Laser LS8000-3 manual Quadrature Outputs at Extremely Low Pulse Frequencies, Definitions

LaserSpeed 8000-3 Instruction Handbook

Interfacing with the LS8000-3

Quadrature Outputs at Extremely Low Pulse Frequencies

Note: This section only applies to the pulse outputs—the length and speed available over the RS-232, RS-422, and Ethernet ports are not affected.

The LS8000-3 uses a DDS (Direct Digital Synthesis) circuit to generate the quadrature outputs. Due to the nature of DDS technology, the frequency output is not continuously variable, but occurs in steps of about 0.015Hz. Normally, relative to the output frequency, this step size is so small that it is impossible to measure. However, if both a very low speed is measured, and a very low pulse

resolution is used, the		8		Pulse Frequency Error vs. Pulse Frequency
pulse output		7
frequency will be
frequency low enough	%	6
for the step size to	/
	Envelope	5
cause noticeable
errors in	Error	4
measurement. The	Frequency
following graph shows		3
the envelope of the	Pulse	2
pulse output
frequency error as the		1
pulse output		0
frequency approaches
		10-2	10-1	100	101	102	103

zero.

Pulse Frequency / Hz

The error decreases very rapidly as the frequency increases, becoming insignificant at pulse output frequencies higher than 15Hz. For this reason, the pulse output resolution should be set such that the minimum production line speed produces a pulse output frequency higher than 15Hz.

The following equations can be used to calculate the minimum pulse output resolution.

Definitions:

R = Minimum Recommended Pulse Output Resolution

X = Minimum Production Linespeed

Part No. 93463 / Drawing No. 0921-01561 Page 41 of 221 Revision A (Sep 2007)