o an SM2060 class of DMM’s.
Figure 4-16. Trig
connection t
4.16.2 M
or two wire mea
e SM2060 DM
the scanner, or to both, the A-
us and C-Bus for 4-Wire measurements (assuming an SM4040 or SM4042 scanner). It is important to consider
ime delays exist in any measurement system. These delays are
anner’s relay actuation times, the DMM input settling and
ge
es
g
a minimum of 4 is recommended regardless of measurement rate).
Timing
2060 DMM to make triggered measurements. The triggers are generated by the
tion time. This could
he scanning. The SM2060 must be set up for triggered readings by using the
ead()
command. In the following Visual Basic® example, the SM2060 sends readings during the
s limited to 5 readings, and the DMM must continue to send all readings during the
it i
rror occurs.
o
ge)
// Set trigger output to Positive edge.
// Total number of measurements to take
readinigs and 4 settling readings
dings -1
// read values as they come
MReadMeasurement(nDmm, reading) = NO
// wait for each reading and store it
// Good idea to open all channels when done
ger interfacing
ultiplexing with the SM
surements, th
2060 DMM’s
M must be connected to the A-Bus or
F
B
system-settling time when making measurements. T
contributed by various sources. These include the sc
wiring capacitance. The latter will varies with the type of measurement. For instance, when making high value
Ohms measurements the DMM current source level could contribute significant delay due to the capacitance char
time. For example, with 1,000pf cable capacitance, the source current of the SM2064 DMM using the 33M
Ω
rang
is 0.1
µ
A which translates to 33ms (dt = C*dV/I). It is also recommended to set the appropriate number of settlin
easurements for the DMM (
m
4.16.3 Interface Commands and
The sequence requires the SM
SM4040. Start by setting the SM4040 to the desired configuration, with Trigger Output enabled and positive
polarity. Each channel selection will generate a positive pulse with duration equal to the actua
be generated by one of t
DMMSetTrigR
scan. Since it’s on board FIFO i
scan,
s important to have a tight loop that reads the measurements fast enough so that no overrun e
Refer t Figure 4-16 for proper trigger connection.
SCANTrigg
tState(nScan
bled, P
erOu
, Ena
osEd
nReadings = 100
DMMSetTrigRead(nDmm, 4, nReadings, NegEdge)
// Total of 100
nScan, nSteps)
//
Start
auto
scan
SCANAutoScan(
a
For I = 0 to nRe
while(DM
Next
SCANOpenAllChannels(nScan)
Figure 4-17. Tr gered reading p
Signametrics
52
ig
rocess and timing of SM4042 Scanner and an SM2064 DMM’s.
uffTrigRead()
is not time critical since the DMM saves all
ich is read after the scan is complete. However, this function
mited to a maximum of 64 readings per scan.
n, nSteps)
‘
Set
off
AutoScan
Unlike
the previous example,
DMMSetB
surements to it’s on-board buffer, wh
mea
li
is
SCANTriggerOutState(nScan, Enabled, PosEdge)
‘ Set trigger output to Positive edge.
nReadings = 50
‘ Total number of measurements to take
DMMSetBuffTrigRead(nDmm, 4, nReadings, NegEdge)
‘ Use 4 settling readings each
SCANAutoScan(nSca
