Improving Dry-Well Calibrations

In practice, many customers use a dry-well as both a heat source and a reference thermometer. In other words, they put their thermometer or sensor to be tested in the well and compare its reading to the temperature on the display of the dry-well as shown in figure 1. The dry-well displays both the temperature the user set and the actual temperature measured by the dry-well’s own control sensor. If this is your practice, be aware of the following cautions.

First, several dry-well manufacturers don’t actually calibrate this display. When quoting the “accuracy” of their dry-well, some manufacturers actually give you the “potential” calibration accuracy if you use an adequate external thermometer to read the dry-well’s temperature during the calibration. You can only guess what the accuracy of the dry-well’s own display actually is.

Second, several manufacturers who do calibrate their displays and print specifications for display accuracy don’t include a traceable calibration report with the dry-well. You have to pay extra to get one. Both of these practices seem irresponsible to us. Fluke Calibration dry-wells all feature a calibrated display of the well’s temperature, and we include a traceable calibration report with every dry-well at no extra charge. If you’re buying a calibration instrument, why should you pay extra for the piece of paper that makes your instrument a valid calibration tool?

The first two cautions don’t apply if you buy a Flue Calibration dry-well. We design the electronics and sensor package for each dry-well to provide traceable accuracy that is reasonably adequate for many applications. However, your accuracy can be improved, even in a Fluke Calibration dry-well, if you use a more accurate reference thermometer during your calibrations. Some of our blocks feature multiple holes, and you can order two-hole inserts for our other models. This allows you to put your reference thermometer in close proximity to the sensor you’re testing as shown in figure 2.