to ensure complete thermal equilibrium. A high‑precision resistance bridge or digital multimeter measures the actual resistance of the tested PRT, which is then compared with the standard resistance value derived from the SPRT and ITS‑90 formula. The system calculates absolute error, linearity deviation, drift and conformance to tolerance class, forming the basis for calibration evaluation. This method delivers the highest measurement accuracy and the most authoritative results, far exceeding on‑site calibration techniques. It can identify subtle resistance drift, non‑linearity errors and performance degradation caused by high‑temperature cycling, mechanical stress and insulation aging, which are difficult to detect through field checks. After calibration, a formal calibration certificate is issued, recording test data, error values, environmental conditions and metrological traceability paths, supporting quality system audits, customer acceptance and regulatory compliance. Laboratory calibration is specially designed for high‑precision applications, including metrology laboratories, national verification institutions, aerospace testing, pharmaceutical manufacturing, semiconductor processing and precision thermal control systems. It is the only valid method for certifying Class A, AA and ultra‑precision metrology‑grade platinum resistance sensors, ensuring their measurement data meets mandatory metrological regulations and industry specifications. In summary, constant temperature bath and standard platinum resistance‑based laboratory calibration is the gold standard for precision PRT calibration. It achieves full metrological traceability, quantifies detailed performance indicators and provides authoritative, certified test reports. For applications where temperature accuracy directly affects product quality, process safety and regulatory compliance, this method is irreplaceable, ensuring long‑term stability and traceable accuracy of high‑grade platinum resistance temperature sensors.