Temperature measurement command sequence – VXI VT1422A User Manual
Page 176
174 Advanced Programming with the VT1529B
Temperature
Measurement
Command
Sequence
The steps for measuring temperature with the VT1529B and VT1586A
should, again, be familiar. If a controlled temperature isothermal block is
used, the command sequence is identical, except for the :POST keyword
being added to some commands. Otherwise, the isothermal block
temperature needs to measured, the major difference being that it is
necessary to measure the excitation voltage, thermistor output voltage, and
thermocouple voltage instead of just the thermistor and thermocouple voltage.
This is because the VT1529B with VT1586A excites the thermistor with the
excitation supply voltage that is provided instead of a calibrated current.
The thermistor measurement channel must be associated with its excitation
voltage measurement channel as well as associating each thermocouple to
the thermistor. The excitation voltage and thermistor measurement channels
must be part of the scan list. Figure 5-7 shows the sequence of
VXIplug&play driver calls to configure and scan thermocouple channels
using the new functionality.
Figure 5-7. Sequence for VT1529B Temperature Conversion
Periodic Calibration
Retrieve readings from
FIFO and/or CVT
Trigger event for each pass
through Scan List
Set up Trigger System to scan
temperature channels
Set up the analog input Scan List
Set up thermistor measurement
To convert readings to
Engineering Units of temperature
hpe1422_cmd(vi, "SENS:FUNC:TEMP:POST TC,
,(@
)");
<tc_type>
<ch_list>
hpe1422_cmd(vi, "SENS:REF:POST THER,5000,(@
),(@
)");
<exc_ch>
<thr_ch>
hpe1422_cmd(vi, "ROUTe:SEQuence:DEFine (@
,
),
<ch_list> <thr_ch>
hpe1422_cmd(vi, "TRIG:SOURce
");
<source>
Similarly with TRIG:COUNt, ARM:SOURce, TRIG:TIMer
Set up Sample Timer for best
channel-to-channel scan rate
Initiate Trigger System
hpe1422_cmd(vi, "SAMPle:TIMer 40e-6");
hpe1422_cmd(vi, "INITiate:IMMediate");
hpe1422_cmd(vi, "*TRG"); (if TRIG:SOUR HOLD set)
EXTernal trig, TTLTRGn signal, or TRIG:TIMer
hpe1422_readFifoPost_Q(vi, , ,
,
&rdgs_array);
<n_scans> <n_extra> <size>
Set Input Filter on VT1529B
hpe1422_cmd(vi, "INPut:FILTer:FREQuency
");
<freq>
Must include thermistor and excitation voltage channels.
hpe1422_cmdInt32_Q(vi, "*CAL?", &result);
hpe1422_cmdInt32_Q(vi, "CAL:REM? (@
)", &result);
<ch_list>
hpe1422_cmd(vi, "INPut:FILTer:STATe
");
<state>
hpe1422_cmd(vi, "TRIG:IMM");
Associate TC channels to
hpe1422_cmd(vi, "SENS:REF:CHAN:POST (@
),(@
)");
<thr_ch>
<ch_list>
thermistor
(@
)");
<exc_ch>