Sigma LBA-710, LBA-714PC, LBA-300, LBA-712, LBA-708, LBA-500PC, LBA-700 Frame Averaging, Frame Summing

for the Standard Deviation,

			n			2
			∑(S −		)
				s
		σ =	n=1
			n − 1
Where:	=	std. deviation.
σ
n	=	number of samples.
Σ(S - s )² =		sum of the square of the differences between
		the mean and each sample.

The Maximum and Minimum are just the largest and smallest values encountered in the samples.

6.24 Frame Averaging

The signal to noise ratio of the digitized data can be improved by using Frame Averaging. The amount of the improvement is roughly the square root of the number of frames being averaged. The LBA-PC can average a maximum of 256 frames for at best a 16 times improvement of the signal to noise ratio. The amount of improvement is also limited by the noise content of your camera and our digitizer system. In general you will begin to receive diminishing returns when you average more frames than the square of the number of noise counts. For CCD cameras the noise is about 4-5 counts, so averaging more than 16 to 25 frames will be of little benefit.

Pulse to pulse variations for a pulsed laser will be reduced by a like amount.

When Frame Averaging is enabled, the display will update with the averaged results only after all frames have been received. Any calculations will similarly be performed only after all frames have been received.

Notice: When Frame Averaging is enabled and you click on Stop!, the LBA will immediately abort the collection of frames for averaging and will display the last completed set of averaged data. Any frames that were in the process of being averaged are discarded, thus when you again click Start! a totally new averaging process is begun.

Notice: Do Not use Frame Averaging if your beam suffers from poor pointing stability, and you want to make accurate beam width measurements. Instead, enable statistics and find the mean beam width by using results averaging. This is independent of centroid position.

6.25 Frame Summing

You can use Frame Summing to observe the cumulative effect of a pulsed laser. The LBA-PC can sum a maximum of 256 frames. Be careful that your pulse rate is not greater than the LBA and Camera system can keep up with, and that the total energy doesn’t exceed the available dynamic range. Note: You may want to use block mode to insure that you do not miss any pulses.

Frame summing will cause fixed pattern noise to increase in proportion to the number of frames summed, while temporal noise will increase only as the square root of the number of frames being summed. Thus some improvement in the signal to noise ratio will be realized. To further improve the signal to noise ratio, try using Frame Summing together with Frame Averaging.

Operator’s Manual 144 LBA-PC