Littlefield Technology

4.2 Measuring System
4.2.1 Sensors

Two types of measuring sensors, namely, thermocouples and pressure gauge are used to measure temperature and pressure respectively. To measure wall temperature, two thermocouples are placed on the top surface of copper heater in different point. In objective to determine temperature distribution along the heater, three thermocouples are equally attached along the heater. Another three thermocouples are placed on its surface in order to determine temperature distribution along the insulation. The arrangement of all thermocouples in the heater base is shown on Fig. 4.6. Liquid and vapour temperature of coolant are measured by two thermocouples positioned inside the chamber. The response thermocouple is critical in the temperature measurement. K-types thermocouples which posses fast response capability with an uncertainty of ±0.4% for the full range are used in the experiments. All thermocouples are to be calibrated before the experiments.

Fig. 4.6 Thermocouples arrangement on the heater and insulation

Saturation temperature of working fluid is depended on operation pressure. In order to measure the pressure inside the chamber, a pressure gauge was placed on the cooling top section as shown in Fig. 4.5. The pressure level was always recorded for all power input in the experiments. Correlation provided by coolant manufacturer is used to determine the saturation temperature of the coolant. The table of saturation temperature of HFE-7000 and FC-72 for various pressures are provided in the APPENDIX.

4.2.2 Data Acquisition System
The data measured by thermocouples are monitored and acquired by a Data Acquisition (DAQ) apparatus. Yokogawa MW 100 Data acquisition Unit was used to perform data acquisition system. The unit consists of a main module equipped with an ethernet port, I/O modules for input and output of signals, and a base plate to which the first two items are mounted. The main modules come with HTTP server...