Basler L301kc Line Array Camera Technology and Troubleshooting

Basler L301kc Three Line Color Line Array Camera Technology and Application

In the field of high-speed industrial visual inspection, color line array cameras have become an ideal choice for applications such as print inspection, textile sorting, flat panel display quality inspection, and postal sorting due to their continuous scanning, high resolution, and excellent color reproduction capabilities. Basler L301kc, as a Camera Link interface linear array camera based on Kodak KLI-2113 three line CCD sensor, occupies an important position in early high-end detection systems with a 2098 pixel x 3 line array, 8kHz line frequency, and flexible spatial correction function. With the increasing demand for maintenance of discontinued models, on-site engineers often face challenges such as designing spatial calibration parameters, selecting output modes, configuring serial ports, and troubleshooting. This article is based on the complete user manual of L301kc, comprehensively analyzing its core technology, configuration methods, and on-site debugging points from the perspective of system integration, providing practical reference for engineers who maintain and replace the camera.

Product positioning and core specifications

Basler L301kc is a three line color line array camera equipped with Kodak KLI-2113 trilinear CCD image sensor, with 2098 effective pixels per line, pixel size of 14 μ m × 14 μ m, and RGB three line center spacing of 112 μ m. This camera is designed specifically for industrial environments and has the following outstanding features:

High sensitivity and high signal-to-noise ratio: 100% fill factor, typical light response non-uniformity<5%

Multiple output modes: Supports 20MHz 8-bit RGB mode, 60MHz single pixel/40MHz dual pixel 8/10 bit mode

Electronic exposure control: supports ExSync edge control, level control, programmable mode, and Free run internal triggering

Spatial Correction: Achieving precise color alignment through programmable delay compensation of RGB trilinear physical spacing

AOI (Area of Interest): The starting pixel and length can be specified to reduce data processing complexity

Digital Shift: signal multiplication achieved through bit operations (2X/4X/8X)

Programmable gain and bias: RGB three-way independent adjustment, supporting fine white balance adjustment

Key performance parameters:

Pixel clock: 20MHz (8-bit RGB), 40MHz (dual pixel mode), 60MHz (single pixel mode)

Maximum line frequency: 8.0kHz (spatial correction enabled)/9.20kHz (spatial correction disabled)

Minimum line frequency: 1kHz

Power consumption:<5.1W @ 12VDC

Working temperature: 0 ° C to+50 ° C (shell temperature)

Dimensions: 38.1mm × 62mm × 62mm (excluding F-port adapter)

Sensor architecture and signal chain

The sensor of L301kc consists of three independent pixel lines, covering red, green, and blue filters respectively. Each line contains 2098 photodiodes, which are transferred to their respective shift registers after charge accumulation. After variable gain control (VGC) amplification, they are digitized by a 10 bit ADC.

Due to the physical distance of 112 μ m between the three RGB lines (equivalent to 8 pixel intervals, 14 μ m/pixel), the same object point is captured by the three lines at different times in the scanning motion direction. If output is not processed directly, it will result in serious color misalignment ("rainbow effect"). L301kc uses internal FIFO memory to delay the first two channels of data, realigning RGB information before output - this is the core principle of the "spatial correction" function.

Space Correction: Principles and System Design

Space correction is the core technology that distinguishes L301kc from ordinary linear array cameras. Users need to configure two key parameters based on the actual system configuration:

3.1 Starting Line for Space Correction

Determine the 'crossing direction' of the image on the sensor:

If the direction of object motion causes the image to pass through the red line first (when using an objective lens), the starting line is set as the red line.

If it passes through the blue line first, it is set as the blue line.

3.2 Delay in Lines for Space Correction

Specify the time offset when combining RGB trilinear data. For example, if the delay is set to 8, the blue line data is combined with the green line data captured 8 rows ago and the red line data captured 16 rows ago to form a complete RGB pixel.

3.3 System design calculation formula

The manual provides precise optical mechanical matching formulas:

Magnification factor: β=112 μ mn × Δ y, where n is the number of encoder steps (1-16) required to move the image from one line to another, and Δ y is the distance of object movement corresponding to each step.

Field of view length: L=29.372mm × β 1 (effective sensor length=2098 pixels × 14 μ m)

Aspect ratio: directly determined by n, achieving a 1:1 ratio when n=8.

Engineering example: Assuming the encoder has a step size of 0.2mm and a target aspect ratio of 1:1, then n=8, the calculated magnification is 1:14.29, and the single line field of view is 419.6mm. If the sensor needs to cover a 350mm wide conveyor belt, the required n value can be calculated in reverse and the optical magnification can be adjusted.

Important constraint: Spatial correction is only available in 8-bit output mode and automatically disabled in 10 bit mode. Test image modes 1 and 2 will also force the delay to be set to 0 (disable spatial correction).

Output mode selection and data timing

L301kc provides five output modes to adapt to different frame acquisition card bandwidths and processing capabilities:

Mode Pixel Clock Data Bit Depth per Cycle Application Scenarios

20MHz 8-bit RGB 20MHz RGB three pixel simultaneous 8-bit standard color acquisition, good compatibility

60MHz single pixel 8-bit 60MHz single channel/cycle 8-bit high-speed transmission, requiring a high bandwidth acquisition card

60MHz single pixel 10 bit 60MHz single channel/cycle 10 bit high dynamic range, requires a 10 bit acquisition card

40MHz Dual Pixel 10 Bit 40MHz Dual Channel/Period 10 Bit 10 Bit Bandwidth Compromise Solution

High speed compromise solution for 40MHz dual pixel 8-bit 40MHz dual channel/cycle 8-bit 8-bit

The data output sequence is fixed as red → green → blue, and the Line Valid (LVAL) signal remains high during effective data transmission. The frame acquisition card needs to correctly parse the row data based on the LVAL signal.

Detailed explanation of exposure control mode

5.1 ExSync external synchronization mode

Triggered by external ExSync signal control line:

Edge control: The exposure time is equal to the ExSync cycle (rising edge to rising edge), and the charge accumulates throughout the entire cycle.

Level control: The exposure time is determined by the ExSync low-level time, and charges only accumulate during the low-level period.

Programmable control: The rising edge triggers the start of exposure and lasts for a preset time (Timer 1 setting), commonly used in scenes that require precise exposure time.

5.2 Free run mode

No external synchronization required, continuous trigger signals are generated by internal Timer 1 and Timer 2:

Edge control: The exposure time is equal to the internal period.

Programmable control: Timer 1 sets the low-level time (i.e. exposure time), Timer 2 sets the high-level time.

Key limitation: Maximum line frequency of 8.0kHz (space correction enabled) or 9.20kHz (disabled), exceeding the limit will trigger a "line frequency exceeding" error, and some lines will output all zero values.

Image quality tuning: gain, bias, and digital shift

6.1 Gain and bias settings

Gain: adjustable range of 96-1023 (decimal), corresponding to 0dB to 33.6dB. As the gain increases, both the signal and noise are amplified simultaneously, while the SNR remains basically unchanged. It is recommended to prioritize adjusting brightness through lighting and exposure time rather than relying on gain.

Offset: Adjustment range 0-255 (decimal). In 10 bit mode, every 4 units of bias increase the output by 1 DN value; Add 1 DN value for every 16 units in 8-bit mode.

White balance adjustment suggestion: First fix the gain of the channel with the strongest response, and then adjust the other two channels to make the RGB values of the white object equal.

6.2 Digital Shift

By changing the output bit mapping to achieve signal multiplication, it is suitable for improving brightness under low light conditions:

No displacement: Normal output ADC original 10 bits or high 8 bits

Displacement once (2X): Discard the most significant bit and output the second highest bit to LSB

Displacement twice (4X): Discard the higher two digits

Displacement three times (8X): Discard the high three digits

Pre use verification: In 8-bit mode, if the maximum pixel value exceeds 128, 2X displacement cannot be used; If it exceeds 64, 4X cannot be used; if it exceeds 32, 8X cannot be used, otherwise it will cause saturation limiting (high position 1 and low position 1).

Area of Interest (AOI) and Test Images

7.1 AOI Function

You can specify the starting pixel (1-2098) and length (1-2098), and only output pixel data within the specified range. Attention: AOI will not increase the maximum line frequency, but it can reduce the amount of data transmitted per line and lower the processing pressure on the acquisition card.

7.2 Test Images

Built in 6 types of test images:

Grayscale gradient (full channel)

Vertical movement grayscale gradient

Horizontal grayscale gradient (used to verify whether spatial correction is effective)

red gradient

green gradient

blue gradient

Test image 3 can be used for intuitive verification of spatial correction delay settings: when delay=0, the RGB values of the left and right halves of the image are equal; When the delay is 8, the RGB values of the same pixel in the right half differ by 8 DN.

Configuration method: CCT+tool and binary protocol

8.1 Camera Configuration Tool Plus（CCT+）

A graphical Windows tool that communicates with the camera via Camera Link serial port (RS-644). Parameter grouping management (output, exposure, gain/bias, AOI, etc.), with immediate effect upon modification. Support saving work configurations to one of 15 user configuration groups and setting a Startup Pointer to determine which configuration group to load when powered on.

8.2 Binary Command Protocol

Suitable for automation integration, sending frame format commands through Camera Link standard API (clser *. dll) or Basler CPA driver:

Frame structure: STX (0x02)+2-byte descriptor (command ID, read-write flag, data length)+data+BCC checksum+ETX (0x03)

Verification method: XOR checksum of descriptor and data byte

Response: ACK (0x06) or NAK (0x15); Read command returns data frame

Typical Command Example (Read Camera Status): 0x02, 0x43, 0x82, 0xC1, 0x03

Section 4.2 of the manual provides a detailed list of all configuration commands (output mode, exposure mode, Timer settings, gain/bias, etc.) AOI、 Command IDs and data formats for spatial correction, digital shift, test images, configuration set operations, etc.

Troubleshooting and LED status indication

The LED on the back of the camera provides quick diagnosis:

Meaning of LED status

Always bright orange and running normally

Flashing 3 times, ExSync signal remains unchanged for 5 seconds (normal if not wired)

Flashing 5 times, Work Set cannot be saved to User Set

Flashing 6 times, the User Set or Factory Set cannot be loaded into the Work Set

Flashing the command list 7 times is invalid

Flash FPGA configuration failed 8 times

Common problem handling process:

No image: Check the power supply (12V ± 10%,>10.8V), Camera Link cable, ExSync signal (if used), and acquisition card configuration.

Poor image quality (color cast/ghosting): Check spatial correction parameters (number of delay lines/starting line), IR filter (filtering out>700nm infrared), mechanical installation (parallelism and perpendicularity between sensor and conveyor belt), and encoder signal stability.

Serial communication failure: Check if the baud rate (default 9600), frame format (8N1), and frame acquisition card DLL exist.

Mechanical installation and precautions

Installation dimensions: 62mm × 62mm × 38.1mm (excluding adapter), with 4 M4 mounting holes on the front end and 2 M4 holes on each side.

Sensor positioning accuracy: horizontal/vertical deviation ± 0.1mm, rotation deviation ± 0.2 °.

F-port adapter: Extend the total length to 69.6mm.

Important Warning:

Immediately install the lens after powering on to prevent dust from contaminating the sensor.

The polarity of the power supply cannot be reversed (PIN1/2 is+12V, PIN5/6 is GND), and there is no overvoltage protection (>14V damage).

The casing is not grounded, and the circuit board is isolated from the casing.

It is recommended to use an IR cut-off filter (such as B+W486) to maintain spectral balance.

Suggestions for replacement and upgrade

Considering that L301kc has been discontinued, if replacement or upgrade is required, the following path can be considered:

Basler racer series (such as raL2048-48gm): GigE interface, 2048 pixels, supports spatial correction, but interface and software compatibility need to be re evaluated.

Basler runner series (such as runner RL2048-48gm): also supports three line color, GigE Vision standard, and Pylon SDK support.

Third party compatible camera: It is necessary to confirm that the sensor spacing, pixel size, line frequency, and triggering method match the original system.

When replacing, special attention should be paid to:

Is the spatial correction delay algorithm compatible (the original system relies on FIFO delay in 8-bit mode)

Output mode matches the interface of the acquisition card (Camera Link or GigE)

Mechanical installation dimensions and lens interface (F or C port)