Laser Doppler Velocimeter (LDV)

Industrial Applications

• Metallurgical Industry:

MKK-LDV-08 series: This series is suitable for manufacturing various metal products such as wire, plate, strip, hot-rolled, cold-rolled, and pipes. It provides real-time online accurate measurement of speed and length, and can measure steel billets at temperatures above 1000℃.

MKK-LDV-08: Dedicated for continuous casting production lines, it can measure steel billets at temperatures above 1000℃, adapts to lower speed measurements, and employs automatic gain control for iron oxide scale surfaces. Measurement accuracy can reach ±0.1% (this accuracy for continuous casting production lines is 3 times higher than foreign brands).

• Bar Rolling Production Line Measurement: On continuous rolling bar rolling lines, finished bars move at high speed in the groove and vibrate up and down. Conventional Doppler velocimeters lose signals due to bar vibration, making accurate length measurement impossible.

The MKK-LDV-08 series features an anti-vibration design, allowing a vibration range of ≤10mm. It can accurately measure the speed and length of bars moving at high speed and vibrating up and down simultaneously, effectively solving the length measurement problem on bar rolling production lines.

• Paper Packaging Industry Fixed-Length Cutting:

1. Non-contact measurement with cardboard, avoiding cardboard indentation problems.
2. Cross-cutting length can reach ±0.5mm.
3. No cumulative error; high-precision cutting can be achieved regardless of size.
4. Avoids the cost of mechanical equipment wear and tear.
5. Avoids labor costs associated with returns and handling issues related to measuring wheels (indentation, gap adjustment, wear, etc.).

• Length measurement of various materials such as textiles, paper, and wood.

• Surface inspection: The MicroCenti laser Doppler velocimeter measures the speed and length of objects online. The editable pulses emitted by the velocimeter trigger the camera to acquire images. Regardless of speed changes, it ensures the acquisition of a clear, proportionally scaled image of the measured object’s surface, thus achieving defect identification.

• Provides speed and position information for laser marking machines, etc.: The MicroCenti laser Doppler velocimeter accurately provides precise speed and position information. The editable pulses drive laser marking machines to produce high-precision text, logos, QR codes, etc., with uniform processing results.

• Instantaneous speed measurement: Ultra-fast sampling frequency, 50,000 times/second. The MS-S-InstantS velocimeter is suitable for instantaneous speed measurement. With a sampling frequency of 50,000 times per second and a sampling time of up to 0.01ms, it can measure instantaneous speeds up to 300m/s. It can output multiple pulses, allowing for the measurement of the instantaneous speed of high-speed moving objects only a few centimeters long in an extremely short time.

Examples include: high-acceleration motion of cylinders and pistons, and instantaneous speed measurement of Hopkinson rods.

• Materials such as thin films and cables.

Applications in the rail transit field:

• Train speed measurement and positioning. The speed range measured by MicroCenti is directly proportional to the measurement distance, determined by the Doppler principle. An example using a measurement distance of 50cm is given below.

The MKK-LDV-08 can measure speeds in the range of 0-160km/h, with a minimum speed measurement of 0; suitable for speed measurement and positioning of medium- and low-speed rail trains such as subways and urban rail.

The MKK-LDV-08 can measure speeds in the range of 0-400km/h, with a minimum speed measurement of 0; suitable for high-speed speed measurement and positioning of high-speed trains.

The MKK-LDV-08 can measure speeds in the range of 0-1100km/h, with a minimum speed measurement of 0; suitable for speed measurement and positioning of ultra-high-speed maglev trains.

• Train Inspection and Condition Monitoring

The MicroCenti Doppler velocimeter, combined with machine vision technology, enables dynamic detection of trains without stopping operation.

Pulses emitted by the velocimeter trigger a high-speed linear array camera array to capture images of the detected area. The captured images exhibit excellent consistency, remaining undistorted even with significant speed changes.

The MicroCenti Doppler velocimeter is equipped with a powerful software analysis system, allowing for precise parameter settings and ensuring stable and accurate measurements.

Working Principle

The MicroCenti is a dual-beam laser Doppler velocimeter system that uses a phase modulator for frequency shifting and a Fast Fourier Transform (FFT) for frequency detection, thereby achieving speed measurement. It applies the differential laser Doppler principle. The light emitted from the DFB laser is split into two beams and then converges again on the surface of the object being measured. The detector receives the reflected light. When the lateral velocity of the object is zero, the reflected light and the detector light have the same frequency; when the lateral velocity is not zero, the reflected light undergoes a frequency shift relative to the detector light, fp = (2sinφ/λ)∙v. The speedometer calculates the frequency shift using a fast Fourier transform to determine the lateral velocity of the object being measured.

 Schematic diagram of the differential Doppler effect

Model Classification

The diagram below shows the output AB pulse: pulse output 5V, 24V selectable

Images of the cable industry

Metallurgical industry

• VelACS Speed Acquisition and Calculation System

Utilizing a multi-channel high-speed pulse synchronous acquisition system, this system ensures synchronized speed measurement from multiple MicroCenti tachometers. It accurately measures the speeds output by different tachometers at the same time and the speed differences between them, making user applications more precise and simpler.

The VelACS system can simultaneously connect to up to four MicroCenti tachometers via pulses.

It supports all PLCs and reads data via standard Modbus TCP protocol or Modbus RTU(485).

1. Elongation Measurement: Users can directly read the calculated speed difference data via the Modbus TCP protocol.

2. Redundant Speed Measurement with Multiple Speed Meters: The VelACS system can automatically identify and extract the optimal Doppler signal from multiple MicroCenti speed meters to calculate the most accurate speed and length data of the current object’s motion.

Suitable Scenarios: Bar Measurement, Rail Transit Speed Measurement

Dedicated Speed Meter for Bar Production Lines 

1. On continuous rolling bar production lines, finished bars move at high speed in the groove and vibrate up and down. Conventional Doppler speed meters lose signals due to bar vibration, making accurate length measurement impossible.

The MKK-LDV-08 series adopts a dual-optical-path technology solution and anti-vibration design, accurately measuring the speed and length of bars moving at high speed and vibrating up and down simultaneously, effectively solving the length measurement problem on bar production lines.

2. Bar length measurement scheme with redundant multiple tachometers and VelACS system: Two MKK-LDV-08 tachometers (or more) are installed on a bar production line and connected to the VelACS system simultaneously. One tachometer is the primary sensor and the other is the secondary sensor. When the primary sensor signal strength is insufficient but the secondary sensor signal is normal, the VelACS system automatically calculates the speed based on the secondary sensor. When the primary sensor Doppler signal is normal, the system automatically switches back to the primary sensor. This redundant speed measurement scheme makes the measurement on the bar production line more reliable and stable.