Physical level monitoring can refer to a wide range of different applications, and includes several options for sensing methods.
Some key questions to ask before selecting a level measurement sensor:
- Are you measuring a liquid or solid?
- Is point level or continuous measurement required?
- What level measurement range do you need?
- Is the measured material electrically conductive?
- Will the material coat or build up on surfaces?
- Does turbulence, foam, or vapor occur at the surface of the liquid?
- Will you need contact or non-contact level measurement?
- What are the application’s temperature and pressure ranges?
Thanks to the industrial standard inputs on the ezeio system, many sensors exist that are compatible with the ezeio.
Some technologies for level sensing are:
These types of sensors usually contain a magnetic float that moves up/down with the surface of a liquid, and the magnet actuates a switch. These sensors are mechanically very simple and low cost, and works well in many applications. They usually only output a on/off signal.
These sensors are usually mounted in the ceiling of a container, and send out a short burst of high frequency sound. The sensor measures the time it takes for the sound to bounce back to the sensor, and thus calculates the distance to the surface of the measured media.
Ultrasonic sensors can have very wide ranges, and are very practical since they do not have any direct contact with the measured fluid. Accuracy and consistency is usually also very good. The downside is that they can be expensive.
The output from the sensors is typically analog, and works well with the ezeio inputs.
Capacitive sensors work by measuring the changes in capacitance when more or less of the fluid is in proximity of the sensor. They are often designed as strips or bars that go down in the fluid measured, and will detect how far up the sensor the fluid reaches. Some capacitive sensors can be mounted on the outside of the tank, but that requires a non conducting container. Capacitive sensors also require that the fluid is conductive.
Conductive sensors can be very rugged and provide good accuracy and little drift over time. The output is typically analog, such as 0-10V or 4-20mA, and will match the inputs on the ezeio system perfectly.
Level can also be measured by monitoring the pressure at the bottom of the container. This can be useful for monitoring levels in very dirty fluids such as early stages in water treatment plants where the material contains a mix of solids. If the pressure sensor is integrated in the bottom of the container, there is no risk for things to get stuck or damage the sensors.