Chapter 220 - Digital Temperature Sensors in the Range of 77-300 K

Abstract

This chapter investigates the digital sensors of temperature (integrated circuits) manufactured by Analog Devices (AD7416) and National Semiconductor (LM74). The investigations cover both the lower limits of the operate temperature of digital sensors and measurement accuracy. The testing of sensors realized on a sample of AD7416 and LM74 integrated circuits showed that digital temperature sensors preserve their working ability in temperature much lower than that defined by the manufacturers. AD7416 sensors operate as low temperature as –128ºC (145 K). Their measurement error was below ±2ºC Lower limit for LM74 sensors was different for two investigated sensors: –140ºC and –70ºC. The accuracy is of 5ºC at temperature below –100ºC. None of the sensors were able for a work at the temperature as low as 77 K. Single devices of digital temperature sensors may be therefore used to construct cryogenic thermometers of less accuracy. It is useful especially in such measurements in which a signal from analog sensor is notably distorted, for example by a strong electromagnetic field.