Reed level sensor: Defining the measuring range flexibly

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. This short article describes what should be taken into account.
With a reed-chain level sensor, the guide tube contains a defined amount of reed contacts, with respect to 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 good 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: small 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 can’t be stretched across the entire amount of the guide tube. Endorsed is because you can find ?dead bands? at both ends of the tube, i.e. sections that the float will 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 range of an even sensor therefore lies between the two dead bands specified in the data sheet. Within this range, it could be freely defined. However, it really is by no means necessary to utilise the maximum possible measuring range in every applications. The precise adaptation of the number of contacts to the measuring task also has an economic advantage: The reed chain is probably the priciest components in an even sensor.
Example ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for example, only the lower area of the guide tube is necessary for the measurement. In cases like this, the upper measuring point of the application (100 % mark) is defined correspondingly low. It marks the length to the sealing face of the procedure connection. The measuring range is thus defined by the following 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 determined starting from the sealing face. In this instance, 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. In case you have any questions, your contact will gladly help you.
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