The sensors are embedded in the vessel walls. The electronics are located in the bottom of the vessel and are vacuum encapsulated to prevent any liquid or dust from affecting the temperature measurement. The temperature is measured with platinum sensors, which are near linear, and the readings are linearised to become absolute linear. This is a major advantage as the vessel can be fired at any temperature and remains perfectly calibrated. The temperature measuring range is 5 to 70 Celsius. A typical determination rises the vessel temperature by approximately 10C.

The temperature sensors are stable at a working resolution of 0.000001°C or 1 part per million. To put this into some kind of perspective: it is very little. The electronics in the vessel consume a constant of about 0.04Watts, which is automatically corrected for. Because the electronics work at the same temperature as the vessel the overall temperature (rise) accuracy is in the range of 10ppm (0.00001).

What does all this mean in real terms?

The theoretical electronic accuracy related to 26Kj/g is 0.0003Kj/g. Of course, this is not the accuracy you can expect on the final result, which is subject to moisture, sample preparation, sample consistency, weighing and operator procedure, and a lot of other influences. Basically, the CAL4K_4 vessel can be used for extremely accurate results, but is limited by its use.

The vessel tests itself every time it is inserted into the bomb well. The results are reported back to the calorimeter for storage and displaying. The vessel electronics are tested three times in the factory - after assembly, then after 24 hours oven burn-in, and then finally after packaging. All the times are recorded in the vessel memory together with such information as: Customer, Assigned Serial Number.