Head Devices

A commonly used basis for classification of level devices is as follows float-ac tuated, displacer, and head devices, and a miscellaneous group that depends mainly on fluid characteristics. 

Head Devices A variety of devices utilize hydrostatic head as a measure of level. As in the case of displacer devices, accurate level measurement by hydrostatic head requires an accurate knowledge of the densities of both heavier-phase and lighter-phase fluids. The majority of this class of systems utilize standard-pressure and differential-pressure measuring devices. 

Pyrometer Vortex-shedding Diaphragm Head devices Raman spectroscopy... 

Fig. 4.5. Mariotte flask. A constant pressure head device.

Table 2 Guidelines for the use of HIER buffers and heading devices... 

Matsuyama, H., Eguchi, H. Karamon, H. (1990). The high-resistive soft magnetic amorphous films consisting of cobalt, iron, boron, silicon and oxygen, utilized for video head devices. Journal of Applied Physics, 67, 5123-5. 

In a ram- or plunger-type machine, the extruder feeds the material to an accumulator/head device. The plunger pushes the material rapidly through the head-die assembly once the desired volume has accumulated. The transfer of material does not need to occur via a blowing station in the mould clamp mechanism. The part is blown, cooled and removed from the mould, and the next parison is only extruded after the part has been removed. 

Figure 21.5fbl shows a positive displacement pump increasing the pressure of a process stream The positive displacement pump can be considered to be a constant-flow, variable-head device that is, it will deliver the same flowrate of fluid at a wide range of discharge pressures. Thus we may write ... 

Pyrometer Ultrasonic Strain gauges Head devices Ultraviolet (UV) spectroscopy... 

IMO, Resolution MSC.116(73) Performance Standards for Marine Tr smitting Heading Devices (THDs), Dezember 2000. 

Pressure/head devices such as the DP cell are the most popular of all level measurement devices. The DP cell can often be used where manometers are impracticable and floats would cause problems. The DP cell requires a constant product density for accurate measurement of level, or a way of compensating for density fluctuations. Figure 2.8 demonstrates a typical set-up for level measurement using a Rosemoimt Model 3095 level controller, which is essentially a combined DP cell and proportional controller. 

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