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 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 number of reed contacts, with respect to the measuring range. They are combined to form a measuring chain. The contacts respond to the magnetic field of the float, which moves within the guide tube good liquid level.
Accuracy depends on the distance between the contacts
The accuracy of the energy-free level monitoring depends, in turn, on the distance between the 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. This is because there are ? Trusting ? at both ends of the tube, i.e. sections that the float will not detect due to design constraints (see graphic).
The graph shows the way 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 isn’t a must
The measuring range of a level sensor therefore lies between the two dead bands specified in the data sheet. In this range, it is usually freely defined. However, it is by no means essential to utilise the maximum possible measuring range in every applications. The exact adaptation of the number of contacts to the measuring task also has an economic advantage: The reed chain is probably the priciest components in a level sensor.
Example ? Dry run monitoring
For dry run monitoring within 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, top of the measuring point of the application (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 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 beginning with the sealing face. In Admit , the guide tube could 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 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 following video: