Calorimeters, in broad terms can be ISOTHERMAL or ADIABATIC. These two methods refer to the accounting of the losses occurred during the measuring cycle.

In a simple form a calorimeter has a vessel which gets warm during the sample combustion and the temperature of the vessel is measured. Surrounding the vessel is an apparatus (enclosure), which can have many functions. Its main function is to either minimize or eliminate any heat loss or gain to the vessel so that the vessel temperature is a true reflection of the burned sample and not depending on changes in the air temperature, drafts and what other influences there are.

The isothermal method required that the enclosure has stable/constant temperature during the determination. Then the effect of the enclosure on the vessel can be measured and the temperature loss/gain can be calculated and compensated for in the result. The process is very slow.

The adiabatic method uses the physical rule that the vessel temperature cannot be influenced by the enclosure when the enclosure has the same temperature as the vessel. Therefore the enclosure is heated (and cooled) to follow the vessel temperature. The process is very complicated but reasonably fast.

It uses both the Isothermal and Adiabatic method, hence the term ISOBATIC. We invented the term to explain that the unit works in both methods. The method can change during the ignition phase. The actual method depends on the operating parameters. We have had good results with an isothermal initial period (before firing) and an adiabatic method after firing. This is achieved by having a low mass enclosure, which can be heated and cooled to any temperature. The CAL3K is the fastest and most accurate when the enclosure follows the vessel temperature (adiabatic) but remains below the vessel temperature (isothermal), because the heat losses don't have to be measured anymore. The losses are predictable, and are eliminated during calibration.

So, there it is: an ISOBATIC calorimeter, employing both the isothermal and the adiabatic method to obtain fast and precise results. The speed of the determination (Time from closing to open the lid) is important to some users. The ISOBATIC is the fastest method. The other modes are include for historical reasons.

1. ISOBATIC (sometimes called DYNAMIC)
2. ADIABATIC
3. ISOTHERMAL
4. EXPERIMENTAL