PLUS+1 User Forum

General Discussion => Tips & tricks => Topic started by: Nilla on March 08, 2017, 10:44:03 AM

Title: Displays - Noise on video and how the sync works
Post by: Nilla on March 08, 2017, 10:44:03 AM
A video signal contains embedded synchronization pulses. The image is scanned from left to right, top to bottom. The horizontal sync rate is 15.734 kHz and the vertical sync rate is 29.97 Hz. 15.734 kHz corresponds to a period time of 63.6 µs and 29.97 Hz to 33.4 ms.

A disturbance in the ns range will probably not cause more than some noise in the image, the video decoder in the display can still detect the sync pulses correctly.

A disturbance in the µs range may result in that the synchronization is lost for one or more lines. The video decoder can tolerate the absence of synchronization for a few lines (~dead reckoning).

The video decoder will fail to keep track of the video signal position when the disturbance persists over a large number of lines or perhaps even frames. This instigate the need to re-synchronize the video decoding hardware and software. No video image can be showed while this happens.

When any of the issues above occurs, activation/deactivation of an inductive load may be at fault (or may be the root cause), e.g. a solenoid, large relay or electric motor. Inductive loads will send out large voltage spikes if the proper filtering is not used. It is not necessarily only the wire that goes to the inductive load that is affected. A voltage spike on one cable could be powerful enough to induce a disturbance on adjacent cables.

See attached pictures from

It’s good to measure the video signal on the machine with an oscilloscope. Follow the procedure below:
The best is of course to identify and address the origin of the disturbance to prevent from any new issues in the future.

Best regards
PLUS+1 Helpdesk team