A float-based level sensor with a reed chain is really a widely used and comparatively economical solution for continuous level measurement in vessels. Users can define its measuring range flexibly within a given range. Piranha describes what has to be taken into account.
With Stable -chain level sensor, the guide tube includes a defined amount of reed contacts, based on the measuring range. They are combined to create a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube based on the liquid level.
Accuracy depends on the length between the contacts
The accuracy of the energy-free level monitoring depends, subsequently, on the distance between your 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 across the entire length of the guide tube. This is because there are ?dead bands? at both ends of the tube, i.e. sections that the float will not detect because of 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).
Freedom measuring range is not a must
The measuring range of a level sensor therefore lies between the two dead bands specified in the info sheet. Within this range, it might be freely defined. However, it really is by no means essential to utilise the utmost possible measuring range in all applications. The exact adaptation of the amount of contacts to the measuring task also has an economic advantage: The reed chain is one of the most expensive components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring within an oil tank of a compressor, for instance, only the lower portion of the guide tube is needed for the measurement. In cases like this, top of the measuring point of the application form (100 % mark) is set correspondingly low. It marks the distance to the sealing face of the procedure connection. The measuring range is thus defined by the next equation:
Measuring range length M = guide tube length L ? dead band T ? 100 % mark X
Consequently, the measuring range for detecting a maximum level is set starting from 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 can be found on the WIKA website. When you have any questions, your contact will gladly help you.
Also read our articles
Level sensors ? the agony of preference
What do dead bands mean with a float switch?
You can also find out more about float-based level measurement using a reed chain in the following video: