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 article describes what needs to be taken into account.
With Bargain -chain level sensor, the guide tube contains a defined amount of reed contacts, with regards to the measuring range. These are combined to form a measuring chain. The contacts respond to the magnetic field of the float, which moves within the guide tube based on the liquid level.
Accuracy depends on the distance between the contacts
The accuracy of the energy-free level monitoring depends, subsequently, 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 example, enables measuring ranges with contact distances between 3 and 24 mm. However, a reed chain can’t be stretched along the entire amount of the guide tube. The reason being 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 the way 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 selection of a level sensor therefore lies between the two dead bands specified in the data sheet. In this range, it might be freely defined. However, it really is by no means essential to utilise the maximum 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 one of 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 needed for the measurement. In this instance, top of the measuring point of the application form (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 case, the guide tube can be adapted to the length of the measuring range.
Note
More info on the RLT series level sensors can be found on the WIKA website. Should 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?
There are also out more about float-based level measurement using a reed chain in the following video: