Signametrics Corporation SM4020, Руководство оператора

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SCANTriggerOutState(iScan, Enabled, PosEdge) ‘ Set trigger output to Positive edge.
iReadings = 10 ‘ Total number of measurements to take
DMMSetTrigRead(iDmm, 4, iReadings, NegEdge) ‘ Total of 10 readings and 4 settling readings each
SCANAutoScan(iScan, iSteps) ‘ Start auto scan
For I = 0 to iReadings -1 ‘ read measurements as they come
While DMMReadTrigVal(iDmm, reading) = NO ‘ wait for each reading and store it
DoEvents
Wend
Next
SCANOpenAllChannels(iScan)
‘ Good idea to open all channels when done
Figure 4-13. Triggered reading process and timing of SM4042 Scanner and SM2044 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 SM2040 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-Act (nSe 1) / (read. per
sec.)
4.5 Single Ended application Example
4.5.1 Point to Point Configuration
This may not be obvious, but the SM4040 and SM4042 can be used for single ended applications.
Taking advantage of the Universal mode, a point to point switching can be implemented. Such
application includes loaded board test commonly used by MDAs. The 40 differntial inputs to the
multiplexer become 80 independent lines (Ch1Hi, Ch1,Lo, Ch2Hi, Ch2Lo, ... CH40Hi, Ch40Lo)
which can be connected to one of the four busses, A, B, C and D. These in turn can be connected to
an instuments such as the SM2044 DMM. Further, it is also possible to configure it in such a way that
the selected line can may be connected to either the positive or the negative terminal of the DMM.
Using multiple SM4042 a high point test system can be constructed. In the following example, the
Vlow of the DMM is connected to the Bhi and the Dlo line of the SM4042. The Vhigh of the DMM
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