×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Difference between 2-wire and 4-wire rtd

Difference between 2-wire and 4-wire rtd

Difference between 2-wire and 4-wire rtd

(OP)
Can someone tell me the difference between 2-wire ans 4-wire RTD. What are the relative merits/demerits

RE: Difference between 2-wire and 4-wire rtd

Three and four wire RTDs permit compensation for the cable resistance in long distance measurements.

John

RE: Difference between 2-wire and 4-wire rtd

Correct.  4-wire rtd enables a 4-wire resistance measurement. One pair of leads is the current/source leads, the other pair of leads are the voltage/sensing leads.

Power (voltage or current) is applied at the current/source leads which run to the 2 terminals of the rtd.  The only quantity measured in this set of leads is the current.  There is a voltage drop in these leads due to high (relatively) current flow but it is irrelevant since we do not measure voltage on these leads, only current.

The voltage/sensing leads run independently and connect to the same two terminals at the rtd to sense to voltage there. At the instrument there is a high-impedance volt measuring device which ensures virtally no current flow. Therefore no lead voltage drop and an accurate current measurement.

Resistance is calcualted as voltage (from volt/sensing leads) divided by current (from current/source leads).

This same principle is used in many instruments other than rtd.

3-wire rtd runs doulbe lead to one terminal of the rtd and signle lead to the other terminal.  Lead voltage drop is estimated based on comparing the two leads in the double pair.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources