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Thermometry Bridges

Characterisation of a selection of AC and DC resistance bridges for standard platinum resistance thermometry

An NPL study of the performance of 14 resistance bridges which were available for testing at NPL, consisting of a range of manufacturers and types, has been evaluated and expressed in terms of the standard deviation of the bridge errors over a given range of ratios, namely s.
Thermometry Bridges

How to Calibrate Thermometry Bridges: Ensuring Accurate Temperature Measurements

Published in Cal Lab Magazine and reproduced with permission; this article looks at the calibration of thermometry bridges. Thermometry bridges play a crucial role in temperature measurement, particularly when it comes to the interpolation of the Standard Platinum Resistance Thermometer (SPRT) specified by the ITS-90. However, to achieve precise and reliable results, it is essential to calibrate these bridges accurately.

Double Junction Thermocouple: What is it and how can it be used?

The accuracy of the Cold Junction Compensation (CJC) sensor in a temperature indicator is critical in order to make accurate measurements with thermocouples. Read our white paper exploring cold junction compensation, how to improve accuracy and calibrate using double junction thermocouples, and using a double junction to calibrate thermocouple indicators with electrical stimulation.

Automation of Temperature Calibration

The automation of temperature calibrations has become more widespread in recent years as the demand from industry has grown and workloads have increased. Significant time savings and the ability to produce tailored calibration certificates has enabled the metrology community to actively service this need. Here, we show the equipment required and the configuration to automate the calibration-by-comparison of thermocouples and platinum resistance thermometers in the temperature range -20°C to +140°C.

Standard Resistor Calibration

Highest accuracy temperature measurements rely on the best SPRTs, Thermometry Bridges and Standard Resistors. For the standard resistors, it is vital that they have a low calibration uncertainty. Isotech are able to calibrate your primary standards to the lowest of uncertainties. With our priority booking-in service, turnaround times can be as low as one week!

Platinum Resistance Thermometer: Self Heating

With resistance thermometers careful consideration should be given to the measuring current in order to minimise the "self-heating effect". A look at the construction of platinum resistance thermometers and how to determine and correct for this effect.

Strain in Standard Platinum Resistance Thermometers

When an SPRT is strained, the platinum is being stretched and thinned (like a strain gauge) and the resistance increases. By heating the thermometer (annealing) and then cooling it in a controlled way, the crystal lattice of the platinum returns to its original condition and the resistance of the thermometer reduces. Annealing should be seen as part of the maintenance of a thermometer.

Cold Junction Thermocouple Probes

How to Electrically Calibrate a Temperature Indicator that has Cold Junction Compensation? When calibrating a thermocouple indicator that has cold junction compensation, a standard voltage generator cannot be directly connected to the thermocouple input. One method is to connect the voltage generator to a “double junction” of thermocouple to copper wires and to place this junction in an ice flask or 0 °C reference unit.

Why Use a Standard Platinum Resistance Thermometer (SPRT)?

Industrial PRTs can have uncertainties of around 0.01 °C at 0 °C, with relatively low cost and are more rugged than Standard Platinum Resistance Thermometers. When lower uncertainties are needed Standard Platinum Resistance Thermometers can be used. Primary SPRTs are constructed in such a way that the platinum wire coil is free to expand and contract without strain. The flipside of the performance benefit is that the SPRTs are very fragile and require very careful handling. Primary SPRTs need the most care, whilst secondary or working SPRTs still need careful handling they are less prone to mechanical shock and can still be calibrated to low uncertainties, typically 0.001 °C at 0 °C and 0.006 °C at 660 °C.
Water Triple Point

The Establishment of ITS-90 Water Triple Point References to ±2uK, and the Assessment of 100 Water Triple Point Cells Made Between 2001 and 2006

This article presents data from a group of water triple point cells made from a still designed to produce pure, air free water of isotopic composition close to V-SMOW.