DRY BLOCK CALIBRATOR

INTRODUCTION

A dry block calibrator, also known as a dry-well calibrator is used in accurate, liquid-free calibrations of temperature devices such as RTDs, thermocouples, bi-metal thermometers, etc.
The principle of dry block calibrator is basically very simple. “Heating up a metal block and keeping the temperature stable”.
A dry block or dry-well designs features a heated metal block, which contains a temperature controlling device as well as some type of heating element to raise the bath temperature.
The basic components of the dry block calibrator are shown below.
1.Sensor under test/calibration
2.Solid metal block (dry block)
3.Interchangeable inserts
4.Internal RTD reference sensor
5.Heating elements
6.Cooling fan

These dry-block calibrators have a removable metal insert with pre-drilled holes where sensors are inserted for calibration. The dry block insert provides a stable temperature source which can be adjusted to different test points. There are a variety of available inserts with different size and number of holes.
The sensor readings can be compared to the set temperature on the dry well or compared to a calibrated reference/master sensor. 






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Fig. 1: A typical dry block/ well calibrator

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Fig. 2: Various types of inserts

Limitations 

The maximum batch size of sensors that can be calibrated with a dry block is typically one to four. The limiting factor is the number of probes that can fit in the insert simultaneously without the probe handles/body touching each other above the dry-well as shown in figure 3.

                                  Fig. 3

Fig.4: Sensors with odd shapes & sizes

Another limiting factor of dry block calibrators is that it cannot accommodate sensors of odd shapes and sizes with transmitter heads and flanges as shown in above figure 4. To calibrate such odd-shaped sensors, a different liquid temperature bath is needed (figure 5). But compared to dry blocks, liquid baths are more expensive, bulkier and bigger in size. Also, there is always a concern of fluid spillage.

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Fig. 5: Liquid bath calibrator

The new dry block design

In order to overcome the short comings of both type of calibrators, we designed a new temperature sensor calibrator incorporating the best of both worlds.
Like a traditional dry block calibrator, it is light weight, cost effective and easier to transport to work site with added features of liquid bath mainly its capability of housing oddly shaped sensors.
Another added benefit is that there is no need of extra inserts for different sizes of sensors. Our newly designed dry block has 4 sets of six different sizes of pre-drilled holes. If needed it could calibrate in total 24 sensors at a time, thus increasing the throughput of the system.

Technical Specifications

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Testing of MVP at customer site

Setup had multiple sensors of 4 mm, 6 mm, 6.5mm and 8 mm.

Completed Dry Block Calibrator