Operator`s manual

The dThresh value is in base units, and m
ust be within the selected measurement range. For example,
while in the 240 mV range, dThresh must be within -0.24 and +0.24. In the 24k, range it must be set
between 0.0 and 24000.0.
Use the DMMReady to monitor completion of this operation. When ready, read up-to the above buffer
size, using DMMReadBuffer or DMMReadBufferStr functions. Once DMMReady returns TRUE, it
should not be used again prior to reading the buffer, since it initializes the buffer for reading when it
detects a ready condition.
Read Interval must be set between 0 (default) and 65ms. Aperture must be set between 160ms and 2.5us.
The value of iPostSamples must be set between 1 and the buffer size. The buffer size is 80 for Apertures
of 160ms to 1.4ms, and 120 for Apertures in the range of 2.5µs to 625us. The highest Aperture allowed
for this operation is 160ms. Aperture and Read Interval are set using the DMMSetAperture and
DMMSetReadInteval functions, respectively.
Figure 4-14. Analog Threshold Trigger operation with Positive Edge and Sync enabled.
4.14.3 Software Initiated Triggered Operations
There are several software trigger functions. They can commend the DMM to make a predefined number
of readings, with a specified number of settling readings. These include DMMSetBuffTrigRead,
DMMSetTrigRead, DMMTrigger, DMMBurstRead and DMMBurstBuffRead. Read about these
functions in the Windows Command Language section (5.6) for details.
4.14.3.1 Burst Read Operation
In response to the DMMBurstRead(nDmm, iSettle, iSamples) command, the DMM enters a tight
measurement loop, where it samples the input and returns measurements to the calling S/W. For each
measurement sent, it takes iSettle + 1 sample, sending only the last sample. A total of iSamples * (iSettle
+ 1) are taken by the DMM, and iSamples are sent back. With the Read Interval set to 0, the total time
per measurement is (iSettle + 1) * Aperture time plus the time it takes to transmit the data back. The last is
equal to 132µ for Aperture times greater than 625µs, and 88µs for other apertures. For instance, if iSettle
is set to 3, and the Aperture is set to 10ms, the total time per sample will be 4 * 10ms + 132us =
40.132ms. iSettle may be set to a value of 0 to 250. The total number of measurements, iSamples, must be
between 1 and 60,000. Setting the Read Interval can help with fine tuning of the sampling timing. Failing
to read the measurements at the rate they become available, or not reading all of the readings will result in
communication overrun. Aperture must be set to 160ms or lower value. The Sync output line maybe
turned on to synchronize external devices (DMMSetSync(0, Yes, 1)).
To retrieve the readings, following the issue of the DMMBurstRead command, use the
DMMReadMeasurement. For proper operation, you must retrieve iSamples readings.
i = DMMBurstRead(0, 2, 1000) ‘Take two settling readings per sample, make 1000 measurements
For i = 0 To 1000 – 1 'Tight read loop, need to get them as fast as they come. Read 1000
49 Signametrics
W
hile DMMReadMeasurement(0, rd(i)) = No ‘ wait for readings to be ready, and pick them