Level Control and Measurement

Measure and monitor fluid levels

Measuring and monitoring fluid levels accurately and precisely requires choosing the correct methodology for the target vessel. Generally, there are six methods for measuring and monitoring fluid levels, namely:

• Continuous float level transmitters
• Differential pressure transmitters
• Radar level transmitters
• Ultrasonic level transmitter
• Load cells
• Radio Frequency

Continuous Float Level Transmitters

These level monitors operate using a float suspended in the fluid from a rod, something of a dip-stick, which sends a vibration up the rod to a sensor.

Differential pressure transmitters

Differential pressure transmitters can be used to determine fluid levels by determining the difference in head pressure between the low-pressure port and the high-pressure port in its usual configuration.

Radar Level Transmitters

Radar is a non-contact method that entails bouncing an electromagnetic pulse off a fluid surface and measuring the time required to return to the sensor.

Ultrasonic level transmitter

Like radar, Ultrasonic sensors are less sensitive to medium characteristics and vessel construction.

Load cells

A load cell is a transducer technique that measures weight, a mechanical force, or a load and creates an output signal which relays data to be extrapolated into a fluid level.

Radio Frequency

RF technology uses the electrical characteristics of capacitors in a vessel to map the contours of the surface area.

Fluid level sensors

Fluid level sensors, or liquid level sensors, are used to monitor and regulate levels of a particular free-flowing substance within a space. These substances are usually liquid; however, liquid level sensors can also be used to monitor solids, such as powders. There are many different types of liquid level sensors, and they have several uses.

Basic fluid level sensors can identify the point at which a liquid falls below a minimum or rises above a maximum level. Many liquid level sensors can detail the specific amount of liquid in a container relative to the minimum/maximum levels to continuously measure volume.

Fluid level sensors are the sensors used for detecting liquid levels or interfaces between liquids such as water and oil or solids. These sensors can also be defined as transducers or integrated systems with instrumentation and control capabilities. This type of liquid level sensor is one of the most critical sensors and plays an essential role in various industrial and consumer applications.

Level measurement technologies

The most straightforward industrial level measurement device is the sight glass, a manual approach to measurement, not without its limitations. The material used for its transparency can suffer failure, with ensuing environmental insult, hazardous conditions for personnel, and fire and explosion. Seals are prone to leak, obscuring the visible level, and more advanced technologies are rapidly replacing them.

Other level-detection devices include those based on specific gravity, the physical property most commonly used to sense the level surface. A simple float with a specific gravity between the process fluid and the headspace vapor will float at the surface, accurately following its characteristics. Hydrostatic head measurements have also been widely used to infer levels.

When more complex physical principles are involved, emerging technologies often use high-end computers to perform the calculations. This requires sending data from the sensor to the control or monitoring system. Practical transducer output signal formats for computer automation are current loops, analog voltages, and digital signals. Analog voltages are simple to set up and deal with but may have severe noise and interference issues.

Types of industrial level sensors

Point level measurement

Capacitance level sensors

The capacitance level sensors are operated by using a probe for checking changes in the level. These level changes are converted into analog signals. Most commonly, the examinations consist of conducting wire by PTFE insulation.

Optical Level Sensors

The optical sensors work based on the changes of transmission in infrared light emitted from an IR LED. By using a high-energy IR diode and pulse modulation methods, the interference from the produced light can be reduced.

Continuous Level Measurement Sensors

Industrial ultrasonic level sensors

Industrial ultrasonic sensors are also used to detect the levels of sticky liquid substances and bulkiness materials. They work by emitting and receiving ultrasonic waves at roughly 20 to 200 kHz.

Radar (Microwave) Sensors

The operation of radar or microwave sensors is similar to ultrasonic. But, the pulses travel at the speed of light. The repeatability and reliability can be exaggerated, but this time by the dielectric constant of the fluid.