Signal Conditioning Arrangements

Feature	Plug-in boards	Direct-connect modules	Two-wire transmitters	Distributed I/O
Location	Inside PC slot	External module wired to the DAQ	Mounted near sensor	Remote nodes on a network
Output	Raw digital via PC bus	Conditioned analog or digital	4-20 mA current loop	Digital over RS-485 or Ethernet
Distance	Short	Short to medium	Long (hundreds of metres)	Very long
Noise immunity	Low (inside PC)	Medium	High (current signal)	High
Channels	Limited by slots	Moderate	One per transmitter	Many nodes
Cost	Low	Medium	Medium	High
Use	Lab setups	Industrial measurement	Process control	Large plants

Key points

• Plug-in boards: ADC plus conditioning on a card in the computer; fast, but noisy PC environment.
• Direct-connect modules: sensor connects to a conditioning module (e.g. SCXI-type) which then connects to the DAQ.
• Two-wire transmitters: the same two wires carry power and the 4-20 mA signal; live zero (4 mA) allows wire-break detection.
• Distributed I/O: remote units digitize locally and send data over a network, avoiding long analog runs.

Exam tip

A comparison table like the above gets full marks; mention 4-20 mA.