Essential Guide to Selecting Laser Sensors

In industrial environments, the most common laser device is the laser sensor (also called a laser distance sensor). It performs non-contact measurements of displacement and other quantities, and is widely used to measure displacement, thickness, vibration, distance, diameter and related geometric parameters.

A laser sensor uses laser emission, optical components, and photodetectors to convert a measured physical quantity (such as length, distance, vibration, flow, or speed) into an optical signal. A photodetector converts the light signal to an electrical signal that is filtered, amplified, and processed to produce a measurement output.

Compared with ultrasonic, infrared, and millimeter-wave sensors, laser sensors offer superior measurement accuracy, resolution, anti-interference performance, stability and response speed. Therefore, when precision requirements reach 0.1 mm or 0.01 mm, laser sensors are usually the engineers' first choice.

How do we choose among many available products?

First, fully understand the application scenario.

Below are four key points for scenario-based selection and explanations of common parameters found on datasheets.

1. Full scale (measuring range)

· The sensor's rated effective measurement range.

· The target's step height or movement must fall within the specified full scale when selecting a product.

2. Repeatability

When measuring with a laser sensor, readings will show small fluctuations even when the target is stationary. Repeatability is the range of variation in repeated measurements at the same position under fixed conditions — essentially the maximum fluctuation of the measured value.

※ Reference values assume an average sampling count (e.g. n = 4096). Always indicate measurement conditions: average sampling count = n.

3. Sampling frequency

Sampling frequency (Hz) denotes measurements per second. A higher sampling frequency shortens the time per measurement and suits high-speed targets. Note that faster sampling reduces received light per sample; take care when measuring low-reflectivity objects (e.g., black rubber).

⭐ Our laser sensors control received light by limiting exposure time, avoiding saturation even when emission duration is long.

Sampling frequency (Hz) = 1 / sampling period (ms/us)

4. Resolution

Resolution is the smallest increment the sensor can detect. For example, resolution = 1 mm means the sensor differentiates 1 mm steps.

5. Received light waveform

The received waveform shows the detector's received light position and intensity; the waveform peak indicates the measured value. A stable peak enables stable measurement.

※ Laser sensors often include automatic received-light feedback, so waveform monitoring is usually unnecessary. However, check the waveform in these cases and adjust mounting if needed to improve the waveform.

⭐ Measuring transparent materials

When measuring transparent targets, tilt the sensor so the receiver captures specular reflections. Allow a tilt margin (typically 2–5° depending on model) and verify the received waveform. For thickness measurement, the receiver can capture both front and rear surface reflections.

⭐ Measuring low-reflectivity (dark) targets

Short sampling periods reduce received light; when measuring dark materials or high-speed targets, confirm the received waveform to ensure sufficient signal.

⭐ Measuring highly reflective metals

High-reflectivity metals can easily saturate the receiver. If the waveform indicates saturation, reduce laser intensity or adjust mounting to lower received light.

6. Average sampling count

Even with a stationary target, repeated measurements fluctuate. Averaging n samples stabilizes the output. Increasing average sample count reduces fluctuation but may affect transient or edge detection.

Example: average sampling count = 4

Processing chart for average sampling count:

7. Linearity

Linearity is the error between measured and actual displacement. The horizontal axis is actual distance and the vertical axis is the sensor reading; the dashed line indicates maximum deviation from the ideal line.

If measurements were perfect, the actual distance and sensor reading would coincide as the ideal line. In practice, deviations from the ideal are linearity errors.

Linearity is typically expressed as a percentage of full scale. Longer full scale makes it harder to guarantee precision, so representing linearity as a percentage of full scale gives a clearer performance indication.