Basic knowledge and comparison of several common f

2022-05-17
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Basic knowledge and comparison of several common flowmeters

basic knowledge and comparison of several common flowmeters

flow measurement is one of the four important process parameters (the other is temperature, pressure and material level). The closed pipe flowmeter is classified according to the technology adopted as follows:

differential pressure flowmeter (DP)

this is the most common flow technology, including orifice, venturi and sonic nozzle. DP flowmeter can be used to measure the flow rate of most liquids, gases and steam. DP flowmeter has no moving part, so it is widely used and easy to use. However, after plugging, it will produce pressure loss and affect the accuracy. The accuracy of flow measurement depends on the accuracy of the pressure gauge

volume flowmeter (PD)

PD flowmeter is used to measure the volume flow rate of liquid or gas. It introduces the fluid into the metering space and calculates the number of revolutions. Impeller, gear, piston or orifice plate are used to divert fluid. PD flowmeter has high accuracy and is one of several methods to measure viscous liquid. However, it will also produce unrecoverable pressure error and need to be equipped with moving parts

turbine flowmeter

when the fluid flows through the turbine flow meter, the fluid rotates the rotor. The rotational speed of the rotor is related to the speed of the fluid. The flow or total amount is derived from the average flow rate of the fluid felt by the rotor. Turbine flowmeter can accurately measure clean liquids and gases. Like PD flowmeter, turbine flowmeter will also produce unrecoverable pressure error and need to move parts

electromagnetic flowmeter

when the conductive fluid flows through the electromagnetic field, the velocity of the fluid can be obtained by measuring the voltage. The electromagnetic flowmeter has no moving parts and is not affected by the fluid. The accuracy of measuring conductive liquid when the tube is full is very high. Electromagnetic flowmeter can be used to measure the flow rate of slurry fluid

ultrasonic flowmeter

propagation time method and Doppler effect method are commonly used in ultrasonic flowmeter to measure the average velocity of fluid. Like other speed meters, it is an instrument for measuring volume flow. It is an unimpeded flowmeter. If the ultrasonic transmitter is installed outside the pipeline, it does not need to be inserted. It is applicable to almost all liquids, including slurry, with high accuracy. However, the dirt of the pipeline will affect the accuracy

vortex flowmeter

vortex flowmeter is to place a non streamlined vortex generator in the fluid, and the speed of the vortex is proportional to the speed of the fluid, so as to calculate the volume flow. Vortex flowmeter is suitable for measuring liquid, gas or steam. It has no moving parts and no dirt problems. Vortex flowmeter will produce noise, and the fluid is required to have a higher flow rate than its final target market and Meike 1 to generate vortex

thermal mass flowmeter

measures the fluid velocity by measuring the increase of the temperature of the fluid or the decrease of the thermal sensor. The thermal mass flowmeter has no moving parts or holes and can accurately measure the flow of gas. Thermal mass flowmeter is one of the few technologies that can measure mass flow, and it is also one of the few technologies used to measure large-diameter gas flow

Coriolis flowmeter

this flowmeter uses the deflection generated by the vibrating fluid pipe corresponding to the mass flow to measure. Coriolis flowmeter can be used to measure the mass flow of liquid, slurry, gas or steam. High accuracy. However, the pipe wall shall be maintained regularly to prevent corrosion

electromagnetic flowmeter

measurement principle: Faraday's law of electromagnetic induction proves that a conductor moving in a magnetic field will induce an electric potential. Using the principle of electromagnetic measurement, the fluid is the conductor in motion. The induced potential is proportional to the flow rate and detected by two measuring electrodes. Then the transmitter amplifies it and calculates the flow according to the cross-sectional area of the pipeline. A constant magnetic field is generated by switching DC current with alternating polarity. Master the high truth technology of the experimental machine

the measurement system consists of a transmitter and a sensor

it has two models: integrated type, in which the transmitter and sensor form an integral mechanical unit; Separate type, transmitter and sensor are installed separately

transmitter: promag50 (operated by button and displayed in two lines) sensor: promagw (DN25 2000)

technical parameters

measurement variable: flow rate

measurement range of input variable: typical v = 0. 110m/s with specified measurement accuracy

operable flow range: more than 1000:1

input signal status input (auxiliary input): u = 3 30VDC, RI = 5K, electrical isolation. Configurable: cumulative metering (s) reset, measured value suppression, error message reset. Current input (promag 53 only): active/passive optional, electrical isolation resolution: 2 A, active: 4... 20mA, RI 150, uout = 24V DC, anti current short circuit

passive: 0/4... 20mA,Ri 150 ,Umax=30V DC。

output variable

output signal current output: active/passive optional, electrical isolation, time constant optional (0.05... 100s), full scale value optional, temperature coefficient: typical 0.005% O.R./℃; Resolution: 0.5 A

active: 0 is equivalent to absorbing 1/4 of the excess capacity of crude steel/4 20mA, RL 700 (Hart: RL 250)

passive: 4 20mA, max.30vdc, RI 150

pulse/frequency output: passive, open collector, 30VDC, 250mA, electrical isolation

frequency output: full scale frequency 2 1000Hz (f max = 1250hz), opening/closing ratio 1:1

pulse width: max. 10s

pulse output: the pulse value and pulse polarity can be selected, the maximum pulse width can be set (0.05... 2S), the maximum pulse frequency can be selected from the transmitter shell, and the integrated shell: powder coated cast aluminum; Wall mounted housing: cast aluminum sensor housing, DN25 300: powder coated cast aluminum; DN350... 2000: coating steel

model specification: 50w9h-ud0a1ak2c4aw (dn900), 50W is 50 series; 9h means the diameter is 900mm (dn900); U indicates that the substrate material is polyurethane; D indicates that the process connection/material is PN 10 din250l, St flange (applicable to dn200-dn2000); 0 indicates that the electrode material (all electrodes) is 1.4435/316l stainless steel; A indicates that the calibration is 0.5%. 3-point calibration; 1. Indicate that special certification is not required; The second a indicates no riot control requirements; K indicates that the enclosure protection grade is IP68, separated and wall mounted; 2 refers to separate type with 10m cable

ambient conditions: ambient temperature - 20+ 60 ℃ (sensor, transmitter), installed in a dark place to avoid direct sunlight, especially in warm climate areas

reference conditions for measurement accuracy: comply with DIN 19200 and VDI/VDE 264l, medium temperature: + 28 ℃ K, ambient temperature: + 22 ℃ K, preheating time: 30 minutes,

during installation, it should be noted that accurate measurement can be obtained only when the pipe is full, and the following installation positions should be avoided: the highest point of the pipe (easy to collect bubbles) is directly installed in front of the open outlet of a downward pipeline

be careful not to install the flow pipe on the inlet side of the pump to avoid damage to the flow pipe lining caused by pumping pressure. When using reciprocating, diaphragm or plunger pump, it is necessary to install pulse throttle valve in the

when the length of the downward pipe exceeds 5m, install a siphon or a vent valve behind the sensor. To avoid possible damage to the measuring pipe lining caused by low pressure. Ensure full pipe and reduce gas content

installation orientation: the most suitable orientation can help avoid gas accumulation and residue accumulation in the measuring tube

vertical installation; This orientation is ideal for easy self emptying pipeline system, and empty pipe detection electrode can not be added

horizontal installation: the plane of the measuring electrode must be horizontal, so as to prevent short-term insulation of the electrode due to entrained bubbles. Note: the empty pipe detection function can work correctly only when the measuring device is installed horizontally and the transmitter shell is upward. If the vibration is very severe, install the sensor and transmitter separately

base, support: if the nominal diameter is DN 350, install the transmitter on a base that can withstand sufficient load. Note that the outer frame is not allowed to bear the weight of the sensor. This will deform the outer frame and destroy the internal excitation coil. If possible, it is best to avoid installing sensors, such as valves, tees, elbows and other components

ensure the following straight inlet and outlet pipe sections required to ensure measurement accuracy: inlet length 10 DN outlet length 5 DN sensor and transmitter grounding sensor are in the center of the pipe

grounding: the sensor and medium must have the same potential to ensure measurement accuracy and avoid electrode corrosion damage. The equipotential is guaranteed by installing a reference electrode in the sensor. If the medium flows in an unlined and grounded metal pipe, it can meet the grounding requirements by connecting to the transmitter housing. For separate grounding, the same as above

note: if it is not sure whether the medium is properly grounded, install the grounding ring

fault diagnosis:

electromagnetic flowmeter

if there is a fault after startup or during operation, the fault diagnosis is usually carried out according to the following checklist to directly find the cause of the problem and corresponding solutions

check display

no display and no output signal: 1. Check power terminals 1 and 2; 2. Check the fuse

no display but signal output: 1. Check whether the cable connection of the display module is correctly inserted into the amplification board; 2. The display module is damaged; 3. The measuring electrode is damaged

the display text is in foreign language: turn off the power supply, press and hold the +/- key and power on the measuring instrument. The display text will be in English (default) and at the maximum display contrast

the measured value is displayed, but there is no current or pulse output signal: the measuring electrode is damaged

display fault: the fault during debugging or measurement will be displayed immediately. The fault information will contain some symbols, which mean as follows: S = fault information, P = process fault

= fault information= Warning message empty pipe = fault type, i.e. measuring pipe is partially full or completely empty 03:00:05 = fault occurrence time, hour/minute/second #401 = fault code

current output: minimum current, 4-20mA (25mA) 2mA, and the output signal corresponds to zero flow

maximum current, 4-20mA (25mA)

note: system or process faults defined as warning messages have no impact on input/output

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