Bypass level gauges form an integral part of the pressure vessel.
Principle of operation
A stand pipe is attached to the side of a tank or a vessel across two process connections. With this direct connection, the filling level in the standpipe corresponds exactly to the level within the vessel (communicating pipes). A cylindrical float inside the bypass pipe has a built-in magnetic system. The magnetic field produced corresponds exactly to the level of the fluid in the standpipe. This magnetic field passes through the walls of the standpipe tube and is detected by indicator, recording, and switchgear elements attached on the outside.
Magnetic level gauges can also display the filling level visually. Small plastic or aluminium rollers with inlaid bar magnets are held in an aluminium or stainless steel profile bar. Depending on the level of filling in the stand pipe, these rollers turn from white to red as the level rises and from red to white as the level drops. The level inside the vessel can thus be displayed continually without requiring any outside power source.
The magnetic field in the cylindrical float acts through the wall on very small reed contacts that continually adjust the voltage from a resistive measurement chain. This voltage is proportional to the filling level (a 3-conductor potentiometer circuit). The resolution of the reed contacts is produced with spacing of 5, 10, and 15 mm.
Solenoid switches are used as limits for various filling levels. The permanent magnet in the cylindrical float activates a zero-potential bistable reed contact, which sends out a binary signal that can be used as a Full/Empty, pump On/Off, or valve Open/Close signal.
Technical advantages
* Simple, robust design.
* Pressure-tight separation between the measurement and display chambers.
* Detection and indication of the filling levels of aggressive, combustible, poisonous, hot, turbulent, and severely contaminated mediums.
* Operation of the level gauge without requiring an auxiliary power source.
* Models available for pressures ranging from vacuum to 400 bar.
* Models available for temperatures from -160 to 400°C.
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