If you’re working with X-ray inspection, you’ve probably come across two high-speed imaging technologies: Line Scan Detectors and TDI (Time Delay Integration) detectors.
So what’s the difference—and when should you use one over the other?
Let’s break it down with a visual explanation, technical insights, and a simple analogy.
1. Line Scan Basics: How It Works
A line scan detector is a type of X-ray sensor made up of one long column with multiple rows of pixels. Some may include a few adjacent columns, but the sensor is fundamentally very narrow—like a strip.
How are images formed?
As a sample moves across the detector, the sensor rapidly captures slices of the object—line by line—and assembles them into a complete image.
Frame rates can reach 12,000 to 24,000 lines per second, making this ideal for fast-moving objects on conveyor belts or long PCBs.
2. Enter TDI: Time Delay Integration
Time delay integration (TDI) is an advanced type of line scan sensor, specifically engineered for low-light or low-signal X-ray imaging environments.
Instead of capturing an image in a single column, TDI uses up to 150 columns. Here’s the magic: the signal from each row is passed down to the next column, in sync with the movement of the object, adding and amplifying the image as it moves through the detector.
This time delay integration technique offers several advantages:
Superior imaging of dense or low-contrast materials
Enhanced signal-to-noise ratio
Increased sensitivity to low X-ray signals
3. Visual Analogy: The Pixel Relay
Imagine a relay race where each runner passes the baton to the next.
- Line Scan: One runner runs the whole track, handing over slices of the image to memory.
- TDI: Each runner takes the baton and adds energy to it, handing off to the next until it crosses the finish line with full strength—producing a sharper, cleaner image.
4. When to Use Each Technology
Use Line Scan Detectors When:
- The object is well-lit with strong X-ray exposure
- Speed and throughput are priorities
- You’re scanning standard materials (e.g. electronics, food inspection)
Use TDI Detectors When:
- Imaging dense materials or low-luminosity samples
- High image clarity and minimal noise are critical
- Operating in environments with weak X-ray signals
🔍 Tip: Synchronization is key in TDI systems. The sample’s motion must match the rate of signal transfer across columns—or the image will turn out blurry.
5. Cost Consideration
TDI detectors are significantly more expensive than standard line scan systems. So while TDI offers better performance in specific conditions, a standard line scan is sufficient for most industrial applications, including:
- Airport security
- Food safety inspection
- Electronics manufacturing
Conclusion: When to Use Line Scan vs. TDI
While both TDI and standard line scan detectors offer high-speed, high-resolution imaging, they shine in different situations.
Use a line scan detector when speed, simplicity, and cost-efficiency are key—and your sample has good X-ray exposure.
Go with TDI when you’re dealing with low-light conditions, dense materials, or need enhanced image clarity and sensitivity.
Have questions about choosing the right X-ray system? Contact us at Creative Electron
