In all thermal systems there are four major parts:
- The Work Load: This is the material to be heated.
- The Heat Source: Either electrical resistance or fuel fired heat.
- The Heat Transfer Medium: The solid, liquid, or gas that transfers the heat energy to the load.
- The Controlling Device: The sensing and controlling devices that control the amount of heating and maintain a specific temperature for the load.
Of the four major parts of a closed loop system, the sensor’s location will play a major role, provided the other elements of the system have been properly selected. Placement of the sensor in relationship to the work load and heat source can compensate for various types of energy demands from the work load.
Sensor placement can limit the effects of thermal lags in the heat transfer process. The controller can only respond to the temperature changes it “sees” through feedback from the sensor location. Thus, sensor placement “in the sweet spot” will influence the ability of the controller to regulate temperature about a desired set point.
Sensor placement can limit the effects of thermal lags in the heat transfer process. The controller can only respond to the temperature changes it “sees” through feedback from the sensor location. Thus, sensor placement “in the sweet spot” will influence the ability of the controller to regulate temperature about a desired set point.
Sensor In a Static System
We call a system “static” when there is slow thermal response from the heat source, slow heat transfer, and minimal changes in the work load. With the sensor placed at or near the heat source, it can quickly sense temperature changes and maintain tight control.
Sensor In a Dynamic System
We call a system “dynamic” when there is rapid thermal response from the heat source, rapid heat transfer and frequent changes in the work load. When the system is dynamic, placing the sensor closer to the work load will enable the sensor to “see” the load temperature change faster and allow the controller to take the appropriate output action more quickly.
We recommend that the electronic controller selected for this situation include the PID features (anticipation and offset ability) to compensate for these conditions. With the sensor at or near the workload, it can quickly sense temperature rises and falls.
We recommend that the electronic controller selected for this situation include the PID features (anticipation and offset ability) to compensate for these conditions. With the sensor at or near the workload, it can quickly sense temperature rises and falls.
Sensor Placement Examples In Solids
A conduction system might consist of the heat source in direct contact with the heat transfer medium which in turn heats the load.
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