User manual

Operator's Manual

Averaging Waveforms

Summed Averaging

Summed Averaging is the repeated addition, with equal weight, of successive source waveform records. If a

stable trigger is available, the resulting average has a random noise component lower than that of a single-

shot record. Whenever the maximum number of sweeps is reached, the averaging process stops. In Summed

averaging, you specify the number of acquisitions to be averaged. The averaged data is updated at regular

intervals.

An even larger number of records can be accumulated simply by changing the number in the dialog. However,

the other parameters must be left unchanged or a new averaging calculation will be started. You can pause

the averaging by changing the trigger mode from NORM/AUTO to STOP. The instrument resumes averaging

when you change the trigger mode back to NORM/AUTO.

You can reset the accumulated average by pushing the CLEAR SWEEPS button or by changing an acquisition

parameter such as input gain, offset, coupling, trigger condition, timebase, or bandwidth limit. The number of

current averaged waveforms of the function, or its zoom, is shown in the acquisition status dialog. When

summed averaging is performed, the display is updated at a reduced rate to increase the averaging speed

(points and events per second).

Continuous Averaging

Continuous Averaging, the default setting, is the repeated addition, with unequal weight, of successive

source waveforms. It is particularly useful for reducing noise on signals that drift very slowly in time or

amplitude. The most recently acquired waveform has more weight than all the previously acquired ones: the

continuous average is dominated by the statistical fluctuations of the most recently acquired waveform. The

weight of ‘old' waveforms in the continuous average tends to zero (following an exponential rule) at a rate

that decreases as the weight increases.

You determine the importance of new data vs. old data by assigning a weighting factor. Continuous

averaging allows you to make adjustments to a system under test and to see the results immediately. The

formula for both summed and continuous averaging is:

new average = (new data + weight * old average)/(weight + 1)

However, by setting a "sweeps" value, you establish a fixed weight that is assigned to the old average once

the number of "sweeps" is reached. For example, for a sweeps (weight) value of 4:

sweep (no old average yet): new average = (new data +0 * old average)/(0 + 1) = new data only

sweep: new average = (new data + 1*old average)/(1 + 1) = 1/2 new data +1/2 old average

sweep: new average = (new data + 2 * old average)/(2 + 1) = 1/3 new data + 2/3 old average

sweep: new average = (new data + 3 * old average)/(3 + 1) = 1/4 new data + 3/4 old average

sweep: new average = (new data + 4 * old average)/(4 + 1) = 1/5 new data + 4/5 old average