Linear Technology LTC2983 - Page 42

LTC2983
42
2983fc
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Table 48. Channel Assignment Data for 4-Wire RTD with Kelvin Connected R
SENSE
(PT-10, R
SENSE
on CH
6
, 4-Wire, Kelvin R
SENSE
with
Rotated 1mA Excitation Current, α = 0.003916 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) RTD TYPE PT-10 5 01010 0 1 0 1 0
(2) Sense Resistor
Channel Pointer
CH
6
5 00110 0 0 1 1 0
(3) Sensor
Configuration
4-Wire Kelvin R
SENSE
and Rotation
4 1110 1 1 1 0
(4) Excitation Current 1mA 4 1000 1 0 0 0
(5) Curve Japanese, α=0.003916 2 10 1 0
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Figure 21 shows a typical temperature measurement system
using a 4-wire RTD with a Kelvin connected R
SENSE
. In this
example, the 4-wire RTD’s terminals tie to CH
17
, CH
16
, CH
15
,
and CH
6
. The sense resistor ties to CH
6
, CH
5
, and CH
4
and
excitation current is applied to CH
4
and CH
17
. The sense
resistor’s nominal value is 1kΩ in order to accommodate a
1mA excitation current. The sense resistor and RTD connect
together at CH
6
. This topology supports both rotated, shared
and standard 4-wire RTD topologies. If rotated or shared
configuration are not used then terminal 1 of the RTD is tied to
ground instead of CH
17
, freeing up one input channel. Channel
assignment data is shown in Tables 48 and 49.
A conversion is initiated on CH
16
by writing 10010000
into memory location 0x000. Once the conver-
sion is complete, the INTERRUPT pin goes HIGH
and memory location 0x000 becomes 01010000
(see Table 6). The resulting temperature in °C can be read from
memory locations 0x04C to 0x04F (corresponding to CH
16
).
APPLICATIONS INFORMATION
Figure 21. Sense Resistor with Kelvin Connections Example
2983 F21
SENSE RESISTOR ASSIGNED TO CH
6
(CH
SENSE=6
)
CH
4
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x214 TO 0x217
0.01µF
CH
5
CH
6
CH
15
CH
16
CH
17
RTD ASSIGNED TO CH
16
(CH
RTD=16
)
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
RESULTS MEMORY LOCATIONS 0x04C TO 0x04F
R
SENSE
1k
0.01µF
0.01µF
3
4
2
1
0.01µF
4-WIRE PT-10
0.01µF
0.01µF
3
4
2
1
Table 49. Channel Assignment Data for Sense Resistor (Value = 1000Ω)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x214
MEMORY
ADDRESS 0x215
MEMORY
ADDRESS 0x216
MEMORY
ADDRESS 0x217
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
1000Ω 27 000000011111010000000000000 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0