Signametrics Corporation SMU2060, Руководство оператора

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While DMMReadMeasurement(0, rd(i)) = No ‘ wait for readings to be ready, and pick them
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4.14.4 External Trigger and Sync Handshake
The Trigger and Sync signals, in conjunction with their commands provide means to synchronize
operation, yealding a fast and accurate handshake with external devices. These devices may include
switching modules, or a Component handler in a manufacturing environment. The DMM initiates an
operation by generating a short Sync pulse to the Handler (
DMMOutputSync() ), causing it to go move
to its first position (an off position, or a component). When it is in position, the Handler acknowledges by
sending the DMM a Trigger pulse. The DMM waits for this pulse (
DMMWaitForTrigger() ), and
responds to it by making a measurement. The DMM generates the next Sync pulse, and this process
repeats for as many steps as required.
Figure 4-15. Interface timing diagram of a Component Handler interface and a DMM. The DMM is the
master, or the controlling device.
4.15 Time and Frequency 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 3 times the selected range.
4.15.1 Threshold DAC (SMU2064)
All timing measurements utilize the AC Voltage path, which is AC coupled. You need to select the
appropriate ACV range prior to using the various frequency and timing measurement functions. The
SMU2064 hase a novel feature to accurately make these measurements for all waveforms. Unlike
symmetrical waveforms such as a sine wave and square wave, non-symmetrical waves may produce a
non-zero DC bias at the frequency counter’s comparator input. Other DMM’s have the comparator hard-
wired to the zero crossing, and therefore cannot handle asymmetrical wave such as a very low duty cycle
signal. The SMU2064 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 Median Value measurements and Threshold DAC settings.
The best setting of the Threshold DAC is based on the AC Median Value and Peak-to-Peak measurement
described earlier. For example 5 V logic level signal with 10% duty cycle. This input has a median value
of 2 V. A 90% duty cycle signal will have a –2 V median value. Setting the Threshold DAC to the
appropriate median value will result in reliable and accurate timing measurements in each case.
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