Frequently Asked Questions

What is a CIS sensor?

A CIS scanner is a compact line scan camera which is mounted directly above the object under inspection. It is the same type camera used in many fax or document scanners. The CIS consists of a row of silicon photodiodes, a graded index (GRIN) lens array and a light source.

What is the difference between a CIS and a conventional line scan camera?

The sensor of a conventional line scan camera is small (10 – 50 mm length) with small pixels (5 – 20 µm). The image is produced by reducing optics. The sensor of a CIS is as wide as the object under inspection (up to 4 m). The image is produced by 1 :1 optics. The pixel size ranges from 11 µm to 127 µm.

What are the advantages of a CIS compared to a conventional line scan camera?

  • Simple to mount, no large standoff distance is necessary
  • Simple to adjust, no multi camera alignment problems
  • Constant picture angle over the total reading width
  • No distortion by the lens
  • Clearly sharper images

What are the advantages of a conventional line scan camera compared to a CIS?

  • Bigger Depth of Field (DoF)
  • Lower weight

Why can’t I buy an industrial CIS at the price of a scanner?

  • Higher image quality
  • Higher line rate due to more complicated electronics
  • Large reading distance (10 mm instead of 0.3 mm) due to more complex lenses
  • Robust design (Solid metal housing
  • Standardized frame grabber interface

How do I control the exposure of a CIS?

By an internal or external light source controlled either via the Camera Link serial port or an internal timer in the CIS scanner.

The sharper imaging of a CIS in contrast to a conventional camera may cause interferences if periodical patterns are inspected. What can I do?

The option “multiple flashing” surpresses interferences as far as possible.

Which distance between object and sensor is possible?

The industrial CIS allows a maximum working distance of up to 11 mm. The nominal working distance is set at the factory.

What is the Depth of Field of a CIS?

As a rule, 1–2mm, depending on the standoff distance and the application.

Which is the local resolution of a CIS?

Tichawa Vision offers CIS units from 25 dpi (1.016 mm pixel pitch) up to 2400 dpi (10.85 µm pixel pitch).

Which local resolution do I need for my application?

This very much depends on the processing to be done. Generally speaking, the smallest object to be recognized should at least be 2-5 pixels across. Typical interpolation tasks such as gravity determination, etc. can be done very much finer than the pixel grid.

Which line rate does my application require?

The line rate is the result of the object transport speed divided by pixel size.

For example: The pixel size of a 200 dpi sensor is 127 µm. At a feed speed of 1 m/sec the line rate required is 1m/sec / 0.000127 m = 8000 Hz = 8 kHz. The sensor should be operated at a line rate of 8 kHz.

What kind of illumination is best for my requirement?

One-sided reflective light is sufficient for flat structures (print).
Textured materials require double-sided reflective light (in feeding direction in front and behind the sensor).
Transparent and printed materials often require transmissive light.
Special applications (e.g. scanning of security papers) often require a combination of reflective and transmissive light. CIS supports multiplex operation up to 6 light sources.

See also the “Illumination guide”.

Which colour of lighting is best for my application?

Red light is usually sufficient for simple B/W applications.

How does the PRNU of the CIS compare to a conventional line scan camera under uniform lighting?

Under ideal conditions a conventional line scan camera shows a typical PRNU of 10 %. But in real conditions the amplitude falls at the edge of the image area due to the wide angle of view. Correction is often used to reduce this. Typical uncorrected PRNU for a CIS is around 30 %, but the internal correction supplied can reduce this to 1-2 %.

What is the CIS bit depth?

Internal calculation in the CIS are carried out at 10 bits. After correction, 8 bits are read-out through the CameraLink port.

Is there a difference in sharpness of an image taken by a CIS compared to a conventional line scan camera?

The sharpness of a line scan camera is mostly limited by the lens. Typically, the lens aperture is run at or near its maximum and black/white transitions usually span 3-5 pixels. The transition width of a CIS is typically 1-2 pixels.

What is the spectral sensitivity of a CIS like?

As in with CCD or CMOS cameras the pixels of a CIS are made of silicon with high visible sensitivity and response extending into the near infrared.

Does the CIS sensor have gaps?

At the joints of the lined-up sensor chips to about 300 dpi, the disturbance is usually negligible since it is less than ½ pixel. With overlapping sensor chips joints will not occur. Its double pixel in the overlap region can be deleted with a correction. All in all the distortion observed with a CIS is lower than the distortion of a lens and easier to correct because the geometry is very linear.

What do I have to take care of when I install a CIS?

A CIS is much closer to the object under inspection than a conventional camera. Therefore:

  • Provide protection to avoid having objects jam up against the sensor or fall on it.
  • Take precautions against ESD, especially in applications with glass and fast running synthetic fabrics as well as with all other materials which generate static electricity.
  • CIS with internal light source is classified to the lamp safety standard IEC 62471 in the risk group RG 2. Follow the relevant regulations.