LTC2414 LINER [Linear Technology], LTC2414 Datasheet - Page 41

• Manufacturer Part Number: LTC2414
• Description: 8-/16-Channel 24-Bit No Latency TM ADCs
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
MULTIPLE CHANNEL USAGE
The LTC2414/LTC2418 have up to sixteen input channels
and this feature provides a very flexible and efficient
solution in applications where more than one variable
need to be measured.
Measurements of a Ladder of Sensors
In industrial process, it is likely that a large group of real
world phenomena need to be monitored where the speed
is not critical. One example is the cracking towers in
petroleum refineries where a group of temperature mea-
surements need to be taken and related. This is done by
passing an excitation current through a ladder of RTDs.
The configuration using a single LTC2418 to monitor up to
eight RTDs in differential mode is shown in Figure 48. A
high accuracy R1 is used to set the excitation current and
the reference voltage. A larger value of 25k is selected to
U
TWO ELEMENTS
350Ω BRIDGE
Figure 47. Use Resistor Arrays to Provide Precise Matching in Excitation Amplifier
VARYING
U
2N3904
2N3906
Q2, Q3
22Ω
33Ω
10V
×2
Q1
×2
–15V
W
15V
–5V
1
5
20Ω
RN1
RN1
10k
10k
20Ω
2
6
U
1
7
C1
0.1µF
C2
0.1µF
LT1112
LT1112
–15V
8
4
15V
1/2
1/2
reduce the self-heating effects. R1 can also be broken into
two resistors, one 25k to set the excitation current and the
other a high accuracy 1k resistor to set the reference
voltage, assuming 100Ω platinum RTDs. This results in a
reduced reference voltage and a reduced common mode
difference between the reference and the input signal,
which improves the conversion linearity and reduces total
error.
Each input should be taken close to the related RTD to
minimize the error caused by parasitic wire resistance.
The interference on a signal transmission line from RTD to
the LTC2418 is rejected due to the excellent common
mode rejection and the digital LPF included in the LTC2418.
It should be noted that the input source resistance of CHO
can have a maximum value of 800Ω • 8 = 6.4k, so the
parasitic capacitance and resistance of the connection
wires need to be minimized in order not to degrade the
converter performance.
+
–
–
+
3
4
3
2
6
5
RN1
10k
8
7
RN1
10k
RN1 IS CADDOCK T914 10K-010-02
+
5V
11
12
21
22
C3
47µF
REF
REF
CH0
CH1
LT1236-5
LTC2414/
LTC2418
LTC2414/LTC2418
+
–
GND
V
CC
9
15
2410 F53
C1
0.1µF
5V
41
241418fa