(Prices shown are for comparison purposes only not to be construed as an offer to sell)

Laboratory Grade Electronic Readouts for PRTs (must be matched with a SPRT or PRT probe)

Automatic Resistance Bridge better than 0.1 ppm >$40,000.
Superthermometer ±0.00025C 1ppm >$15,000.
Bench Top ±0.005 $2,500
Handheld ±0.025 $1,200

Electronic Platinum Resistance Probes

SPRT (standard platinum resistance thermometer) best available accuracy
Range -200°C to 1070°C, with calibration >$6,000.
Secondary Standard PRT ±0.008°C > $1,200
Quality PRT ±0.050C >$300
Industrial PRT ± 0.050°C and up > $50

Liquid in Glass

Typically marked in 0.1°C but narrow range thermometers maybe marked 0.01°C or finer.

Thermocouples and readouts

Thermocouple Readouts to about 0.050°C $3000
Thermocouple Readouts within a few degrees $25 and up
Thermocouples range from about ±1°C to ±4°C very inexpensive to $3,000 for
Reference standard TC.

When selecting thermometers or temperature measuring equipment consider the following topics:

Accuracy

What accuracy is needed for your current application ?? It can be costly to either under or over specify this important parameter.

Range

The unit should be capable of the accuracy you require in the temperature range you are going to operate at.

Resolution

Be careful with this specification. Some readout manufacturers confuse resolution and accuracy. Having 0.001° resolution does not mean the unit is accurate to 0.001°. In general, a readout accurate to 0.01° should have a resolution of at least 0.001°. Display resolution is important when detecting small temperature changes

Linearity

Most readout manufacturers provide an accuracy specification at one temperature, typically 0°C. This is helpful, but you normally measure a wide range of temperatures, so it’s important to know the readout accuracy over your working range. If the readout were perfectly linear, its accuracy specification would be the same across its entire range. However, all readout devices have some non-linearity component and are not perfectly linear. Be sure the manufacturer provides an accuracy specification over your working range or provides a linearity specification for you to include in your uncertainty calculations.

Stability

Readout stability is important, since you’ll be making measurements in a wide variety of ambient conditions and over varying lengths of time. Be sure to review the temperature coefficient and long-term stability specifications. Make sure the variations in your ambient conditions will not affect the readout’s accuracy. Reputable readout manufacturers provide a temperature coefficient specification. The long-term stability specifications are sometimes tied to the accuracy specification—for example, "1 ppm for one year" or "0.01°C for 90 days." Calibration every 90 days is inconvenient, so calculate a one-year specification and use that in your uncertainty analysis. Be wary of the supplier who quotes ‘zero drift’ specifications. Every readout has at least one drift component.

Calibration

Some readout specifications state "no re-calibration necessary." However, under the latest ISO guides, calibration of all measuring equipment is required. Some readout devices are easier to re-calibrate than others. Look for a readout that can be calibrated through its front panel without special software. Some older readouts hold their calibration data on an EPROM that is programmed with custom software. This means the readout must be returned to the manufacturer for re-calibration—which could be in another country! Avoid readouts that still use manual potentiometer adjustments, since re-calibration is time-consuming and expensive. Most DC readouts are calibrated using a set of high-stability DC standard resistors. Calibration of an AC readout or bridge is more complicated, requiring a reference inductive voltage divider and accurate AC standard resistors.

Traceability

Measurement traceability is another concern. Traceability of DC readouts is extremely simple through well-established DC resistance standards. Traceability of AC readouts and bridges is more problematic. Many countries have no established AC resistance traceability. Many other countries that have traceable AC standards rely on AC resistors calibrated with ten times the uncertainty of the readout or bridge, which significantly increases the bridge’s own measurement uncertainty.

Convenience Features

The push for increased productivity is endless. As a result, you’ll need a readout with as many time-saving features as possible.