VTI Instruments EX1000A, User Manual

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EX10xxA Triggering 69
U
SER
-
DEFINED
C
ONVERSIONS
The EX10xxA nominally accepts standard thermocouple types and performs its thermocouple
calculations using polynomial coefficients from the NIST ITS-90 Thermocouple Database. In some
applications, however, a user may want to override the embedded coefficients with a user-defined
coefficient set. One reason to do this is if the transfer function of the specific thermocouple being
used has been completely characterized to an accuracy level that exceeds standard thermocouple
limits of error. Another reason to do this is if a non-standard thermocouple is used. Up to two unique
sets of coefficients can be entered. Specifically, the use of custom thermocouple equations requires
the user to know or generate the coefficients for two conversion polynomials.
The forward conversion polynomial is used to convert a CJC temperature into a compensating cold
junction voltage and has the form of:
12
12
2
2
1
1 0
* * * t c t c t c c E
     
where E is in volts, t is in ºC, and c
0
- c
12
are the coefficients.
The inverse conversion polynomial is used to convert a compensated input voltage into temperature
and has the form of:
12
12
2
2
1
1 0
* * * E d E d E d d t
     
where E is in volts, t is in ºC, and d
0
- d
12
are the coefficients.
The default values for the coefficients are 0.0.
NOTE The entry of user-defined coefficients does not automatically enable their use. The enabling is done
by setting the EU conversion to User0 or User1.