Choosing the Best Dry Block Calibrator

Dry block calibrators have long been the tool of choice for calibrating industrial temperature sensors such as RTDS, thermocouples and thermistors. The popularity of these temperature calibrators can be linked to their portability and calibration accuracies that typically fall no more than half a degree outside the actual temperature.

Dry block calibrators consist of two primary components: A heated block and one or more interchangeable inserts. The sensor responsible for measuring and controlling the temperature is located within the heated block.

All dry blocks feature one or more holes —also known as wells— where temperature probes are placed to allow for calibration. Probes that don't fit properly in the dry block can still be calibrated by placing an insert into one of the wells.

When in the market for a dry block calibrator, it is important to consider many different factors, including accuracy, stability and flexibility.

Accuracy

Before a dry block calibrator can measure the accuracy of other temperature sensors, it must be calibrated itself. Therefore, it is important that a dry block is calibrated by a laboratory using reference thermometers traceable to the National Institute of Standards and Technology (NIST).

Calibrating a dry block with a NIST traceable temperature thermometer will ensure your device is providing accurate measurements. Don't forget to ask the manufacturer of your dry block for a NIST traceable temperature certificate.

Stability

Temperature stability around the programmed set point is also essential to the measurement accuracy of a dry-block calibrator. Fluctuations or an inability to maintain a stable temperature around the set point could result in significant measurement errors.

Flexibility

A temperature sensor immersed in a dry-block well at a considerable depth likens the chance of an accurate calibration. Most dry-blocks have removable sleeves that allow devices to be measured that otherwise don't fit properly in the holes. However, removable sleeves can bring uncertainty to the calibration reading, as it lessens the direct contact between the device and the dry block. If sleeves are necessary, one featuring multiple holes should lessen the potential for error.

One way around the configuration problem is by purchasing a dry-block with multiple wells, which will also allow multiple sensors to be calibrated at one time.

These are just some of the factors to take into consideration when shopping for a dry-block calibrator. It is important to do some of your own research to ensure you choose a dry block calibrator that properly fits with your own needs.

Mike Lala of Instrulab, is the author of this article on dry block calibrators, temperature sensors and thermocouples. Instrulab is a manufacturer of highly stable, highly accurate, Platinum RTD digital temperature instrumentation.