Reed level sensor: Defining the measuring range flexibly

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 inside a given range. This article describes what needs to be taken into account.
With Helplessness -chain level sensor, the guide tube includes 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 length between the contacts
The accuracy of the energy-free level monitoring depends, in turn, on the distance between the individual contacts: the smaller 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 can’t be stretched across 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 will not detect because of design constraints (see graphic).
Unlock 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 isn’t a must
The measuring range of a level sensor therefore lies between your two dead bands specified in the data sheet. In Horrifying , it could be freely defined. However, it really is by no means necessary 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 priciest components in an even sensor.
Example ? Dry run monitoring
For dry run monitoring in an oil tank of a compressor, for instance, only the lower part of the guide tube is necessary for the measurement. In this instance, top of the measuring point of the application form (100 % mark) is set 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 set starting from the sealing face. In cases like this, the guide tube can be adapted to along the measuring range.
Note
Further information 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 choice
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:

Leave a Comment