Texas Instruments XTR108, User Manual

Page: 59 / 65

I
OUT
=
V
OUT
*50
R
VI
I
LIN_A
=
I
REF_B
*A
PGA
*50*(RTD
MAX
-RTD
MIN
)
R
VI
I
LIN_B
= I
OUT_MAX_MEAS_2
±
I
OUT_MIN
G
LIN_MEAS_A
=
I
LIN_B
±
I
LIN_A
(RTD
MAX
-R
Z_A
)*I
LIN_B
G
LIN_FINAL
= G
LIN_A
*
G
LIN_A
G
LIN_MEAS_A
N
14_A
= round(16*G
LIN_FINAL
*R
LIN
)
www.ti.com
Appendix
59 SBOU123A – March 2012 – Revised September 2016
Submit Documentation Feedback
Copyright © 2012–2016, Texas Instruments Incorporated
XTR108EVM-USB Evaluation Board and Software Tutorial
8.2.3 Second Corrections
Measure the output current at the maximum temperature (I
OUT_MAX_MEAS_2
).
8.2.3.1 Linearization Register
Calculate the final corrections for the linearization register. This step completes the calibration procedure.
8.3 XTR108 Calibration Equations (Voltage-Output Mode)
The calibration procedure for voltage-output mode is exactly the same as for current-output mode. The
only difference is that output voltage must be converted to output current in order to satisfy the same sets
of equations. Use the following equation to convert output voltage to output current.
8.4 Mnemonic Commands
The USB-DAQ platform uses a set of mnemonic commands to perform SPI communications to the
XTR108EVM-USB. These commands are given in
Table 31 .
Table 31. Mnemonic Commands
Command Description
SPI Always the first mnemonic in an SPI command.
CH1
CH2
Always the second mnemonic in an SPI command.
This mnemonic identifies which SPI channel is used. The USB-DAQ platform contains
two SPI channels to allow for the connection of two different SPI devices.
BREH
BREL
AFEH
AFEL
Always the third mnemonic in an SPI command.
This mnemonic identifies different modes of SPI data capture. For example, BREL
means that the data are captured before the clock rising edge and the clock is active
low. Further details are included in
Table 32 .
L Drive chip select (CS) line low
H Drive chip select (CS) line high
R Read an 8-bit word
Example: 01h, 3Ah, and 9Ch Write an 8-bit word (any hexadecimal two-character byte)