VXI VT1422A, User Manual

Page: 153 / 529

Programming the VT1422A for Data Acquisition and Control 151 Chapter 4
Custom Thermocouple
EU Conversions
The VT1422A can measure temperature using custom characterized
thermocouple wire of types E, J, K, N, R, S, and T. The custom EU table
generated for the individual batch of thermocouple wire is loaded to the
appropriate channels using the DIAG:CUST:PIEC command. Since
thermocouple EU conversion requires a "reference junction compensation"
of the raw thermocouple voltage, the custom EU table is linked to the
channel(s) using the command [SENSe:]FUNCtion:CUSTom:TCouple
<
type >[,< range >],(@< ch_list >).
The < type > parameter specifies the type of thermocouple wire so that the
correct built-in table will be used for reference junction compensation.
Reference junction compensation is based on the reference junction
temperature at the time the custom channel is measured. For more
information, see “Thermocouple Reference Temperature Compensation” on
page 114.
Custom Reference
Temperature EU
Conversions
The VT1422A can measure reference junction temperatures using custom
characterized RTDs and thermistors. The custom EU table generated for the
individually characterized transducer is loaded to the appropriate channel(s)
using the DIAG:CUST:PIEC command. Since the EU conversion from this
custom EU table is to be considered the "reference junction temperature",
the channel is linked to this EU table using the command
[SENSe:]FUNCtion:CUSTom:REFerence [<
range >,](@< ch_list >).
This command uses the custom EU conversion to generate the reference
junction temperature as explained in the section “Thermocouple Reference
Temperature Compensation” on page 114.
Creating Conversion
Tables
Contact a VXI Technology System Engineer for more information on
creating Custom Engineering Unit Conversion.
Loading Custom EU
Tables
There is a specific location in the VT1422A’s memory for each channel’s
EU Conversion table. When standard EU conversions are specified, the
VT1422A loads these locations with EU conversion tables copied from its
non-volatile flash memory. For Custom EU conversions, these table values
must be loaded using either of two SCPI commands.
Loading Tables for Linear Conversions
The DIAGnostic:CUSTom:MXB < slope >,< offset >, (@< ch_list >) command
sends the <slope> and <offset> parameters that allow the driver to calculate
and download a custom linear Engineering Unit Conversion table to the
VT1422A for each channel specified.
•
< slope > specifies the linear function’s "slope":
•
< offset > specifies the conversion offset at zero input volts.
This parameter is also commonly known as the "Y-intercept."
•
< ch_list > specifies which channels will have this custom EU table loaded.
f
outp 1
f
outp 0
–
( )
V
in 1
V
in 0
–
( ) ⁄