×
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

Motor RTD

Motor RTD

Motor RTD

(OP)
Was in charge of updateing some drawings for a client and the wiring of the RTDs for the motor is different from one drawing to the next,

These RTD are being fed into a Multilin and was wondering what would happen if the RTD were wired to the multilin incorrecty, the motor has been working for a long time.

Thanks
Hank

RE: Motor RTD

Well, it depends on the miswiring.  If you removed lead compensation, the temperautre would read lower than actual.
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor RTD

... i.e. that would be shorting together the two common leads of 3-wire rtd.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor RTD

I'm sorry.  That particular error would cause higher indicated temperature than actual

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: Motor RTD

(OP)
ok, with a 3 wire RTD, there are 2 wires of one side of the RTD and one off the other side, if you mix one of the two wires with the one wire would that do anything? (did that make any sense)

When I look at this situation it seems that there would be a drastic change, (not sure whether higher or lower though)
 

RE: Motor RTD

Hanksmith,  you need to post a sketch of the 2 different wiring methods.
2 of the leads are identical and interchangeable.
If the 3rd lead is miss-wired the temperature reading will be so far out (low  i believe) it should have triggered alarm bells
Were 2 terminals jumpered at the Multilin?
Type of RTD 10 Ohm Cu, !00 Ohm Pt or something else?
Roy

RE: Motor RTD

Yes, there is a drastic change when mis-wired:

Suppose it's a 100 ohm DIN RTD with US color code
red, white1, white2

The two whites are connected to the same point:

red --resistor------ white1
              '----- white2

If the wires connected to your input are red and white1 the input sees the RTD resistance.

If the wires connected to your input are red and white2 the input sees the RTD resistance.

If the wires connected to your input are white1 and white2 the input sees a virtual short circuit; only the resistance of the copper running out to the motor and back again.  Such a very low resistance would be interpreted as a very, very low temperature, if not an error or failed input.

As others mentioned, if the second white wire is not used for lead wire compensation, then the temperature reading will be high, since the resistance of the lead wire is added to the RTD resistance, a higher resitance represents a higher temperature.

RE: Motor RTD

Not noted yet is that if the Multilin is expecting a two wire RTD then you shouldn't actually be using both of the whites just one.   But using both the whites in lue of just one would probably represent only a degree or two difference at most.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Motor RTD

(OP)
danw2,

That pretty much nailed my question and confirmed what I was thinking.

Thanks
Hank

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