EKO INSTRUMENTS CO., LTD. VIP Checker HC-121 Instruction Manual V2
Pg. 31
7. Measurement Principle
The principle of this measurement is by placing a sensor on a flat surface of a VIP sample, and run a fixed amount
of electric current to generate heat.
The heat generated below the sensor flows to VIP side. The heat flows to VIP side smoothly when the degree of
vacuum is low, the heat generated surface temperature decreases; on the other hand, when the degree of vacuum
is high, the thermal insulation performance increases, and the heat generating surface temperature increases.
The sensor is measuring the temperature difference between the VIP sample surface and the top part of thermal
resistance material inside the sensor after the heat generation. If the performance of VIP is maintained, its
surface temperature increases and the temperature differences inside the sensor become larger. If the
performance is low, the surface temperature decreases and the temperature difference inside the sensor becomes
less. HC-120 measures these temperature differences by thermocouple.
The relationships between the temperature differences and the thermal conductivity vary significantly by the
condition of all sorts of parameters, such as the VIP material, surfacing material, thickness, surface area,
temperature and humidity. From above reason, HC-120 is not a device to measure just the thermal conductivity,
but it is a device to evaluate VIPs, by using 3 types of VIP samples that are same type and shape with already
known 3 different thermal conductivities, which are measured under same measurement condition; from the output
values calculated in the preliminary calibration and the thermal conductivity calibration curve, estimate the thermal
conductivity based on the same type of VIP sensor then determine the threshold for the evaluation of the VIPs.
Therefore, when the VIP material changes, thermal conductivity of 3 types of VIP must be accurately measured by
using AUTO HC-074 and so on, and VIP samples to be used for calibration must be prepared. In addition to
preparing new VIP samples, the sensors must be recalibrated as well. The output value will vary even if the
sensor itself or channels are replaced; thus it is important to start with preparing calibration VIP samples that are
OK, n-NG, and NG upon quality control.
