No, using a reed level sensor a magnet is mounted in a float that is physically isolated from a reed switch that is usually mounted to a PCB in an isolated area, usually in the sensor stem.
Essentially a reed switch is required to sense the position of a magnet. The magnet is usually mounted to a float mechanism that moves with the changing level of a fluid.
Reed level sensors use reed switches as their switch sensing mechanism. In the off state there is no physical contact, so no current flows for as long as the contacts are open, which can be weeks, months, or years. When the contacts close they will switch on the appropriate circuitry carrying out the switching function.
Literally 100s of sensing points are possible. Reed switches can be mounted as close together as possible and can be mounted on long printed circuit boards that can be several meters long.
How many floats can be mounted on a stem for several trip points?
Standex Electronics has developed the LS04 series plastic level sensors with up to six floats on one stem. The stainless steel LS05 series can be as long as 2000mm and have any number of floats spaced at a minimum of 1.5″ apart. Standex Electronics engineers are always available for special design configurations
The reed level sensors are used in factory liquid level sensing, water seal float, oil level for transformers, air leak valve for waterworks, boiler control, auto-drain for pneumatic filter, lubricating units, generators, gasoline fuel dispensers, and more.
NBR (nitrile butadiene rubber) absorbs the least amount of liquid when immersed in oil, gasoline, alcohol, toluene, and benzene. It absorbs less them 0.5% of the fluid minimizing any float level inaccuracies.
Reed level sensors can be mounted vertically from the top or bottom of a vessel containing the liquid. Also, the sensors can be mounted on the side of the vessel as well. All the sensors can be mounted with their hardware either internal or external.
You can measure two different liquids particularly when they have different specific gravities. For example oil and water are two such liquids. If the liquids are sitting together only one stem is needed. The two floats having the proper float requirements (specific gravities), will ride up and down for the given liquid. Separate reed switches for each liquid within the stem, will supply the proper actuation.
NBR is a form of plastic material and stands for nitrile butadiene rubber. Standex Electronics uses it as a float material. It is excellent in its resistance to oil and fuel and withstands high temperatures very well.
The reed level sensors come in all different packages, but each sensor includes a housing that incorporates the reed switch and any circuitry along with wires to make the electrical connections to an external circuit. Also included is a float that contains a permanent magnet. The float can be part of the housing where it would ride up and down along the extension or stem of the housing. Floats can also be completely separate from the housing giving complete versatility to the sensor. When the float is in proximity to the reed switch, the contacts will sense the magnetic force closing the contacts.
Generally each technology has its pros and cons:
- Mechanical sensors are the least expensive but their subject to environmental conditions and generally fail earlier than the other technologies.
- Inductive sensors sense changes in inductance and capacitance to determine a given level. These are probably the most expensive.
- Hall and electronic sensors do a good job, but both need extra circuitry. So the initial investment of the sensor needs to be evaluated in conjunction with the other circuitry to determine the total cost. Also they draw power continuously, and they can be sensitive to some environmental extremes.
- The reed sensor requires no extra circuitry and uses no power in its off state. The designs are very flexible and because the reed switch is hermetically sealed they can be used in almost any harsh environment.
There are several technologies competing in the liquid level sensing market: primarily they are mechanical sensors, hall sensors, inductive sensors, and electronic sensors.
A liquid level sensor basically senses changes in the level of a fluid. It can be used to sense low level or high level points, and of course any point in between.