External clamp type ultrasonic flowmeterIt is a non-contact flow measurement instrument based on ultrasonic detection technology, which achieves accurate measurement of fluid velocity and flow rate by clamping it outside the pipeline. The core principle is the ultrasonic propagation time difference method or Doppler effect: when the ultrasonic pulse penetrates the pipe wall and fluid, there is a difference in the propagation speed in the forward and backward directions. By measuring the time difference, the fluid velocity can be calculated, and the volumetric flow rate can be calculated based on the known pipe diameter. Some models also integrate Doppler shift technology, which is suitable for measuring fluids containing particles or bubbles.
This device has significant technological advantages. Non contact design avoids medium pollution and pipeline modification, and can be directly installed in operating pipeline systems, especially suitable for corrosive liquids or high-pressure environments. Its measurement range covers pipe diameters from DN15 to DN6000, with a flow rate range of ± 32m/s. It supports uniform media such as water, oil, and chemical liquids, and is suitable for pipelines made of metal, plastic, cement, and other materials. The high-precision time to digital conversion chip and real-time temperature compensation technology enable measurement accuracy to be better than ± 1%, effectively overcoming small flow errors and zero drift problems.
External clamp type ultrasonic flowmeterStandard operating procedures:
1、 Preparation before measurement
Check equipment:
Confirm that the host, sensors (usually A/B or transmitter/receiver), signal cables, coupling agents, tool kits, and other accessories are complete.
Check if the battery is fully charged or connect to an external power source.
Understand the operating parameters:
Pipeline material: such as carbon steel, stainless steel PVC、 Cast iron, etc.
Outer diameter and wall thickness of the pipeline: measured accurately using a caliper.
Fluid types: such as clean water, sewage, seawater, oil, etc.
Lining and scaling situation: If there is lining or severe scaling, the thickness needs to be recorded.
Flow direction: Confirm the flow direction of the fluid inside the pipeline.
Choose the appropriate installation method:
Z-method (radial type): suitable for small pipe diameters (usually DN15-DN300), with probes installed in relative positions on both sides of the pipeline.
V method (reflective): Z is commonly used and suitable for medium pipe diameters (DN15-DN400). The probe is installed on the same side, and the sound wave is reflected once through the pipe wall.
W method (multi reflection): used for small diameter or low turbidity liquids, where sound waves are reflected multiple times inside the tube to increase signal intensity.
2、 Install sensors
Determine installation location:
Choose a location with a longer straight pipe section, generally requiring an upstream straight pipe section of ≥ 10D and a downstream straight pipe section of ≥ 5D (D is the diameter of the pipeline), to avoid interference sources such as elbows, valves, and diameter changes.
The surface of the pipeline should be flat, rust free, and without insulation layer (if any, it needs to be removed and ensure good coupling).
Avoid installing vertically upwards to prevent gas accumulation from affecting the signal.
Clean the surface of the pipeline:
Use sandpaper or polishing tools to remove paint, rust, and dirt from installation points, revealing a metallic luster.
Wipe clean with alcohol or a cleaning cloth to ensure a smooth surface.
Apply coupling agent:
Apply specialized ultrasonic coupling agent (such as silicone grease) evenly at the bottom of the sensor to prevent air from entering and affecting sound wave transmission.
The dosage of coupling agent is moderate to avoid excessive overflow.
Installing sensors:
According to the selected installation method (Z/V/W method), use a tape measure and installation fixture (or the distance calculated by a calculator) to determine the distance between the two sensors.
Place the sensor correctly in the direction of flow (usually indicated by arrows), secure it firmly with stainless steel tape or magnetic base, and ensure a tight fit with the pipeline.
Connect the sensor cable to the corresponding interface (Channel A/B) of the host.
3、 Parameter Setting and Measurement
Power on and enter parameters:
Turn on the power of the host.
Enter the following key parameters in sequence in the menu:
Pipe material
管道外径、壁厚
Lining thickness (if any)
Fluid type (or select 'water')
Installation method (Z/V/W method)
Sensor Model
flow direction
Signal debugging and optimization:
The host will automatically search for signals. Observe the signal strength (Signal Quality) and signal quality (Q value).
Ideal state: Signal strength>60%, Q value>6.0 (slightly different brand standards).
If the signal is weak, you can fine tune the sensor position, reapply coupling agent, and adjust the tightness of the fastening band until the signal stabilizes.
Start measuring:
After confirming that all parameters are correct and the signal is good, the instrument will automatically calculate and display:
Instantaneous flow rate (m ³/h, L/min, etc.)
Flow velocity (m/s)
Positive/negative cumulative flow
Data recording intervals can be set for long-term monitoring.
4、 Measurement post-processing
Read and record data:
Record measurement results, time, location, environmental temperature, and other information.
Supports USB drive export, Bluetooth transmission, or 4-20mA analog output (depending on the model).
Dismantling and Cleaning:
After the measurement is completed, turn off the power.
Remove the sensor, wipe off the coupling agent with a soft cloth, and clean the surface of the sensor.
Clean the pipeline installation point and restore the insulation layer if necessary.
Storage equipment:
Put sensors, cables, hosts, etc. into a portable case and store them in a dry, cool place.
The coupling agent is sealed and stored to prevent drying up.
5、 Precautions
Coupling agent is crucial: specialized coupling agents must be used, as ordinary oils or water cannot effectively transmit ultrasonic waves.
Avoid bubbles and particles: The presence of a large number of bubbles or suspended solids in the fluid can attenuate the signal and affect accuracy.
Regular inspection: During long-term online use, regularly check the fixing and coupling status of the sensor.
Calibration suggestion: Although external clamp flow meters generally do not require regular calibration, it is recommended to compare them with standard meters once a year to ensure accuracy.
Understanding limitations: Measurement accuracy is greatly affected by installation quality, pipeline conditions, and fluid characteristics, typically ranging from ± 1% to ± 5%.