4.1 How Intelligent 2 Probe Control functions
Intelligent 2 Probe Control takes advantage of the fact that increasing the temperature differential between two objects increases the rate of heat transfer between them. For instance, if a thick and heavy object is to be heated from 0/ to 100/, and the object is placed in a temperature chamber with a 100/ internal air stream temperature, the temperature of the object will rise quickly at first because of the large differential between the temperature of the chamber air stream and the object.
However, as the object continues to absorb heat, the differential decreases and the rate of heat transfer decreases. The closer the object’s temperature approaches the air stream temperature, the more slowly the object absorbs heat. To maintain the thermal transfer efficiency that existed early in the warming process (when the differential was, for example, 80/), the air stream would have to continually get warmer as the object heated. When the object was 20/, the air would have to be 100/, when the object was 50/, the air would have to be 130/, when the object was 80/, the air would have to be 160/, etc. Heating efficiency can be substantially improved by this method.
However, because our object is thick and heavy, there likely is a large temperature differential between the surface temperature of the object and the core temperature that we are measuring. Even though the object’s core is only 80/ at some point in this process, the surface temperature, exposed to 160/ air, may well be much higher. In fact, if the object is a poor thermal conductor, the surface temperature may approach the air temperature... in this example, 160/.
While we would like to have our object’s core temperature increase as quickly as possible, inducing a surface temperature that is 60/ over the setpoint may be more than the object can tolerate. If we knew, however, that the object’s surface could tolerate 130/, then we could use an air stream temperature of 130/ - but no more - to speed the transfer of heat into the object.
When the object’s core temperature started to approach the setpoint, we could reduce the amount of over heating of the air and object surface. The closer the core temperature got to the setpoint, the less overheating would be applied.
Eventually, just as the core temperature reached the setpoint, the amount of overheating would be zero. The ramp rate of the core of the object would have been maximized without exposing any of the object to temperatures exceeding it’s tolerance.
There is one more consideration. You may want to achieve an object core temperature as quickly as possible to improve production testing efficiency, but you may want to not apply thermal differentials that will “shock” the object you are testing. In fact, the object may have more tolerance for differentials when hot
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