What are Level Sensors?

Level sensors are used to detect liquid or powder levels, or interfaces between liquids. These level measurements can be either continuous or point values represented with various output options. Continuous level sensors are devices that measure level within a specified range and give output of a continuous reading of level. Point level sensors devices mark a specific level, generally used as high alarm or switch.

Multiple point sensors can be integrated together to give a stepped version of continuous level. These level sensors can be either plain sensors with some sort of electrical output or else can be more sophisticated instruments that have displays and sometimes computer output options. The measuring range is probably the most important specification to examine when choosing a level sensor. Field adjustability is a nice feature to have for tuning the instrument after installation.

Depending on the needs of the application, level sensing devices can be mounted a few different ways. These sensors can be mounted on the top, bottom or side of the container holding the substance to be measured. Among the technologies for measuring level are air bubbler technology, capacitive or RF admittance, differential pressure, electrical conductivity or resistivity, mechanical or magnetic floats, optical units, pressure membrane, radar or microwave, radio frequency, rotation paddle, ultrasonic or sonic and vibration or tuning fork technology. Analog outputs level sensors can be current or voltage signals. Also possible is a pulse or frequency. Another option is to have an alarm output or a change in state of switches. Computer signal outputs that are possible are usually serial or parallel. Level sensors can have displays that are analog, digital or video displays. Control for the devices can be analog with switches, dials and potentiometers; digital with menus, keypads and buttons; or controlled by a computer.

What is a Flowmeter?

Flow measurement is the quantification of bulk fluid or gas movement. It can be measured in a variety of ways.

Volumetric flow rate is sometimes measured in "standard cubic centimeters per minute" (abbreviation sccm), a unit acceptable  for use with SI except that the additional information attached to the unit symbol. The SI standard would be m3/s (with any  appropriate prefix, with temperature and pressure specified). The term "standard" indicates that the given flow rate assumes  a standard temperature and pressure. Many other similar abbreviations are also in use, such as standard cubic feet per minute  or per second. Other units used include gallons (U.S. liquid or imperial) per minute, liters per second, bushels per minute,  and acre-feet per day.

Another method of flow measurement involves placing an object (called a shedder bar) in the path of the fluid. As the fluid  passes this bar, disturbances in the flow called vortices are created.

The vortices trail behind the cylinder in two rolls,  alternatively from the top or the bottom of the cylinder. This vortex trail is called the Von Kármán vortex street after von  Karman's 1912 mathematical description of the phenomenon. The speed at which these vortices are created is proportional to  the flow rate of the fluid. Inside the shedder bar is a piezoelectric crystal, which produces a small, but measurable,  voltage pulse every time a vortex is created. The frequency of this voltage pulse is also proportional to the fluid flow  rate, and is measured by the flowmeter electronics.

Modern innovations in the measurement of flow rate incorporate electronic devices that can correct for varying pressure and  temperature (i.e. density) conditions, non-linearities, and for the characteristics of the fluid.