A Micro-Computer Based System for High Precision Temperature Measurement Using Platinum RTD's

A micro-computer controlled system for 10 channel high precision temperature data acquisition has been developed. The temperature sensing elements are Platinum Resistance Thermometer Devices RTDs. Probe construction, using standard, commercially available RTD elements is described and wiring and switching requirements for the 4-wire resistance measurements are noted. The system consists of a Digital Equipment Corp. MINC-11 Computer linked, via IEEE-488 interface bus cables, to a HP Hewlett-Packard 34555A Digital VoltOhm Meter, an HP-3495A ScannerMultiplexer, and, during calibration, a HP 2804A Quartz Thermometer. Two programs are employed one for probe calibration and the other for the temperature measurement application. In the calibration program, the ten probes are individually calibrated against the Quartz Thermometer which has an absolute accuracy specification of or - 0.04 C. A proportional control water bath having a thermal stability specification of or - 0.004 C provided the common thermal medium during calibration. Currently a three point calibration spanning 6 C 37 to 43 C is employed. The individual probe constants are computed and recorded on a computer file for access via the temperature measurement program. An initial evaluation of the precision of the calibrated RTD system against the Quartz Thermometer reading yielded an overall precision of or - 0.0004 C and worst case error of less than or - 0.01 C.