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Module 4: DAQ Systems

20267m

Differentiate between RS-232, RS-485, Ethernet and USB interfaces used for data loggers.

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Data Logger Interfaces

Feature RS-232 RS-485 Ethernet USB
Signalling Single-ended, +/-3 to 15 V Differential Differential twisted pair Differential D+/D-
Devices 1 to 1 (point to point) Up to 32 or more nodes (multi-drop) Many via switch 1 host to many via hub
Max distance About 15 m About 1200 m 100 m per segment (copper) About 5 m per cable
Speed Up to 115.2 kbps (typ.) Up to 10 Mbps at short range 10/100/1000 Mbps 12 Mbps to several Gbps
Noise immunity Low High High Medium
Duplex Full Half (2 wire) or full (4 wire) Full Half or full
Power supply No No Optional (PoE) Yes (5 V bus)
Cost Low Low Medium Low
Typical use Old instruments, configuration Industrial networks, Modbus RTU Networked and remote logging Direct PC connection, download
MermaidDiagram
Rendering diagram…

Selection guide

  • Long distance, many loggers, noisy plant: RS-485.
  • Remote monitoring over a network: Ethernet.
  • Quick local download: USB.
  • Simple one-to-one legacy link: RS-232.

Exam tip

Write the table and a one-line use case for each interface.

Similar questions

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