Q: <strong>Gas Turbine Flow Meter Working Principle</strong>

The gas turbine flowmeter uses a turbine for measurement . It first converts the flow rate into the rotational speed of the turbine, and then converts the rotational speed into an electrical signal proportional to the flow rate. Gas turbine flowmeter is used to detect instantaneous flow and total integrated flow. Its output signal is frequency, which is easy to digitize. The induction coil and the permanent magnet are fixed on the housing together. When the ferromagnetic turbine blade passes the magnet, the reluctance of the magnetic circuit changes, thereby generating an induction signal. The signal is amplified and reshaped by the amplifier and sent to the counter or frequency meter. The total accumulated flow is displayed. At the same time, the pulse frequency undergoes frequency-voltage conversion to indicate instantaneous flow. The speed of the impeller is proportional to the flow, and the number of revolutions of the impeller is proportional to the total amount of flow. The output of the turbine flowmeter is a frequency modulated signal. It not only improves the anti-interference of the detection circuit, but also simplifies the flow detection system. The gas turbine flowmeter has a turndown ratio of up to 10:1, and the accuracy is within ±0.2%. The time constant of the turbine flowmeter with small inertia and small size can reach 0.01 second.

Question 1

Gas Turbine Flow Meter Working Principle

Accepted Answer

The gas turbine flowmeter uses a turbine for measurement. It first converts the flow rate into the rotational speed of the turbine, and then converts the rotational speed into an electrical signal proportional to the flow rate.

Gas turbine flowmeter is used to detect instantaneous flow and total integrated flow. Its output signal is frequency, which is easy to digitize.

The induction coil and the permanent magnet are fixed on the housing together. When the ferromagnetic turbine blade passes the magnet, the reluctance of the magnetic circuit changes, thereby generating an induction signal.

The signal is amplified and reshaped by the amplifier and sent to the counter or frequency meter. The total accumulated flow is displayed. At the same time, the pulse frequency undergoes frequency-voltage conversion to indicate instantaneous flow.

The speed of the impeller is proportional to the flow, and the number of revolutions of the impeller is proportional to the total amount of flow. The output of the turbine flowmeter is a frequency modulated signal. It not only improves the anti-interference of the detection circuit, but also simplifies the flow detection system.

The gas turbine flowmeter has a turndown ratio of up to 10:1, and the accuracy is within ±0.2%. The time constant of the turbine flowmeter with small inertia and small size can reach 0.01 second.

Question 2

Liquid Turbine Flow Meter Working Principle

Accepted Answer

Liquid Turbine Flow Meter is a speed type flow meter based on the principle of torque balance.

The fluid flows through the sensor housing. Because the blades of the impeller have a certain angle with the flow direction. The impulse of the fluid makes the blades have a rotational torque. After the friction torque and fluid resistance are overcome, the blades rotate. The speed is stable after the torque is balanced.

Under certain conditions, the speed is proportional to the flow rate.

Due to the magnetic permeability of the blade, it is in the magnetic field of the signal detector (composed of permanent magnets and coils). The rotating blade cuts the magnetic lines of force. The magnetic flux of the coil is periodically changed. Electrical pulse signals are induced at both ends of the coil.

This signal is amplified and reshaped by an amplifier. A continuous rectangular pulse wave with a certain amplitude is formed. It can be transmitted to the display instrument remotely. The instantaneous flow or total amount of the fluid is displayed.

Within a certain flow range, the pulse frequency f is proportional to the instantaneous flow Q of the fluid flowing through the sensor. The flow equation is:

Where:
f——Pulse frequency [Hz]
k——The meter coefficient of the sensor [1/m3], which is given by the calibration sheet.
Q——The instantaneous flow of fluid (under working condition) [m3/h]
3600-conversion factor in seconds

The meter coefficient of each sensor is filled in the verification certificate by the manufacturer. The k value is set in the matching display instrument. The instantaneous flow and cumulative total can be displayed.

Extended reading: Turbine Insertion Flow Meter for Large Diameter Pipeline

Question 3

What is k factor in turbine flow meter?

Accepted Answer

What is k factor in turbine flow meter?

The physical meaning of the meter coefficient K value of a turbine flowmeter is the number of pulses generated by a unit volume of fluid flowing through the flowmeter. Using the international system of units, the unit of the meter coefficient is (1/m3).

Generally, the K factor will not change when the flow rate changes, but it should not exceed the upper limit of the flowmeter too much. The K factor is a constant based on a flow rate under certain process parameters.

Question 4

How to get k factor on turbine flow meter?

Accepted Answer

How to get k factor on turbine flow meter?

There are two kinds of different manufacturers k:
One is k=f/Q, that is, the number of vortices generated per unit flow;
The other k=Q/f, that is, the plate flow rate corresponding to each vortex.
The k value is calibrated with the right factory water. The sensor measures the vortex number of the instrument and compares it with the volume flow measured by the calibration device to obtain the k value.

The k value is actually related to the internal mechanical structure of the flow meter measuring tube.
Taking k=f/Q as an example, the formula is as follows:

Where

D-measuring tube diameter
St-Strouhal number, constant within a certain range of Reynolds number
d----The characteristic width of the vortex generator
m---The ratio of the arcuate area on both sides of the vortex generator to the cross-sectional area of the pipe

In fact, this formula has no practical meaning for you. The values of d and m are difficult to measure accurately. Therefore, it is difficult to obtain an accurate k value by calculation.

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