A float-based level sensor with a reed chain is 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 needs to be taken into account.
With a reed-chain level sensor, the guide tube includes a defined amount of reed contacts, depending on measuring range. They are combined to form a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube good liquid level.
pressure gauge 10 bar depends on the length between the contacts
The accuracy of this energy-free level monitoring depends, subsequently, 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 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. pressure gauge 10 bar because there are ? ไดอะแฟรม ซีล ? at both ends of the tube, i.e. sections that the float does 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 selection of a level sensor therefore lies between the two dead bands specified in the info sheet. Within this range, it might be freely defined. However, it really 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 offers an economic advantage: The reed chain is probably the priciest components in a level 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 needed for the measurement. In cases like this, 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 process connection. The measuring range is thus defined by the next 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 beginning with the sealing face. In this case, the guide tube could be adapted to the length of the measuring range.
Note
More info on the RLT series level sensors are available on the WIKA website. Should 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 utilizing a reed chain in the following video: