Measuring Temperature Accurately: What Are the Costs? (Part III)

In part two, we discussed how alternatives to mercury-in-glass thermometers performed in terms of accuracy, functionality, and limitations. Today, we assess these alternatives from an accuracy vs budget standpoint.

Greater Accuracy Requires a Bigger Budget, Usually

As is true with most instruments, greater accuracy will likely cost more when measuring temperature. Liquid-in-glass thermometers without mercury are not as accurate, so they should be used when less precision and certainty is acceptable. However, analog alternatives, liquid-in-glass thermometers, and bimetal thermometers are the most economical options, with prices, as of this writing, often under $50*. Digital indicators run approximately $50 to $100. Electronic thermometers cost more than their mercury counterparts, yet offer comparable accuracy. Digital thermometers are typically $100 and up.

Infrared thermometers ace the “cool” factor as an easy-to-use technology that uses lasers to show where the measurement is being taken. They measure surface temperature only and readings can vary based on emissivity. Because of this, accuracy can fluctuate based on the surface being measured. Entry-level infrared thermometers can range from $80 to $120. Of course, with advanced features that heighten performance capabilities, these devices can run as high as $1000.

Thermistors, RTDs/PRTs, and thermocouples all use both a meter and a probe and the combination can create varying pricing structures. For example, when adding multichannel capabilities or data logging features to the meters, their prices increase. For each of these technologies, the probes are the differentiating component and can add substantially to the cost of the system.

Generally, between thermistors, RTDs, and thermocouples, thermocouples are the most cost-effective and measure a wide range of temperatures but are the least accurate of the three. Thermocouples offer the flexibility of being available in a number of configurations and operating from a long distance without signal loss or the need for preamplification. Because of their general benefits, and reasonable-though-not-high accuracy, thermocouples can be seen as quite a value, with prices for meter and probe systems commonly $150 and up.

According to the EPA, nonmercury PRTs are as accurate as mercury-containing thermometers through a wide temperature range. RTDs/PRTs offer better stability and repeatability and are usually priced similarly to the thermistor for a standard meter and probe, which is about $200 and up. High-accuracy RTDs/PRTs are available, but the price rises steeply at more than $1000 for a system.

Thermistors are more sensitive than standard RTDs and more accurate within the biological temperature range. Thermistor systems are typically $200 and up.

For each of these systems, customized probes can be designed to meet special requirements. The cost of customization differs according to the requested needs.

*Note: Price ranges are subject to change. All suggested ranges are as of this writing.