Vortex Flowmeter Fault Analysis and Treatment Measures

First, vortex flowmeter measurement principle

The basic principle of the vortex flowmeter is the phenomenon of Karman vortex street. The vortex street is generated alternately on both sides of the vortex generating body and forms a vortex street downstream of the main body (as shown in the figure). The frequency of the vortex separation is proportional to the flow velocity and inversely proportional to the width of the vortex generator. It can be expressed by the following formula: F=St·V/d ············

Where: F - vortex separation frequency

St - dimensionless constant (Stauhal)

V - Velocity of the vortex generator

D—the width of the inflow surface of the vortex generator

By measuring the separation frequency of the vortex, the fluid flow rate and instantaneous flow rate can be measured. The Strouhal number St is a dimensionless constant that can be experimentally determined. The linear part of the relation between the dimensionless constant St and the analogous No function is the linear measurement range of the vortex flowmeter. When the frequency F is detected, the velocity of the fluid in the tube can be obtained, and then the volumetric flow rate can be obtained from the flow velocity. The ratio of the number of pulses output over a period of time to the volume of the fluid (the number of pulses flowing through a unit volume of fluid) is called the meter coefficient (K-factor).

K=N/Q ·········· Formula (2)

Where: K—meter factor (pulse/M3)

N-pulse number

Q—fluid volume (M3)

The vortex separation frequency used to measure the flow rate varies with the flow rate and is not affected by the fluid density and viscosity. The pressure pulsation generated by the vortex separation is detected by the pressure sensitive sensor and converted into a pulse signal corresponding to the vortex frequency in the detection circuit. The signal converter converts this pulse signal into a 4-20 mA standard current signal output.

Second, install

2.1 Installation Instructions

The vortex flowmeter can be installed outdoors or outdoors. The flowmeter is best installed in a place where the vibration is small to prevent the vibration from affecting the accuracy of the measurement. When the pipeline vibration is large, the pipe should be installed and supported; if the pipe is always full of the measured medium. Liquids, then the pipe can be installed vertically or at any angle; the inner diameter of the flowmeter's connecting pipe must be slightly larger than the inner diameter of the vortex meter, within the range of (1-10mm). Ideally, an energy storage device can be installed upstream of the flow meter, which can reduce the vibration of the liquid and improve the measurement accuracy.

2.2 Reducing tube, expanding tube, bending tube

Corresponding to the shrink tube, it is necessary to ensure that the length of the straight pipe section measured upstream should be at least 25D, and the length of the straight pipe section measured downstream should be at least 5D; corresponding to the pipe expansion, the length of the straight pipe section measured upstream should be at least 25D. The length of the straight pipe section measured downstream shall be at least 5D. Corresponding to each section of the elbow, it must be ensured that the length of the straight section measured upstream of it should be at least 25D, and the length of the straight section measured downstream should be at least 5D. (D: nominal internal diameter of vortex flowmeter)

2.3 valve positioning and pipe length and temperature measurement pressure point selection

(1) The valve should be installed downstream of the flowmeter. The length of the upstream straight pipe segment depends on the upstream pipe condition (such as shrinkage pipe, pipe expansion, elbow pipe, etc. The length of the downstream straight pipe segment should be at least 5D. (2) If the valve Must be installed upstream of the flowmeter, then ensure that the length of the straight section upstream is at least 50D, and the length of the straight section downstream should be at least 5D. When pressure measurement is required, set the pressure measurement point upstream of the flowmeter 1D-3D Between the place; temperature measurement, the temperature measurement hole set in the downstream 3D-5D of the flowmeter.

2.4 Effect of Pulsating Flow on Flow Measurement

Fluids may vibrate strongly on high pressure liquid lines using piston or roots blowers or air compressors or high-pressure liquid lines using piston or column pumps. Usually, the valve should be installed upstream of the flowmeter. If you have to install the flowmeter upstream of the valve, you can install a pulsating flow attenuator upstream of the flowmeter, such as a throttle plate or expansion fracture, in the use of T-type In pipelines, the valve is installed in front of the flowmeter to avoid pulsation pressure fluctuations, leading to zero fluctuations of the instrument.

Third, failure analysis and treatment measures

3.1 Pipe Flow Meter No Output

phenomenon

the reason

Testing methods

Treatment measures

Pipe flow meter without output

Instrument no display no output

1, power failure

Detect the power supply voltage with a multimeter

Re-power or replace the power

2, the power supply is not connected

Detect the power supply voltage with a multimeter

Power on

3, the connection cable is broken or the wrong line

Check if the line is unblocked

Reconnect and check the cable

Instrument shows no output

1, the flow rate is too low, did not enter the measurement range

Increase the flow to see the display

Increase flow or reselect flow meter

2, a certain level of the amplifier board is faulty

Check with other type of flowmeter board replacement at the site

Replace the motherboard

3, the probe body has damage

First, increase the flow rate, replace the vortex motherboard with the same type of vortex street, if you exclude the motherboard failure, check the probe signal

Replace the probe

4, the pipeline is blocked or the sensor is stuck

If all of the above reasons, please check the installation of pipelines and meters

Reinstall the instrument

3.2 No flow after power on but output

phenomenon

the reason

Testing methods

Treatment measures

No flow after power on but output

The output signal is stable

1, the output frequency of 50 Hz power frequency interference

Use a multimeter to check the frequency

Use shielded cable to reconnect according to regulations

2, the output frequency is any constant frequency or constant output current value (damage of the amplifier board, resulting in self-excitation)

Check whether the output current of the main board is a constant value or the pulse is a constant value

Replace the amplifier

Output signal changes

1. Strong flow devices or high-frequency interference near the flowmeter

Check if there is such equipment around

Reselect installation location

2, the pipeline has a strong shock

Feel the concussion of the pipe by hand

Reinforces the piping of the flowmeter installation section

3, amplification board amplification or trigger sensitivity is too high

Commission GB and SB check output signal

Counterclockwise Decrease Magnification (GB) or Sensitivity (SB)

4, the pipeline valve is not completely closed, there is leakage flow

Check pressure and valve closure

Check valve

3.3 Unstable flow output

phenomenon

the reason

Testing methods

Treatment measures

Unstable flow output

Selection installation is extremely piping reason

1, there is a strong electrical interference signal, the instrument is not grounded, flow and interference signal superposition

Check ground

Reconnect

2. Insufficient straight pipe section or inner diameter of the pipe is inconsistent with the inner diameter of the meter

Check the inner diameter of the pipe and the inner diameter

Replace the installation position again

3, the impact of pipeline vibration

Feel the concussion of the pipe by hand

Reinforce pipes to reduce vibration

4, flow meter installation of different hearts

Remove the instrument to check the position of the flange and pipe

Reinstall the instrument

5, the fluid is full

Check fluid flow conditions extremely instrument installation position

Reinstall the instrument

6, the flow rate is lower than the limit or exceed the upper limit

Check fluid flow and gauge range

Increase the decrease flow or adjust the amplification board filter parameter K1 K2 K3

7. There is cavitation in the fluid

Check fluid condition

Install downstream valve on the instrument to increase back pressure

Instrument reason

1, the instrument menu settings are wrong

Check the instrument menu settings

Re-set the menu as required

2, the motherboard is damaged

Replace the motherboard to check if the flow shows no change

Replace the motherboard

3.4 Meter Display Flow and Process Flow Do Not Match

phenomenon

the reason

Testing methods

Treatment measures

The meter display flow does not match the process flow

Instrument reason

1, the flow meter failed to work

Check meter settings

Re-installation requirements set and refer to the three treatment methods

2,4-20mA full-scale setting error

Check the full scale setting

According to the actual amount according to the instructions to reset the full range

Selection design reason

1. The measurement gas or steam is not compensated in real time or fixed temperature pressure is set to compensate

Check the temperature compensation element and its settings

Add a warm pressure compensation element or set a fixed value compensation

2. Measuring gas or steam temperature measuring pressure element installation method or installation position is incorrect

Check the temperature compensation element and its settings

Reinstall the temperature and pressure compensation components as required

3. The user accounts for the flow of the meter with the rated output of the equipment

Check the rated output of the device

Recalculate process flow

4, saturated steam is not saturated

Check steam process

Changing process conditions


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