LTC2983
34
2983fc
For more information www.linear.com/LTC2983
APPLICATIONS INFORMATION
Example: 3-Wire RTD
3-wire RTD channel assignments follow the general con-
vention shown in Figure 10. Terminals 1 and 2 tie to the
input/excitation current sources and terminal 3 connects
to the sense resistor. Channel assignment data is mapped
to memory locations corresponding to CH
RTD
.
Table 37. Channel Assignment Data for 2-Wire RTD #2 (NI-120, R
SENSE
on CH
16
, 2-Wire, Shared R
SENSE
, 100µA Excitation Current)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x24C
MEMORY
ADDRESS 0x24D
MEMORY
ADDRESS 0x24E
MEMORY
ADDRESS 0x24F
(1) RTD TYPE NI-120 5 10001 1 0 0 0 1
(2) Sense Resistor
Channel Pointer
CH
16
5 10000 1 0 0 0 0
(3) Sensor
Configuration
2-Wire with
Shared R
SENSE
4 0001 0 0 0 1
(4) Excitation
Current
100µA 4 0101 0 1 0 1
(5) Curve European
α = 0.00385
2 00 0 0
(6) Custom RTD
Data Pointer
Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0
Table 38. Channel Assignment Data for Sense Resistor (Value = 5001.5Ω)
CONFIGURATION
FIELD
DESCRIPTION # BITS BINARY DATA MEMORY
ADDRESS 0x23C
MEMORY
ADDRESS 0x23D
MEMORY
ADDRESS 0x23E
MEMORY
ADDRESS 0x23F
(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1
(2) Sense
Resistor Value
5001.5Ω 27 000010011100010011000000000 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0
Sense resistor channel assignments follow the general
convention shown in Figure 11. The sense resistor is tied
between CH
RSENSE
and CH
RSENSE-1
, where CH
RSENSE
is
tied to the 3rd terminal of the RTD and CH
RSENSE-1
is tied
to ground (or left floating for R
SENSE
sharing). Channel
assignment data (see Table 33) is mapped into the memory
location corresponding to CH
RSENSE
.
Figure 10. 3-Wire RTD Channel Assignment Convention
Figure 11. 3-Wire Sense Resistor Channel Assignment
Convention for 3-Wire RTDs
2983 F10
3RD TERMINAL TIES TO SENSE RESISTOR
2
3
1
CH
RTD-1
CH
RSENSE
CH
RTD
EXCITATION
CURRENT
FLOW
= CH
RTD
(2≤ RTD ≤ 20)
CHANNEL
ASSIGNMENT
2983 F11
CH
RSENSE-1
CH
RSENSE
R
SENSE
2x EXCITATION
CURRENT
FLOW
= CH
RSENSE
(2≤ RSENSE ≤ 20)
(OPTIONAL GND, REMOVE FOR R
SENSE
SHARING)
CHANNEL
ASSIGNMENT
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