LTC2984_15 Datasheet, PDF (42/78 Pages) Linear Technology – Multi-Sensor High Accuracy Digital Temperature Measurement System with EEPROM

LTC2984
APPLICATIONS INFORMATION
Example: Standard 4-Wire RTD (No Rotation or R_SENSE
Sharing)
Standard 4-wire RTD channel assignments follow the
general convention shown in Figure 16. Terminal 1 is
tied to ground, terminals 2 and 3 (Kelvin sensed signal)
tie to CH_RTD and CH_RTD-1, and the 4th terminal ties to the
sense resistor. Channel assignment data (see Table 29)
is mapped to memory locations corresponding to CH_RTD.
Sense resistor channel assignments follow the general
convention shown in Figure 17. The sense resistor is tied
between CH_RSENSE and CH_SENSE-1, where CH_RSENSE is
tied to the 4th terminal of the RTD. Channel assignment
data (see Table 37) is mapped into a memory location
corresponding to CH_RSENSE.
Figure 18 shows a typical temperature measurement
system using a 4-wire RTD. In this example, a 4-wire
RTD’s terminals tie to GND, CH₁₃, CH₁₂, and CH₁₁. The
sense resistor ties to CH₁₁ and CH₁₀. The sense resis-
tor and RTD share a common connection at CH₁₁. The
RTD sensor type and configuration data are assigned to
CH₁₃. 32 bits of binary configuration data are mapped
directly into memory locations 0x230 to 0x233 (see
Table 44). The sense resistor is assigned to CH₁₁. The
user-programmable value of this resistor is 5000.2Ω.
32 bits of binary configuration data are mapped directly
into memory locations 0x228 to 0x22B (see Table 46).
A conversion is initiated on CH₁₃ by writing 10001101
into the data byte at memory location 0x000. Once the
conversion is complete, the INTERRUPT pin goes HIGH
and memory location 0x000 becomes 01001101. The
resulting temperature in °C can be read from memory
locations 0x040 to 0x043 (corresponding to CH₁₃).
CH_RSENSE 4TH TERMINAL TIES TO SENSE RESISTOR (CH_RSENSE)
EXCITATION
CURRENT
FLOW
4 _{3 CHRTD-1}
2
1
CH_RTD
CHANNEL
ASSIGNMENT
= CH_RTD (2 ≤ RTD ≤ 20)
2984 F16
Figure 16. 4-Wire RTD Channel Assignment Convention
EXCITATION
CURRENT
FLOW
R_SENSE
CH_RSENSE-1
CH_RSENSE
CHANNEL
ASSIGNMENT
= CH_RSENSE (2 ≤ RSENSE ≤ 20)
2984 F17
Figure 17. Sense Resistor Channel Assignment Convention for
4-Wire RTDs
2984f
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