Keithley 194 Instruction Manual page 86

OPERATION
3.22.2 Long Term Measurements
Although the Model 194 is primarily designed for high
sampling rates, its large measurement buffer makes it
suitable for any application requiring a large number of
samples--even on a long term basis.
Long term drift analysis of power supplies is one area
where such measurements may be required. The Model
194 could be programmed to sample the power supply
voltage at specific intervals. Once the measurement cycle
is completed, the peak-to-peak variations as well as the
long-term average power supply voltage could then be easi-
ly obtained with the Model 194 mathematical functions.
For example, assume you desire to monitor the output
voltage of a power supply at one second intervals. You
would then program the instrument for this interval by
entering information with the RATE key. The number of
samples to be programmed would then depend on the
duration of the test. With a one-second interval, a total of
7,200 samples would be required for a two-hour measure-
ment period.
3.22.3 Digital Storage Oscilloscope
Oscilloscope analysis of recurrent or periodic waveforms
is fairly routine since the scope can be triggered repeated-
ly to generate the required trace. Transient waveforms are
another story, however, as it is generally difficult, if not
impossible, to view such waveforms on an ordinary
oscilloscope. The Model 194, however, can give you digital
storage oscilloscope capabilities when used with an exter-
nal display device such as a plotter, CRT, or a basic
oscilloscope.
Consider the transient waveform shown in Figure 3-26.
When the Model 194 is performing a measurement se-
quence, it will measure all or part of the waveform, as
determined by the sampling window. The relative size of
this sampling window depends on the programmed rate
and samples, as well as such trigger parameters as delay,
slope, and level. Since the measured waveform is transient
in nature, careful selection of these parameters is necessary
to ensure proper triggering and measurement.
Figure 3-26. Transient Waveform
Once the waveform has been digitized and stored in the
buffer, the XY mode can be used to graph the data. 'Three
basic graphing modes arc available: CRT. oscilloscope, and
plotter.
The XY analog output is used to drive the graphing device
regardless of the plot mode selected. Figure 3-27 shows
typical connections for the oscilloscope and plotter modes.
With the oscilloscope mode in (A), the Y output is used
drive the vertical input of the scope, while the % output
is connected to the external trigger input. With the plotter
in (B), the X and Y outputs drive the X and Y inputs of
the plotter, while the 1. output provides a pen up signal
for the plotter.
3-47