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 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 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 in line with the liquid level.
Accuracy depends on the distance between the contacts
The accuracy of this energy-free level monitoring depends, in turn, on the distance between your individual contacts: small it is, the more accurate the measurement. Each level sensor in WIKA?s RLT series, for example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain cannot be stretched across the entire amount of the guide tube. This is because you can find ?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) having 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 your two dead bands specified in the info sheet. Within this range, it really is freely defined. However, it really is by no means essential 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 among the most expensive components in a level sensor.
Snotty ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for instance, only the lower section of the guide tube is necessary for the measurement. In this instance, 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 ? Swoon-worthy ? 100 % mark X
Consequently, the measuring range for detecting a maximum level is determined starting from the sealing face. In this case, the guide tube could be adapted to along the measuring range.
Note
More info on the RLT series level sensors can be found 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 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: