Linear Technology LTC2983 - Page 39

LTC2983
39
2983fc
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Table 43. Channel Assignment Data for Rotating 4-Wire RTD (PT-100, R
SENSE
on CH
6
, Rotating 4-Wire, 100µA Excitation Current,
α = 0.003911 Curve)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) RTD TYPE PT-100 5 01100 0 1 1 0 0
(2) Sense
Resistor Channel
Pointer
CH
6
5 00110 0 0 1 1 0
(3) Sensor
Configuration
4-Wire with
Rotation
4 1010 1 0 1 0
(4) Excitation
Current
100µA 4 0101 0 1 0 1
(5) Curve American,
α=0.003911
2 01 0 1
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 44. Channel Assignment Data for Sense Resistor (Value = 10.0102kΩ)
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
10.0102kΩ 27 000100111000110100011001100 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 1 1 0 0 1 1 0 0
APPLICATIONS INFORMATION
Figure 18 shows a typical temperature measurement
system using a rotating 4-wire RTD. In this example
a 4-wire RTD’s terminals tie to CH
17
, CH
16
, CH
15
,
and CH
6
. The sense resistor is tied to CH
6
and CH
5
.
The sense resistor and RTD connect together at CH
6
.
The RTD sensor type and configuration data are as-
signed to CH
16
. 32 bits of binary configuration data are
mapped directly into memory locations 0x23C to 0x23F
(see Table 43). The sense resistor is assigned to CH
6
.
The user programmable value of this resistor is 10.0102kΩ.
32 bits of binary configuration data are mapped directly
into memory locations 0x214 to 0x217 (see Table 44).
A conversion is initiated on CH
16
by writing 10010000 into
memory location 0x000. Once the conversion is complete,
the INTERRUPT pin goes HIGH and memory location
0x000 becomes 01010000. The resulting temperature in
°C can be read from memory locations 0x04C to 0x04F
(corresponding to CH
16
).
Figure 18. Rotating 4-Wire RTD Example
R
SENSE
10.0102k
0.01µF
2983 F18
0.01µF
SENSE RESISTOR ASSIGNED TO CH
6
(CH
SENSE=6
)
RTD ASSIGNED TO CH
16
(CH
RTD=16
)
CH
6
CH
5
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x214 TO 0x217
CHANNEL ASSIGNMENT
MEMORY LOCATIONS 0x23C TO 0x23F
RESULT MEMORY LOCATIONS 0x04C TO 0x04F
0.01µF
CH
15
CH
16
CH
17
PT-100
0.01µF
0.01µF
3
4
2
1