TABLE OF CONTENTS There are numerous ways to measure level that require differing technologies and to encompass all the various units of measurement.
Ultrasonic, transit time
Pulse echo
Pulse radar
Pressure, hydrostatic
Weight, strain gauge
Conductivity
Capacitive.
For continuous measurement, the level is detected and converted into a signal that is proportional to the level. Microprocessor-based devices can indicate level or volume.
Different techniques also have different requirements. For example, when detecting the level from the top of a tank, the shape of the tank is required to deduce volume.
When using hydrostatic means, which detects the pressure from the bottom of the tank, the density is to be known and remains constant. Level sensing is a simpler concept than most other process variables and allows a very simple form of control. The sensors can be roughly grouped into categories according to the primary level sensing principle involved.
The signals produced by these means must then be converted into a signal suitable for process control applications, such as an electrical, pneumatic or digital signal.
The following are outlines of the more important considerations that need to be considered when installing either atmospheric or pressurized vessels.
Most instruments involved with level detection can be easily removed from the vessel. Top mounting of the sensing device also eliminates the possibility of process fluid entering the transducer or sensor housing should be the nozzle or probe corrode or breaks off. Many level measurement devices have the added advantage...
