Reed level sensor: Defining the measuring range flexibly

A float-based level sensor with a reed chain is really a trusted and comparatively economical solution for continuous level measurement in vessels. Users can define its measuring range flexibly inside a given range. This article describes what must be taken into account.
With a reed-chain level sensor, the guide tube contains a defined amount of reed contacts, depending on the measuring range. These are combined to form a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube in line with the liquid level.
Accuracy depends on the length between the contacts
The accuracy of this energy-free level monitoring depends, subsequently, on the distance between the individual contacts: the smaller it really is, the more accurate the measurement. Each level sensor in WIKA?s RLT series, for instance, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain cannot be stretched along the entire length of the guide tube. It is because you can find ?dead bands? at both ends of the tube, i.e. sections that the float does not detect due to design constraints (see graphic).
The graph shows how the maximum possible measuring range (M) with an air-handling series level sensor is defined: Guide tube length (L) minus dead band (T) and 100 % mark (X).
Maximum measuring range is not a must
The measuring selection of a level sensor therefore lies between your two dead bands specified in the info sheet. In this range, it can be freely defined. However, it really is by no means essential to utilise the utmost possible measuring range in all applications. The precise adaptation of the amount of contacts to the measuring task also has an economic advantage: The reed chain is among the most expensive components in an even sensor.
Example ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for instance, only the lower area of the guide tube is needed for the measurement. In this case, the upper measuring point of the application (100 % mark) is set correspondingly low. It marks the distance to the sealing face of the process connection. The measuring range is thus defined by the next equation:
Measuring range length M = guide tube length L ? dead band T ? เกจวัดแรงดันแก๊สหุงต้ม , the measuring range for detecting a maximum level is determined beginning with the sealing face. In cases like this, the guide tube can be adapted to along the measuring range.
Note
More info on the RLT series level sensors are available on the WIKA website. For those who have any questions, your contact will gladly assist you to.
Also read our articles
Level sensors ? the agony of choice
What do dead bands mean with a float switch?
You can also find out more about float-based level measurement utilizing a reed chain in the next video:

Leave a Comment