Process Engineering Division – Instrumentation and Automation Technology Exchange Forum – Daily Question – Question dated 2020-01-16

Direct-reading level gauges, differential pressure level gauges, buoyancy-based level gauges, electromagnetic level gauges, nuclear radiation level gauges, acoustic property measuring instruments, optical level gauges.

Direct-reading； Differential pressure type ； Buoyant type ； Electromagnetic ； Nuclear radiation type ； Acoustic wave type ； Optical object imitation.

Direct-reading level gauges, differential pressure level gauges, float-type level gauges, electromagnetic level gauges

Based on their working principle, the main types of level measurement instruments are as follows: 1. Direct-reading level instruments: These include glass tube level gauges, glass plate level gauges, etc. 2. Differential pressure level gauges: These can be further divided into pressure-type level gauges and differential pressure type level gauges; they operate on the principle that a liquid column or a pile of material creates pressure at a certain point. 3. Buoyant level gauges: They operate on the principle that the height of a float changes as the liquid level changes, or that the buoyancy exerted by the liquid on a float (or sinker) submerged in the liquid changes with the liquid level. It can be further divided into types with a float equipped with a steel wire rope or steel strip, types with a float and a lever, and barrel-type types. 4. Electromagnetic level gauges: They convert changes in liquid level into corresponding changes in electrical quantities, and the level is determined by measuring these electrical changes. It can be divided into resistive (i.e., electrode-type), capacitive, and inductive level gauges, etc. There are also level gauges that operate using the magnetostrictive effect. 5. Nuclear radiation level gauge: It operates on the principle that the intensity of nuclear radiation decreases as it passes through a material layer, with this intensity varying depending on the thickness of that layer. Gamma rays are currently the most widely used. 6. Acoustic-type property meters: As changes in liquid level cause variations in acoustic impedance, as well as differences in the interruption of sound waves and their reflection distances, by detecting these changes it is possible to determine the liquid level. Therefore, acoustic level gauges can be classified into acoustic interruption type, reflection type, and damping type based on their working principles. 7. Optical level gauges: These work on the principle of light waves being blocked or reflected by the level of the substance present; the light source used can be an ordinary incandescent lamp or a laser, among others.

Float, radar, ultrasonic, pressure difference, capacitance

1. Direct-reading level gauges: These include instruments such as glass tube level gauges and glass plate level gauges. 　　2. Differential pressure level gauges: These can be further divided into pressure-type level gauges and differential pressure type level gauges; they operate on the principle that a liquid column or a pile of material creates pressure at a certain point. 　　3. Buoyant level gauges: They operate on the principle that the height of a float changes as the liquid level changes, or that the buoyancy exerted by the liquid on a float (or sinker) submerged in the liquid changes with the liquid level. It can be further divided into types with a float equipped with a steel wire rope or steel strip, types with a float and a lever, and barrel-type types. 　　4. Electromagnetic level gauges: They convert changes in liquid level into corresponding changes in electrical quantities, and the level is determined by measuring these electrical changes. It can be divided into resistive (i.e., electrode-type), capacitive, and inductive level gauges, etc. There are also level gauges that operate using the magnetostrictive effect. 　　5. Nuclear radiation level gauge: It operates on the principle that the intensity of nuclear radiation decreases as it passes through a material layer, with this intensity varying depending on the thickness of that layer. Gamma rays are currently the most widely used. 　　6. Acoustic-type property meters: As changes in liquid level cause variations in acoustic impedance, as well as differences in the interruption of sound waves and their reflection distances, by detecting these changes it is possible to determine the liquid level. Therefore, acoustic level gauges can be classified into acoustic interruption type, reflection type, and damping type based on their working principles. 　　7. Optical level gauges: These work on the principle of light waves being blocked or reflected by the level of the substance present; the light source used can be an ordinary incandescent lamp or a laser, among others.

The classification of electrical measuring instruments can be divided as follows: (1) By phase type: single-phase, three-phase three-wire, three-phase four-wire, etc. (2) Classified by function and purpose: active energy meters, reactive energy meters, maximum demand meters, multi-rate meters, multi-functional meters, copper loss meters, iron loss meters, etc. (3) Classified by working principle: inductive, electronic, electromechanical, etc. Technical requirements for various types of meters in power systems: (1) Power measurement devices connected to medium-voltage insulated systems should use three-phase three-wire active and reactive power meters. Electric energy metering devices connected to non-neutral-point insulated systems shall use three-phase four-wire active and reactive power meters, or three induction-type non-reverse single-phase meters. (2) For the 3 voltage transformers connected to a neutral-point-insulated system, a Y/y wiring configuration is recommended for those at 35 kV and above ； For voltages below 35 kV, a V/V wiring configuration is recommended. Three voltage transformers connected to a non-neutral-point insulated system should preferably be wired in a Y0/y0 configuration. Its primary side grounding method is consistent with the system grounding method. (3) For low-voltage power supply with a load current of 50A or less, a directly-connected meter is recommended ； When the load current is 50A or higher, it is advisable to use a wiring method with connection through a current transformer. (4) For electric energy metering devices with a three-phase three-wire connection, a four-wire connection should be used between the secondary windings of the two current transformers and the meter. For three-phase four-wire connected power metering devices, a six-wire connection should be used between the secondary windings of the three current transformers and the meter

Direct-reading, buoyancy, capacitive, static pressure, laser, echo reflection

1) Direct-reading level gauge; 2) Differential pressure level gauge; 3) Float type level gauge; 4) Electromagnetic level gauge; 5) Radar level gauge; 6) Acoustic wave level gauge; 7) Optical level gauge.

1. Direct-reading level gauge； 2. Differential pressure level gauge ； 3. Buoyant level gauge ； 4. Electromagnetic level gauges ； 5. Nuclear radiation type level gauge ； 6. Acoustic wave-type property meters ； 7. Optical object simulation instrument