Download Feature Focus: Mask Testing

Feature Focus: Mask Testing
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About Mask Testing
Digital oscilloscope mask testing uses a math channel to compare, point-bypoint, a captured waveform to a mask consisting of an upper waveform limit and
a lower waveform limit. The captured waveform ‘passes’ if each point of the
captured waveform falls in between the upper and lower limits. Similarly, a
captured waveform ‘fails’ if a point extends above the upper limit or falls below
the lower limit.
Mask testing is sometimes also referred to as “pass/fail” or “go/no go” testing.
Mask Testing Applications
Oscilloscope mask testing can be used in any testing environment; however, it is
commonly used in manufacturing environments and for applications requiring
continuous waveform monitoring.
In a manufacturing environment, users want to compare the output of a newly
manufactured device to the output of a “golden device” or a “known good device”
(KGD). If the output from the new device falls in between the upper and lower
masks, the device passes. If the output falls outside the upper and lower masks,
then adjustments are made to the new device in an attempt to bring it into spec.
With continuous waveform monitoring applications, an oscilloscope is used to
continuously monitor a waveform for quality purposes. If the captured waveform
completely falls inside the allowed range, then the oscilloscope generates an
output signal that signifies that the waveform is OK.
ZTEC Mask Testing
ZTEC’s modular oscilloscopes have a number of advanced features for mask
testing:
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Real-time simultaneous mask testing on up to four input channels
Automatic mask generation by applying vertical and horizontal offsets to a
captured waveform
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Gated mask testing where the mask is only applied to a portion of the
captured waveform (gating can be defined by time, by number of points,
by cursor location, and by frequency (with FFT testing))
Acquisition automatically stops after a pre-defined number of failures
A variable-width output pulse can be generated after every waveform that
passes the mask test
Continuous monitoring of the number of acquisitions and the number of
failures
Setting up a Mask Test:
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First, acquire a waveform that you want to use as your golden waveform. This
waveform will serve as the basis of your upper and lower mask limits. Make sure
the waveform V/div and t/div settings are the same as you will use when
performing the mask testing.
Golden Waveform
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Define one or more of the instrument’s math channels to be used for mask
testing. This includes defining which of the reference channels will store the
upper mask and which reference channel will store the lower mask. In the screen
shot below we see that our lower waveform mask is saved in the second
reference channel (REF2) and the upper waveform mask is in REF1.
The instrument can also be configured to automatically stop acquiring after a
user-defined number of failures. In this example, we show that the instrument is
setup to automatically stop after the 5th failure.
Calc Channel Setup
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Once the math channel has been properly setup, define the allowable vertical
(voltage) and horizontal (time) offsets for the upper and lower masks. In this
example we have generated masks that are offset +/- 20mV vertically from the
captured waveform, and offset +/- 50us horizontally from the captured waveform.
Also note that we are not gating this mask test. That is, the entire waveform is
analyzed when comparing the captured waveform to upper and lower mask
waveforms.
Mask Setup
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Last, if desired, the user can set the output on the oscilloscope to generate a
variable-width pulse with every acquired waveform that passes the mask test. In
this example the output is set to output a 1ms pulse after every successful mask
test.
Limit Test Setup
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Oscilloscope Overview