Horizontal scan rate

Horizontal scan rate,or horizontal frequency, usually expressed inkilohertz,is the number of times per second that araster-scanvideo system transmits or displays a complete horizontal line, as opposed tovertical scan rate,the number of times per second that an entire screenful of image data is transmitted or displayed.

Cathode ray tubes

Within acathode-ray tube(CRT), the horizontal scan rate is how many times in a second that theelectron beammoves from the left side of the display to the right and back. The number of horizontal lines displayed per second can be roughly derived from this number multiplied by the vertical scan rate.

The horizontal scan frequencies of a CRT include some intervals that occur during the vertical blanking interval, so the horizontal scan rate does not directly correlate to visible display lines unless the quantity of unseen lines are also known.

The horizontal scan rate is one of the primary figures determining theresolutioncapability of a CRT, since it is determined by how quickly theelectromagnetic deflectionsystem can reverse the current flowing in the deflection coil in order to move the electron beam from one side of the display to the other. Reversing thecurrentmore quickly requires highervoltages,which require more expensive electrical components.

Inanalog televisionsystems, the horizontal frequency is between 15.625 kHz and 15.750 kHz.

Other technologies

While other display technologies such asliquid-crystal displaysdo not have the specific electrical characteristics that constrain horizontal scan rates on CRTs, there is still a horizontal scan rate characteristic in the signals that drive these displays.