Operator`s manual

37 Signametrics
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4.12.4 Pulse Width
User selectable positive or negative pulse widths may be measured for signal frequencies of 1 Hz to 100 kHz and
minimum pulse widths of 2 µs. The Threshold DAC feature allows measurements at a pre-defined signal level. See
Threshold DAC above for more details.
To measure pulse width, the DMM must be in the AC volts range appropriate for the input voltage. Keeping the
peak-to-peak amplitude of the measured signal below 5.75 times the set range will guarantee the signal is within the
linear region of the AC circuitry and gives the best performance.
4.12.5 Totalizer Event Couner
The Totalizer can be selected while the DMM is in the ACV mode. It is capable of counting events such as over-
voltage excursions, switch closures, decaying resonance count, etc. The active edge polarity can be set for a positive
or negative transition. A count of up to 10
9
may be accumulated. The maximum rate of accumulation is 30,000
events per second.
The Threshold DAC can be set for a negative or positive voltage value. See Threshold DAC above for more details.
Example One: To monitor and capture the AC line for positive spikes which exceed 10% of the nominal 120 V
RMS value, first select ACV 250 V range, than set the Threshold DAC to 186.7 V. This value is the peak value of
120 V RMS plus 10% (120V + 10%) X
4.12.3 Duty Cycle Measure
Duty Cycle of signals from 1 Hz to 100 kHz can be measured. The minimum positive or negative pulse wid
signal must be at least greater than 2 µs. When measuring duty cycle precisely, the voltage at which the
measurement is made is important, due to finite slew rates of the signal. With the SM2042 and SM2044, the
Threshold voltage can be set for precise control of the level at which duty cycle is measured. For best measurement
results, set the Threshold DAC to the Median value. This is particularly important for signals with low duty-cycle
and small amplitude relative to the selected scale.
2
). Enable the Totalizer and read it periodically to get the number of
times this value was exceeded.
Example Two: Defects in coils, inductors, or transformers can be manifested as an increased decay, or greatly
attenuated resonance when stimulated with a charged capacitor. The Totalizer function can be utilized to count
transitions above a preset Threshold voltage as in the Figure 4-12 below.
Figu ying resonance with preset threshold.
Two digital-to-analog converters (DACs) are used for the source functions, a 12-bit DAC, and a Trim DAC. The
it DAC only.
re 4-12. Measuring inductor Q by counting transitions of deca
4.13 Sourcing Functions (SM2044)
The SM2044 adds a number of sourcing functions, giving greater versatility for a variety of applications. All of the
available sources, VDC, VAC, IDC, are isolated (floating with respect to the PC chassis). This allows sourcing with
a significant common mode voltage as well as the ability to connect several SM2044 units in parallel for increased
DC current, or in series for increased DC voltage.
last augments the 12-bit DAC to form a 16 bit composite DAC and adds an additional 8 bits of resolution. For
functions requiring high precision, use both DACs by selecting the ClosedLoop mode, otherwise only the 12-bit
DAC is utilized. DCI source is limited to the 12-b