Level Measuring Devices

Level Measurement

Level measurement is the detection or measurement of the level of a liquid or other solid liquid. Two general types of measurement are direct measurement and indirect measurement. Direct level measurement, also known as mechanical level measurement, and direct level measurement, which measures the height of a liquid or other liquid fluid, and dip sticks and lead lines, sight glasses, chains, and float gauges are commonly used instruments. Indirect level measurement is also known as approximate or approximate method and basically this type of level measurement is level measured with a remote location. And commonly used instruments for indirect level measurement are sonar level measurement, ultrasonic level measurement, pressure gauge, pure mechanism, differential pressure meter, displacement type level measurement. 

Introduction to level measurement

A level measurement is the linear distance between the top surface of a liquid or solid and a predetermined reference point, such as a tank. Many types of level measurement instruments are used in industrial processes such as level sensors, level switches, level transmitters.

Level sensors

Level sensors are level indicators that measure liquid or solid levels in your process. Level measurement method is used in process automation.

Level switches

Level switches are sensors that trigger action via an electrical signal at a specific liquid, powder or bulk level.

level transmitter

Level transmitters are sensors with electrical signals that transmit level measurements of liquids, powders, or solids to a remote recording location.

Level Measurement Method

Level is the depth or height of a liquid or solid above a reference point. Level Measurement work according to three main different principles such as liquid surface position (height), pressure head, weight of material. Level measurement is divided into two measuring methods first direct method and second indirect method.

Direct Level Measurement 

Direct level measurement method is also known as mechanical method. Direct level measurement is straightforward and simple. It uses a direct measurement of distance (usually height) from a reference point. Direct level measurement is not readily adopted for signal transmission techniques for remote indication or control. Direct level measurement methods are simple and reliable.

Direct level measurement types

1. Dip-sticks and lead lines

2. Weighted gauge tape

3.Sight glass

4. Float and chain gauge

Indirect Level Measurement 

Indirect methods of level measurement are also known as approximate methods. The indirect method of level measurement relies on materials having physical properties that can be measured and related to the level. The indirect method of measurement uses the changing position of the liquid surface to determine the level with respect to a datum line. It can be used for low and high levels where direct method instruments are used such as hydro static pressure method, displacement instruments, capacitance level instrumentation, radiation-based level gauges. Several physical and electrical properties have been used for this purpose and are suitable for generating proportional output signals for remote transmission. This method uses very modern technology for its measurement.

Indirect level measurements include buoyancy, hydrostatic head, sonar or ultrasonic, microwave, radiation, conductance, capacitance, radiation, resistance, micro-impulse and weight.

bounce

The force produced by a body submerged in water is equal to the weight of the liquid it displaces.

Hydrostatic head

 The force or weight produced by the height of a liquid.

sonar or ultrasonic

The material to be measured reflects or affects in a detectable manner high frequency sound signals generated in a suitable location near the material being measured.

Microwave

Similar to ultrasonic but uses microwaves instead of ultrasonic beams.

conductance

At desired points of level detection, the material to be measured conducts (or stops conducting) electricity between two fixed probe positions or between the probe and the vessel wall.

Capacitance

The material to be measured acts as a variable dielectric between two fixed capacitor plates. In reality, there are two materials that make up the dielectric that is to be measured and the vapor space on it. The total dielectric value changes as the amount of one material increases and the other decreases.

radiation

The measured material absorbs the radiant energy. Like the capacitance method, the vapor space above the measured material also has absorptive characteristics, but the difference in absorbance between the two is so large that the measurement can be very accurately related to the measured material.

Weight

The force due to weight can be closely related to level when its density is constant. However, variable concentration factors or temperature variations pose difficulties.

Resistance

The pressure of the measured material compresses the two narrowly separated conductors together, reducing the overall circuit resistance proportionally.

Micro-impulse

Time-of-flight electrical pulses are emitted and travel at a frequency directly proportional to the liquid level.

Level measurement sensor

Basically level measurement is used to sensor to measure the level of liquid or other liquid and common level sensor is divided into two types. The first level measurement sensor type is point level measurement and the second level measurement sensor type is continuous level measurement

Point level measurement sensors used are capacitance sensors, optical sensors, conductivity sensors, vibrating sensors, float switches and continuous level measurement sensors are ultrasonic sensors and radar sensors.

Level Measurement Units

Units of level are millimeter (mm), centimeter (cm), meter (m), foot (ft), inch (inch).

Conversions between units

cm to inches = multiply cm by 0.394 (1 in ≅ 2.54 cm )

Inches to cm = inches divided by 0.394 (1 cm ≅ 0.394 inches)

Meters to feet = multiply m by 3.28 (1 foot ≅ 0.3048 meters)

Feet to Meters = Feet divided by 3.28 (1 meter ≅ 3.28 feet)