53
Signametrics
hile DMMReady(nDmm) = NO
‘ wait for the DMM to indicate completion
while(DMMReadBuffer(nDmm, reading(I))
‘ Store each reading
Since AutoScan is a polled operation,
ure 4.17, the total time it takes the DMM make a reading must be set to be shorter
an t-Delay, for completion of the measurements prior to the selection of the next channel.
J,
e DMM has means for both, entering and measuring the reference (cold) junction
o
o
perature units. The cold
junc
iplex the thermocouples, and the
SM4
eing utilized to connect the thermocouples,
DMMReadCJTemp()
should be used
he
ng data
ready to be read. A short (about 100
µ
s) negative pulse is issued for each measurement, with the
ositive edge indicating data is ready. The Trigger output is selected by the third parameter (
iTrigOut
) of
e
DMM
lse can be set to be output to any of the following lines.
iTrig
W
Wend
For I = 0 to nReadings -1
‘ read values stored in the buffer
Next
SCANOpenAllChannels(nScan)
‘ Good idea to open all channels when done
While SCANReady(nScan) = NO
‘
DoEvents
'
Make
sure
Scanner
is
ready
Wend
There are several SM2060 family commands to be considered for this operation:
DMMSetTrigRead()
,
DMMSetBuffTrigRead()
,
DMMReadMeasurement()
,
DMMReady()
,
DMMReadBuffer()
and
DMMReadBufferStr()
.
Referring to fig
th
4.17 Measuring Temperature with Thermocouples
The SM2060 series of Digital Multimeters have built in linearization for eight thermocouple types including B, E,
, N, R, S and T. In addition th
K
temperature. The
DMMSetTemperatureUnits()
selects between C and F. Once selected, all subsequent
temperature functions should consider the set temperature units.
DMMSetTCType()
selects the type of
thermocouple being measured. It can be used as frequently as needed when measuring several types. Prior to
measuring a Thermocouple it is important to set the reference, or cold junction temperature. This can be done as
often as necessary as to keep track of variations in this temperature. Once set, all subsequent thermocouple
measurements will use and compensate for this temperature. One way to set this temperature is to simply pass it to
the DMM using the
DMMSetCJTemp()
.
Make sure to set it to the currently set tem
tion temperature range is 0
o
C to 50
o
C. If using the SM4042 or SM4040 to mult
0T screw terminal block is b
to measure the cold junction. Make sure to select and connect the “D” to the “A” bus of the SM4000 switching. The
third method of measuring and entering the cold junction temperature is by measuring a user provided sensor.
Provided this sensor have an output between –3.3V and +3.3V, and it can be characterize by the equation used by
the
DMMReadCJTemp();
t
cj
= b + (V
cjs
– a) / m, the parameters can be set using
DMMSetSensorParams()
. V
cjs
is
the sensor generated voltage, a, b and m are the coefficients which are entered using
DMMSetSensorParams()
and
t
cj
the cold junction temperature. Once set, use
DMMReqadCJTemp()
to measure the sensor temperature.
4.18 Using the PXI bus Trigger Facilities (SMX2064)
The
designed to interface to the PXI J2 Triggers. That includes the
SMX2064 PXI Digital Multimeters is
PXI_TRIG0 through PXI_TRIG6 and PXI_STAR trigger. The trigger to the DMM is a Wire-Ored function of t
external trigger from the DIN-7 connector, and the PXI_TRIG input. The data ready signal from the SMX2064 can
be selected to drive PXI_TRIG1 through PXI_TRIG6 or the PXI_STAR trigger. The
DMMSetPXITrigger()
function is used to select the input and output trigger.
4.18.1 Selecting PXI Trigger Outputs
The DMM issues a Data Ready pulse each time the A/D is done making a measurement, indicati
is
p
th
setPXITrigger()
function. The trigger pu
Out
Trigger Output Routing
0
Disables trigger output
0 0
0 0 1
PXI_TRIG1
0 1 0
PXI_TRIG2
0 1 1
PXI_TRIG3
1 0 0
PXI_TRIG4
1 0 1
PXI_TRIG5
1 1 0
PXI_TRIG6
1 1 1
PXI_STAR
