In-situ helium sensor based on temperature distribution change for hard disk drives
Publication Date: 2014-Jul-17
The IP.com Prior Art Database
Disclosed is a device which can sense the concentration of the helium gas in the hermetically sealed hard disk drives. The thermal diffusivity of helium gas changes with the concentration of it. By sensing the temperature distribution around the reading and writing head of hard disk drive, this device can measure the helium gas concentration
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This invention is about the methods and device which can measure the helium concentration of the hermetically sealed hard disk drives.
The thermal diffusivity of gas is defined as the ratio of heat conductivity to the product of density and the specific heat capacity. This thermal diffusivity explain how well the gas can transports the thermal energy when it is under flowing region. The helium's thermal diffusivity increases exponentially with its concentration. (See Figure 1)
Figure 1 Thermal diffusivity changes with the helium concentration. (=fraction)
Figure 2 shows the schematic and the working principle of the helium sensing device. The figure showed the front section of the slider unit of the hard disk drives.
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Figure 2 The schematic and the working principle of helium sensing devices. The TFC heater will generate the temperature distribution and two temperature sensor (thermistor) will measure it. Note that the temperature distribution changes when helium concentration decreases.
There are three main components which enable to measure the helium concentration. The first one is the Thermal flying height (TFC) heater. By applying electrical current in the TFC heater, TFC heater generates temperature distribution around the front section of the slider unit. And there is a flow which was generated by disk rotation under the slider, and this flow will transport the thermal energy and it will also generate the temperature distribution around the TFC heater. The other main components of this invention are the thermistors which is located around the reading and writing head. These thermistors measure the temperature distribution.
If the helium concentration decreases, the flow's trans...