Fully Automated Thermometer Calibration System at the Standards and Calibration Laboratory (SCL)

Abstract

Traditionally, thermometers are calibrated by comparison with reference thermometers, such as standard platinum resistance thermometers in liquid baths. The process is time consuming and costly since an operator is required to adjust the bath temperature and take the readings of the thermometers. The Standards and Calibration Laboratory (SCL), Hong Kong Special Administrative Region recently developed a fully automated calibration system for thermometer calibration which does not require the attention of an operator. The system makes use of a computer to control the bath temperature and take the thermometer readings by using pattern recognition techniques. Optical Character Recognition (OCR) and Liquid Level Recognition (LLR) techniques are employed to take the readings of the digital and liquid-in-glass thermometers respectively. The reading process starts with taking pictures of the display of the thermometer under test by a smart video camera. The images are analyzed by Labview based programmes to find the thermometer readings. The system can be trained to recognize various display formats of the thermometers under test. The images of the display readings are retained for proof checking when a report is produced.