[1] A level sensor is a device detecting the liquids level (often heights) and other fluids and fluidized solids, including slurries, granular materials, and powders that exhibit an upper free surface. Substances that flow become essentially horizontal in their containers (or other physical boundaries) due to gravity whereas most bulk solids pile at an angle of repose to a peak.
[1] The measured substance can be in a container or in natural forms (e.g., rivers or lakes). The level measurement is either continuous (analog) or point (or even multipoint) (digital) values. Continuous level sensors measure level within a specified range and determine the exact amount of substance in a certain place, while point-level sensors only indicate whether the substance is above or below the sensing point. Generally the latter detect levels that are excessively high or low.
point level: detects if material reached a location (high/low) signal
multipoint level: extension of point level where many sensors are installed are installed at various height in same container
[D1] In instrumentation level refers to material height (liquid/solid) in container.
Flow is measured for:
to prevent tank overflow
to prevent empty tank condition
to protect tank electric heaters
to control inventory (quantity remaining)
to provide enough material for batch processing. (e.g., flour for bread)
Level sensors are often categorized as contact (touches the liquid) and non-contact (does not touch), and further divided by whether they measure point (specific height) or continuous (exact level).
A float switch is a point (digital) level sensor using a buoyant float that moves up and down with the liquid, triggering a magnetic or mechanical switch at some height. It's used in sump pump, toilet, or basic alarms.
[D1] Float switches often use reed switches and magnets. As the magnet nears the reed switch the switch closes. The section with the magnet floats in the liquid and rises/falls depending on position.
reed switch: electric switch operated by magnetic field, featuring thin metal reeds in sealed glass tube
[3] 2 Gems LS-7 plastic level float switches
A magnet float level switch uses buoyancy. Its float moves up/down as the liquid level changes.
Through magnetic triggering, the float has an embedded permanent magnet.
If the liquid level moves the float close to the stationary stem, the magnetic field forces the reed switch's internal electrical contacts to close (or open, depending on the configuration).
This completes/breaks an electrical circuit, sending an ON/OFF signal to a pump, alarm, or control system.
In the right diagram's magnetic level switch's 1/2 NPT thread allows the unit to be screwed horizontally into the side wall of a tank or vessel.
[D1] a magnetic float level switch (specifically a horizontal mount liquid level sensor).
[D1] The float's density must be less than the measured liquid.
A float switch's plastic container's buoyancy causes it to float. The volume's mass is less than that of the liquid it displaces.
A capacitive sensor can be either a point or continuous level sensor measuring the change in capacitance as the material (which has a different dielectric constant than air) covers its probe.
A hydrostatic (pressure) sensor is a continuous level sensor measuring the pressure exerted by the liquid column at the bottom of the tank. It's used in deep tanks, water wells, open or pressurized vessels.
A conductive (probe) sensor is a point level sensor using electric conductivity. If liquid touches 2 probes, it completes a circuit. It's used in water/acid/conductive liquid (not for oils/non-conductors).
An ultrasonic sensor can be either a contact, non-contact, or both (hybrid), thought most are non-contact, continuous level sensor. It sends sound waves down a probe (guided wave) and measures the reflection time. It's used in vaporous/turbulent environments where standard ultrasonics fail.
An displacer sensor is a continuous level sensor using Archimedes' principle; a weight displacer hanged in the liquid and the change in apparent weight is measured. It's used in interface level (oil/water separation) and high-pressure /temperature applications.
A ultrasonic sensor is a continuous level/distance sensor emitting sound pulses based on the echo return time. It's used in water treatment, chemical tanks, open channels.
A radar sensor is a continuous level sensor emitting microwave pulses (non-contact) or guided waves (contact), thus it can be either contact or not. It measures the flight time.
It has variants that are further known as pulse radar (the standards) and the FMCW radar, for high precisions.
A nucear radioisotope sensor is a continuous point level sensor using a radioactive source on 1 side of its tanka nd a detector on the other one. The measured material absorbs radiation, less radiation rises the leve. It's used in extreme conditions (very high tempreature/pressure), hazardous material or where no contact is possible).
A laser sensor is a continuous point level sensor that, alike radar sensors, uses a laser beam, but at very narrow angles. It's used in small tanks, vending machines, or medical devices.
Optical and mechanical sensors are level sensors using light to detect a something's presence, using light refraction.
A tuned fork (vibration) sensor is a point level sensor using a fork vibrating at a resonant frequency. If covered by material, the frequency changes, triggering its switch. It's used in powders, granulles, and liquids, good for solid detections.
A rotating papddle sensor is a point level sensor using a motor that spins a paddle. If material stop sthe paddle, the motor stalls, triggering a switch. It's used in bulk solids, powders, and granules.
[D1]
A sight glass sensor is a continuous visual level sensor. It's comprised of a clear glass/plastic tube connected to the tank side. It uses a visual verification to indicate something (often a tank)'s liquid level.
Dipstick is a method used by gas stations to check the fuel level in underground storage tanks.