Operator`s manual
47 Signametrics
4.13.3.4 Triggered Burst Capture
This function is similar to the Burst Read operation above. In response to the DMMSetTrigRead (nDmm, iSettle,
iSamples, iEdge) command, the DMM enters a tight loop, where it responds to a trigger edge. On each of these
edges triggers the DMM to capture and send back a measurement. The total of trigger edges and measurement being
equal to iSamples. For each hardware trigger edge, the DMM takes iSettle + 1 measurements, sending the last one.
The S/W must keep up and read those samples as they come. iSettle may be set to a value between 0 to 250. The
total number of measurements, iSamples, must be between 1 and 30,000. Setting the Read Interval can help with
defining the sampling timing. Use the DMMReady() function to monitor completion. Aperture time must not
exceed 160ms. The amount of time it takes the DMM to transmit the data back depends on the selected Aperture. It
is about 132µ for Aperture times greater than 625µs, and 88µs for other apertures.
i = DMMSetTrigRead(0, 2, 500, LEADING) ‘Two setteling readings per sample, 500 measurements
For i = 0 To 500 – 1 'Tight read loop, need to get them as fast as they come. Read 500
While DMMReadMeasurement(0, rd(i)) = No ‘ wait for readings to be ready, and pick them
Wend
Next
4.14 Frequency and Time Measurements
While the maximum RMS reading is limited to the set range, you can use most of the timing functions even if the
RMS voltage reading indicates over range. This is true as long as the input peak-to-peak value does not exceed 6
times the selected range.
4.14.1 Threshold DAC
All timing measurements utilize the AC Voltage path, which is AC coupled. You need to select the appropriate
64 have a novel
s such as a sine
wav may produce a non-zero DC bias at the frequency counter’s
t handle
tings.
urement described
y
cycl ting the Threshold DAC to the appropriate median value will result
ACV range prior to using the various frequency and timing measurement functions. The SM20
feat or all waveforms. Unlike symmetrical waveformure to accurately make these measurements f
e and square wave, non-symmetrical waves
comparator input. Other DMM’s have the comparator hard-wired to the zero crossing, and therefore canno
asymmetrical wave such as a very low duty cycle signal. The SM2064 have a bipolar, variable Threshold DAC that
enables these DMM’s to performance of these measurements. Functions affected by the Threshold DAC include
frequency, period, pulse-width, duty-cycle and the Totalizer/Event Counter.
The Threshold DAC has 12 bits of resolution. Depending on the selected ACV range, this bipolar DAC can be set
from a few mV to several hundred volts, positive or negative. See the Specifications sections for the limits of AC
M dian Value measurements and Threshold DAC sete
The best setting of the Threshold DAC is based on the AC Median Value and Peak-to-Peak meas
earl 10% duty cycle. This input has a median value of 2 V. A 90% dutier. For example 5 V logic level signal with
e signal will have a –2 V median value. Set
in reliable and accurate timing measurements in each case.
Figure 4-13. AC coupled timing measurements with Threshold DAC.