Motor RTD

[hanksmith]

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

 

[electricpete]

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


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[electricpete]

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

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[electricpete]

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

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[hanksmith]

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)

 

[roydm]

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

 

[danw2]

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.

 

[itsmoked]

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

 

[hanksmith]

danw2,

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

Thanks
Hank