Texas Instruments XTR108, Руководство пользователя

Страница: 53 / 65

R
CM
5.23k
:
R
Z2
R
Z3
R
Z4
R
Z5
R
Z1
187 :
RTD
PT1000
+
PGA
XTR108
T=850°C
3.905k
:
50 P A 50 P A
I
1
I
2
V
CM =
0.52V
0.718V
0.532V
1
0
0
P
A
5
0
P
A
5
0
P
A
Input differential voltage is
approximately 186mV at T
MAX
MUX
R
CM
523 :
R
Z2
R
Z3
R
Z4
R
Z5
R
Z1
18.7
:
RTD
PT100
+
PGA
XTR108
T=850°C
390.48
:
500
P
A 500
P
A
I
1
I
2
V
CM =
0.52V
0.718V
0.532V
1
0
0
0
P
A
5
0
0
P
A
5
0
0
P
A
Input differential voltage is
approximately 186mV at T
MAX
MUX
www.ti.com
Appendix
53 SBOU123A – March 2012 – Revised September 2016
Submit Documentation Feedback
Copyright © 2012–2016, Texas Instruments Incorporated
XTR108EVM-USB Evaluation Board and Software Tutorial
Figure 37 shows the same multiplexer configuration with the RTD at maximum temperature, where T
MAX
=
+850°C. At this point, the differential input voltage to the PGA is equal to 186 mV, the maximum value for
this configuration.
Figure 37. XTR108 Input MUX Example (T
MAX
= +850°C, PT100 RTD)
Figure 38 shows how the current sources can be programmed to accommodate different types of RTDs.
The previous example used a 100- Ω RTD, or PT100. In this example the RTD type has been changed to
1000
Ω
, or PT1000. The current sources I
1
and I
2
are scaled from 500 µA to 50 µA to accommodate this
new resistance. R
Z1
and R
CM
are also scaled appropriately. Note that I
1
and I
2
are matched current sources
that are programmed by one set of DACs (an 8-bit coarse DAC and 8-bit fine DAC). These current
sources are programmed during the calibration procedure.
Figure 38. XTR108 Input MUX Example (T
MAX
= +850°C, PT1000 RTD)