Operator`s manual

Figure 4-13. Triggered reading process and timing of SMX4032 Scanner and SMX2044 DMMs.
Unlike the previous example, DMMSetBuffTrigRead() is not time critical since the DMM saves all
measurements to it’s on-board buffer, which is read after the scan is complete.
SCANTriggerOutState(iScan, Enabled, PosEdge) ‘ Set trigger output to Positive edge.
iReadings = 50 ‘ Total number of measurements to take
DMMSetBuffTrigRead(iDmm, 4, iReadings, NegEdge) ‘ Use 4 settling readings each
SCANAutoScan(iScan, iSteps) ‘ Set off AutoScan
While DMMReady(iDmm) = NO ‘ wait for the DMM to indicate capture
Wend ‘ completion of iReadings (available In buffer)
For I = 0 to iReadings -1 ‘ read values stored in the buffer
DMMReadBuffer(iDmm, Buffer(I) ) ‘ Store each reading
Next
SCANOpenAllChannels(iScan) ‘ Good idea to open all channels when done
While SCANReady(iScan) = NO ‘ Since AutoScan is a polled operation,
DoEvents ' Make sure Scanner is ready
Wend
There are several SMX2040 family commands to considered for this operation:
DMMSetTrigRead(), DMMSetBuffTrigRead(), DMMReadTrigVal(), DMMReady(),
DMMReadBuffer() and DMMReadBufferStr(). Do not forget to open all channels at the end of the
scan, using SCANOpenAllChannels().
Referring to figure 4.13, it is clear that the total time the DMM takes reading must be kept shorter
than t-Delay (t-Step – t-Actuation), for completion of the measurements prior to the selection of the
next channel. That means that t-Step must be greater than t-Actuation + (nSettling + 1) / (read. per
sec.)
4.5 Single Ended Applications
4.5.1 Point to Point Operation
This may not be obvious, but the SMX4030 and SMX4032 modules can be used for single ended
applications. Taking advantage of the Universal mode, which allows any relay to be closed, a point to
point switching can be implemented. Such application includes loaded board test commonly used by
MDAs. The 32 differential inputs to the multiplexer become 64 independent lines (Ch1Hi, Ch1Lo,
Ch2Hi, Ch2Lo, ... CH32Hi, Ch32Lo…) which can be connected to one of the four busses, A, B, C
and D. These in turn can be connected to instruments such as the SMX2064 DMM. Further, it is also
possible to configure it in such a way that the selected line can be connected to either the positive or
the negative terminal of a DMM. Using multiple SMX4032, a high point test system can be
constructed. In the following example, the Vlow input of the DMM is connected to both, the Bhi and
the Dlo lines of the SMX4032. The Vhigh input of the DMM is connected to both, the Ahi and Clo of
the SMX4032. The top eight lines of Figure 4-14 demonstrate a multiple SMX4032 system, where
only a single line is connected to either High or Low terminal of an SMX2044 DMM. The following
table provides the setting for a few single-ended connections to exemplify this application. The lst
three lines in the table depict a single SMX4032 usage where measurements between Ch32Lo line
and Ch1Hi line are performed. The last two lines demonstrate how to make a measurement in both
polarities between Ch1Hi line and Ch1Lo line.
27 Signametrics