Capacitive level gauge

Basic Information
definition
Capacitive level gauge is one of the electrical level detection methods, which directly converts the change in level into the change in capacitance, and then converts it into a unified standard electrical signal, which is transmitted to the real instrument for indication, recording, alarm or control.
working principle
The capacitance detection element of a capacitive level gauge operates based on the principle of cylindrical capacitors, which consist of two insulated coaxial cylindrical plates with inner and outer electrodes. When an electrolyte with a dielectric constant e is charged between the two cylinders, the capacitance between the cylinders is C=2 π eL/lnD/d, where L is the length of the overlapping part of the two cylinders; D is the diameter of the outer cylinder electrode; D is the diameter of the inner cylinder electrode; E is the dielectric constant of the intermediate medium. In actual measurement, D, d, and e are basically unchanged, so measuring C can determine the level of the liquid
2 Latest Applications
Introduction
Latest Applications of E H Capacitive Level Gauge
E H capacitive level gauge is a level measuring instrument made based on the relationship between output capacitance and liquid level. E H capacitance instrument is used for continuous or limit measurement of liquid level or solid material level. Suitable for industrial applications such as power, metallurgy, chemical, food, brewing, pharmaceuticals, sewage treatment, boiler steam drums, etc.
application
Latest Applications of E H Capacitive Level Gauge
Liquicap T FMI21 Range: 150... 2500 mm/0.5... 8.4 ft
Electrode type: rod type
Temperature range: -40... 100 ° C/-40... 212 ° F
Pressure resistance: -1... 10 bar/... 145 psi
Output signal: 4... 20 mA
Detailed information on the latest application of Liquicap T FMI21 in the E H capacitive level gauge
Liquicap M FMI51 Range: 100... 4.000 mm/0.3... 13 ft
Electrode type: rod type
Temperature range: -80... 200 ° C/-112... 392 ° F
Pressure resistance: -1... 100 bar/-14.5... 1450 psi
Output signal: 4... 20 mA/HART® , PFM
Details of Liquicap M FMI51
Liquicap M FMI52 Range: 420... 10.000 mm/1.4... 33 ft
Electrode type: rod type
Temperature range: -80... 200 ° C/-112... 392 ° F
Pressure resistance: -1... 100 bar/14.5... 1450 psi
Output signal: 4... 20 mA/HART® , PFM
Minicap FTC260 Range: 140 mm/5.5
Type: Integrated
Temperature range: -40... 120 ° C/-40... 248 ° F
Pressure resistance: -1... 25 bar/... 362.5 psi
Particle size: up to 30 mm

working principle
The capacitive level gauge consists of a capacitive level sensor and a circuit for detecting capacitance. The basic working principle is that the capacitive level sensor converts the level into a change in capacitance, and then uses the method of measuring capacitance to obtain the level value.
Capacitive level sensors operate based on the principle of cylindrical capacitors. Its structure is like two cylindrical metal conductors with a length of L and radii of R and r, separated by an insulating material. When the medium filled in the middle is a gas with a dielectric constant of ε 1, the capacitance of the two cylinders is:
C1=2 πε 1L/R (㏑ R/r) (1) If a part of the electrode is immersed in a liquid with a dielectric constant of ε 2 (non-conductive), there must be an increase in capacitance △ C (because ε 2>ε 1), at which point the capacitance between the two poles C=C1+△ C. If the electrode is immersed for a length of l, the capacitance increment is:
◎C = 2π(ε2 - ε1)i/(㏑R/r) (2)
When ε 2, ε 1, R, and r remain constant, the capacitance increment △ C is proportional to the length l of the electrode immersion, so measuring the capacitance increment value can determine the liquid level height.
If the measured medium is a conductive liquid, the electrode should be covered with an insulating material (such as polyethylene) as an intermediate medium, and the liquid and the outer cylinder together serve as the outer electrode. Assuming the dielectric constant of the intermediate medium is ε 3 and the electrode is submerged for a length of l, the capacitance of the capacitor at this time is:
C = 2pe3i/(㏑R/r) (3)
Among them, R and r are the outer radius of the insulation coating and the outer radius of the inner electrode, respectively. Since ε 3 is a constant, C is proportional to l.

The principle of capacitance. Equivalent to two electrodes, when the material rises and falls in the middle, the average dielectric constant will change, resulting in a change in capacitance. After calibration, you can check the change in capacitance. So this product is not very suitable for strongly conductive materials. The measurement principle of a capacitive level gauge is that a probe and a conductive liquid form a capacitor, where the metal core of the probe line is one pole of the capacitor, the conductive liquid is the other pole of the capacitor, and the middle is a highly stable polytetrafluoroethylene, that is, the insulating outer layer of the probe line serves as the medium between the two poles. As the liquid level changes, the area of the liquid surrounding the probe line changes, causing the relative area of the two poles that make up the capacitor to change, resulting in a change in capacitance. According to the formula for concentric cylindrical capacitors, the relationship between liquid level height and capacitance can be written.

How is the capacitance of a capacitive level gauge detected through a circuit?

The working principle is to detect capacity based on the dielectric constant.
There are two commonly used methods in practice
1. Multiple capacitive proximity switches are used for high and low point detection. When the material rises to the capacitive detection surface, the capacitive sensor outputs a switch signal.
2. Adopting a direct insertion type, this level gauge usually has a long stainless steel rod inserted into the container. When the level slowly rises or falls and the capacitance changes, the capacitive sensor can output an analog signal. When the set upper or lower limit is reached, an alarm signal is output, and this sensor can detect the position in real time.

What is the difference between level gauge, level gauge, liquid level gauge, and flow meter?

Level gauge: Static pressure level gauge. Ultrasonic level: capacitive level gauge
Level gauge: also known as level transmitter, level controller, level switch, level gauge, etc
Level gauge, magnetic float level gauge, internal floating dual chamber level gauge, input level gauge, static pressure input level transmitter
There are too many flow meters, vortex street electromagnetic orifice plates, V-cones, and so on
They all have one thing in common, which is to use some special sensors to convert the measured signals into standard signals of 4-20mA or 1-5V or pulse signals, current signals, etc., which are amplified and displayed by secondary instruments. Make people read.
The flowmeter measures gases, high-temperature steam, water and other media in pipelines, so its measurement requires instruments such as thermal resistance and pressure transformers to compensate for temperature and pressure more accurately. Therefore, it is a set of measurement components. At the same time, its measurement conditions are very complex. The selection itself needs to go through a series of calculations such as pipelines and on-site conditions in order to buy the type that suits oneself according to requirements. The unit of measurement for the measured flow rate can also be converted into calorific value, mass, cubic meter, etc
Why don't we use a weighing sensor to measure the increase or decrease of force in a container like you said. The simplest example is that if your container is filled with 5T of liquid or object, you need to use a weighing sensor to calculate its weight. Where do you install this sensor to measure? How to lift a 5T container during maintenance? A sensor like this is expensive. How to control costs? The most important thing now is industrial automatic control. If weight control is possible, no one can afford it, and containers are not just about measuring different media with different requirements.