Design, Construction, and Calibration of a Temperature Monitoring System for Resistance Standards

We present the design, construction, calibration, and software development of a temperature monitoring system for resistance standards. The system supports 19 temperature probes. Over the range 295.15 K to 299.15 K (22 °C to 26 °C), we report an expanded uncertainty (k = 2) of 9 mK. With the addition of a calibrated standard reference thermometer and a programmable oil bath, the system was used to automatically calibrate the temperature probes over this 4 K range. In continuous operation, this system supplies a constant current to thermistor temperature probes and a reference resistor, and it measures the voltage across them. The ratio between each of the probe voltages and the reference voltage is multiplied by the reference resistance to determine the resistance of each probe. To reduce systematic errors, voltage measurements are taken with the current running in alternating directions. Finally, using the Steinhart-Hart model, the probe resistances are converted to their corresponding temperatures and recorded to a secure network drive. If a probe reads a temperature outside of the desired temperature range for its location, an email alert is sent to all the staff who work in the laboratory. An additional message will be sent to facility services if the probe is measuring the room temperature in the laboratory. The system was developed for the NIST resistance laboratory, but it could easily be duplicated for use in any laboratory environment where continuous temperature monitoring in multiple locations with expanded uncertainty (k = 2) of 9 mK is needed.