Common of particular sign elements

Generally, you solely need to analyze these sign elements that meet sure standards or happen at sure occasions inside an acquisition. This isn’t too troublesome for a single acquisition, however what if you wish to acquire the typical of these chosen measurement occasions? Right here is the place seemingly unrelated options of the oscilloscope can work collectively to get the specified information.

Take into account an utility the place a tool produces periodic RF pulse bursts, as proven in Determine 1.

Determine 1 The system below take a look at produces periodic RF pulse bursts; the take a look at purpose is to accumulate and common bursts with particular amplitudes. Supply Arthur Pini

The purpose of the take a look at is to accumulate and common solely these bursts with a particular amplitude. On this case, these with a nominal worth of 300 millivolts (mV) peak-to-peak. This desired measurement may be completed utilizing the oscilloscope’s Cross/Fail testing functionality to qualify the sign. Cross/Fail testing permits the consumer to check the waveform based mostly on parametric measurements, like amplitude, and go or fail the measured waveform based mostly on it assembly preset limits. Alternatively, it may be examined by evaluating the waveform to a masks template to find out if the waveform is inside or exterior of the masks. Primarily based on the take a look at outcomes, many actions may be taken, from stopping the acquisition, storing the acquired waveform to reminiscence or file, sounding an audible alarm, or emitting a pulse.

Selective averaging makes use of Cross/Fail testing to isolate the specified pulse bursts based mostly on their amplitude or conformance to a masks template. Alerts assembly the Cross/Fail standards are saved in inside reminiscence. The averager is about to make use of that storage reminiscence as its supply in order that certified alerts transferred to the reminiscence are added to the typical.

Organising Cross/Fail testing

Testing is predicated on the peak-to-peak amplitude, which makes use of measurement parameter P1. The measurement setup accepts or passes a pulse burst having a nominal peak-to-peak amplitude of 300 mV inside a spread of ±50 mV of nominal. The take a look at limits are arrange in take a look at situation Q1 (Determine 2).

Determine 2 The preliminary setup to seize and common solely pulses with amplitudes of 300 ± 50 mV. Supply: Arthur Pini

The oscilloscope’s timebase is about to seize particular person pulse bursts, on this case, 100 ns per division. That is vital as solely particular person bursts needs to be added to the typical. A single burst has been acquired, and its peak-to-peak amplitude is 334 mV, as learn in parameter P1. The Cross/Fail take a look at setup Q1 exams for the sign amplitude inside ±50 mV of the nominal 300 mV amplitude. These limits are user-adjustable to accumulate pulse bursts of any amplitude.

A single acquisition is made, buying a 338 mV pulse, which seems within the high show grid. This meets the Cross/Fail take a look at standards, and the sign is saved in reminiscence M1 (Determine 3).

Determine 3 Buying a sign that meets the acceptance standards provides a duplicate of the sign in reminiscence M1 (middle grid) and provides it to the averager contents (decrease grid). Supply: Arthur Pini

The reminiscence contents are added to the typical, displaying a waveform depend of 1. The Actions tab of the Cross/Fail setup reveals that if the acquired sign passes the acceptance standards, it’s transferred into reminiscence. The waveform retailer operation (i.e., what hint is saved in what reminiscence) is about up individually within the Save Waveform operation below the File pulldown menu.

What occurs if the acquired pulse doesn’t meet the take a look at standards? That is proven in Determine 4.

Determine 4 Buying a 247 mV burst ends in a failed Q1 situation. On this case, the sign will not be saved to M1 and isn’t added to the typical. Supply Arthur Pini

The acquired waveform has a peak-to-peak amplitude of 247 mV, exterior the take a look at restrict. This ends in a failure of the Q1 take a look at (proven in pink). The take a look at motion doesn’t happen, and the low amplitude sign will not be added to the typical.

Utilizing masks templates

Selective averaging may also be based mostly on masks testing. Masks may be created based mostly on an acquired waveform, or customized masks may be created utilizing software program utilities from the oscilloscope producer and downloaded to the oscilloscope. This instance makes use of a masks based mostly on the acquired sign (Determine 5).

Determine 5 A masks, based mostly on the nominal amplitude sign, is created within the oscilloscope. The acquired sign passes if all waveform samples are inside the masks. Supply Arthur Pini

The masks is created by including incremental variations each horizontally and vertically concerning the supply waveform. All factors should be contained in the masks for the acquired sign to go. As within the earlier case, if the sign passes, it’s saved in reminiscence and added to the typical (Determine 6).

Determine 6 If the acquired sign is absolutely contained in the masks, it’s transferred to reminiscence M1 and added to the typical. Supply Arthur Pini

If the acquired sign has factors exterior the masks, the take a look at fails, and the sign will not be transferred to reminiscence or the typical (Determine 7).

Determine 7 An instance of a masks take a look at failure with the circled factors exterior the masks. This waveform will not be added to the typical. Supply Arthur Pini

Selective averaging with a gating sign

This system may also be utilized to alerts on a multiplexed bus with a gating sign, comparable to a chip choose, accessible (Determine 8). 

Determine 8 Cross/Fail testing may be employed to pick out solely these alerts which might be time-coincident with a gating sign, comparable to a chip choose sign. Supply: Arthur Pini

The gating sign or chip choose is acquired on a separate acquisition channel. Within the instance, channel 3 (C3) was used. The gating sign is constructive when the specified sign is obtainable. So as to add solely these alerts that coincide with the gating sign, go/fail testing verifies the presence of a constructive gating sign. Testing that the utmost worth of C3 is bigger than 100 mV verifies that the gate sign is in a excessive state, and the take a look at is handed. The oscilloscope is about to retailer C1 in reminiscence M1 below a handed situation, which is added to the typical (Determine 9).

Determine 9 The common based mostly on waveforms coincident with the gate constructive gate sign state. Supply: Arthur Pini

Isolating take a look at alerts

If the segments of the analyzed sign are shut collectively and can’t be separated utilizing the usual timebase (1,2,5 step) scales, a horizontal (zoom) growth of the acquired sign can be utilized to pick out the specified sign phase half. The variable zoom scale supplies very high quality horizontal steps. The zoom hint can be utilized as a substitute of the acquired channel, and the typical supply is the zoom hint.

Selective averaging

Selective averaging, based mostly on Cross/Fail testing, is an instance of linked options in an oscilloscope that complement one another and provide the consumer a broader vary of measurements. Averaging was the chosen evaluation software, but it surely may have been changed with the quick Fourier rework (FFT) or a histogram. The oscilloscope used on this instance was a Teledyne LeCroy HDO 6034B.

Arthur Pini is a technical help specialist and electrical engineer with over 50 years of expertise in electronics take a look at and measurement.

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