Selecting the Right Hardware

This page provides recommendations for thermocouple measurement hardware. Topics include LabJack and thermocouple selection.

LabJack Hardware Recommendations

Table 1 compares the LabJack hardware that is suitable for thermocouple measurements. More detailed hardware considerations follow.

Table 1: LabJack Device Comparison

^{[1] The T4 can measure additional thermocouples with additional LJTick-InAmp accessories, but costs rise quickly, making the T7 or U6 a better value for higher thermocouple counts.}

Highest Quality: T8

• The 24-bit sigma-delta ADCs on the T8 provide excellent measurement resolution and noise rejection.

• The 8 channel-to-channel isolated inputs help prevent measurement complications such as ground loops.

• The T8 AIN_EF system can be used to perform automatic temperature conversion for a variety of probes.

• Multiple T8s are required to measure more than 8 thermocouples; the T8 does not support any sort of analog input expansion.

• See the T8 Thermocouple Tutorial.

Minimum Cost: T4 (alt. U3) + LJTick-InAmp

• The T4 and U3 have lower resolution (12-bit ADC) than the T8, T7, or U6 devices.

• Least expensive option for 1-4 thermocouples. The U3 or T4 requires LJTick-InAmps to take thermocouple measurements. Due to the added cost per LJTick-InAmp, the U6 or T7 provides greater value for high thermocouple counts.

• See the U3/T4 Thermocouple Tutorial.

Many Channels: T7 (alt. U6) + CB37

• The T7/U6 have higher resolution (16-bit ADC) and support more channels than the T4/U3.

• Up to 14 thermocouples can be measured using one T7/U6 and one CB37 breakout board.

• The T7 AIN_EF system can be used to perform automatic temperature conversion for a variety of probes. 

• If resolution is important, the T7-Pro and U6-Pro support a higher resolution 24-bit ADC, which also features better noise rejection than the 16-bit ADC. In particular, the 24-bit sigma-delta ADCs reject 50 and 60 Hz noise, which is a common problem with thermocouple signals. Note that the noise filtering works best at lower sampling rates, and the 24-bit ADC is overall slower than the 16-bit ADC.

• Best option for low cost, many signals (4-14 thermocouples).

• See the T7 Thermocouple Tutorial or U6 Thermocouple Tutorial.

Most Channels: T7 (alt. U6) + Mux80 + 4 CB37

• The T7/U6 paired with one CB37 breakout board supports up to 14 single-ended (or 7 differential) thermocouple measurements. If you need more channels you can add the Mux80 and additional CB37 boards, which allows a T7/U6 to take up to 42 differential thermocouple measurements. Single-ended thermocouple measurements are not recommended on the Mux80.

• Lowest cost option for many signals (>14 thermocouples).

Thermocouple Hardware Recommendations

Primary considerations when selecting a thermocouple are:

• Type

• Limits of Error

• Probe Type

Type and Limits of Error

The thermocouple type can be selected based on measurement range, measurement media, and the sensor cost. Type K thermocouples are commonly used due to their low cost and wide measurement range.

Thermocouples are often designated as either class 1 or class 2. Alternatively, they may have special limits of error (similar to class 1) or standard limits of error (similar to class 2). Class 1 sensors, or sensors with special limits of error, have stricter accuracy tolerances.

Table 1 has additional information about thermocouple types and limits of error.

^{Source: https://en.wikipedia.org/wiki/Thermocouple#Comparison_of_types}

Probe Type

^{Source: https://www.omega.com/en-us/resources/selecting-a-thermocouple}

Thermocouple probes are available with the hot junction grounded, exposed, or ungrounded. Thermocouples can also be purchased as bare wire.

• Grounded probes have the hot junction grounded to the probe. Exposed probes have the hot junction exposed outside of the probe. These probe choices and bare wire can provide better response times, but could be more prone to issues such as ground loops.

• Ungrounded probes have the hot junction disconnected from the probe. This can help reduce noise, but it also dampens the sensor response time.