VTI Instruments EX1401, User Manual

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EX1401 Basic Operation 45
streaming data, the data will be written directly to the device as soon as it becomes available in the
HDF5 file format.
In either case, retrieved data is fully calibrated and compensated by the EX1401 and output directly
in the requested units. No post-acquisition user manipulations are required. In order to provide the
maximum reading buffer capacity for future acquisitions, data is deleted from the FIFO memory
upon retrieval.
Applications may retrieve data from this FIFO using either the Read FIFO or Streaming Data
interfaces. Please refer to Data Acquisition in Section 5 for further details. Once data is retrieved
from the FIFO, via any method, it is no longer kept within the FIFO.
U
SER
-
DEFINED
C
ONVERSIONS
The EX1401 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. One unique set
of coefficients can be entered for each channel. 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, 1.0].
NOTE The entry of user-defined coefficients does not automatically enable their use. The enabling is done
by setting the Thermocouple Type to “Custom”.
LCD D
ISPLAY
The display on the rear side of EX1401 is a 20 x 2 backlit LCD. It can display several screens that
can be cycled through using the Menu button. Some screens allow you to initiate an action. This is
done by holding the menu button in for several seconds. A countdown of remaining seconds is
shown while the button is pressed. The action is activated on release of the menu button; releasing
before the countdown completes will cancel the action. Screens with actions are LAN Reset, Self-
Test, USB Eject, and USB Data Logging.
Hostname
Hostname
EX1401-681514
_______