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4 wire rtd with one wire not connected
- Thread starter Yarno
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Some circuits use three wires.
The third wire is used to cancel out conductor resistance.
Some circuits use four wires for the same thing, cancelling loop conductor resistance.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
The third wire is used to cancel out conductor resistance.
Some circuits use four wires for the same thing, cancelling loop conductor resistance.
Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!
4-wire Kelvin connection is the gold standard for eliminating resistive parasitics from the measurement. 2-wire basically sucks for low-resistance measurements, since contact resistance is often on the order of 0.5 ohm. 3-wire is kind of a compromise, often because someone got lazy in running the 4th wire, or couldn't because of an existing layout.
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Read what I wrote in this thread:
thread240-165067
It explains how three wire RTDs are used. Three wire are THE most common version.
Keith Cress
kcress -
thread240-165067
It explains how three wire RTDs are used. Three wire are THE most common version.
Keith Cress
kcress -
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A 4-wire configuration is the most precise/accurate, particularly if the RTD or whatever resistor isn't soldered in place, i.e., a switching network or clips are used; the 4th wire allows the parasitic resistances on both sides of the resistor to be eliminated from the measurement
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I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
I suspect that if you re-draw your diagram you'll find that the unlabeled R's and R3 form a classic bridge circuit for a 3-wire RTD; and Rd1, Rd2 and Rd4 being the lead resistance.
Compare to the 3-wire RTD circuit from Wikipedia (of all places):
Compare to the 3-wire RTD circuit from Wikipedia (of all places):
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