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

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

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.