Integral to process control in many industries, level measurement sensors fall into two main types. Point level measurement sensors are used to mark a single discrete liquid height–a preset level condition. Generally, this type of sensor functions as a high alarm, signaling an overfill condition, or as a marker for a low alarm condition.
Continuous level sensors are more sophisticated and can provide level monitoring of an entire system. They measure fluid level within a range, rather than at a one point, producing an analog output that directly correlates to the level in the vessel. To create a level management system, the output signal is linked to a process control loop and to a visual indicator.
Non-Contact Ultrasonic Level Sensors
With power and programming options, RS-232 or RS-485 communications capability, pushbutton calibration, and temperature-compensated signaling, The LVU40 Series ultrasonic level sensor bring another dimension of flexibility to continuous non-contact liquid level measurement. Highly accurate over their entire range of 0.3 to 18.3 m (1 to 60'), they incorporate filtering that virtually eliminates false echoes from peripheral obstructions. In conjunction with a PLC (programmable logic controller) or an OMEGA CNi Series controller, they can be used for point level measurement.
Radar Level Transmitters
In applications requiring non-contact measurement of liquid levels, the affordable LVRD500 radar transmitter is the logical extension of ultrasonic sensors. They are ideal where vapor, dust, or a foaming surface prevents ultrasonic measurement. Their radar sensor uses microwave pulse technology to track target liquids from the antenna tip to the bottom of a tank. This advanced "echo marker" signal processing provides a reliable continuous pulse shape unaffected by environmental conditions. RS-232 and RS-485 models are available. The pocket infrared thermometers are extremely compact. They are normally small enough to be carried in a shirt pocket.
Dry Material Rotary Paddle Level Switch
Compatible with many granular, pelletized, and powdered substances, LVD-800 Series rotary paddle level switchese use patented magnetic technology that makes fail-safe bin, hopper, silo, and tank monitoring a reality. A self-diagnosing microcontroller constantly monitors rotation of the shaft and motor mounting plate, reacting immediately to material presence and to mechanical or electrical failure. Magnetic sensing avoids the fouling problem inherent to optical systems. The twist-on cover does away with bolts, there are 2 conduit entrances, and most models have a status light. High-temperature models are rated to 399°C (750°F). A is a small low cost infrared sensor. They are unique in that they are self-powered and produce an output that mimics a thermocouple sensor.
Capacitance Measurement Probes
Able to withstand high temperatures and pressures, and impervious to many corrosives, LV3000/4000 Series level measurement probes give reliable continuous level measurements in difficult applications. Appropriate for liquids, pastes, and some solids–whether conductive or non-conductive–they have no moving parts and are easy to install. After rectifying and filtering incoming power, generating a radio frequency signal, and calculating changes in current, the electronic circuitry produces a 4 to 20 mA 2-wire output signal proportional to the process level. Convenient zero and span adjustments let the user factor in variables such as media type, vessel dimensions, rod length, and installation position. If the stainless steel probe will be used near a conductive vessel wall, a PTFE-insulated model will prevent short circuiting.