PT100 3 wire, how exactly does it work?
PT100 3 wire, how exactly does it work?
(OP)
Dear Users,
I have been trying to figure out the math behind the PT100 3-wire connection. All available material states that the lead resistance cancels itself out. But I am having trouble setting up the formulas that show this.
I have a system with a PT100 connected via 3-wires (5mtr). I use 3VDC as excitationvoltage and my bottomresistor is 200R. I see a significant change in measured temperature if I connect the PT100 device directly to my PCB without the wires.
So, if anyone could so kind as to help me understand the math involved, especially the leadcancelling, I would be most thankfull.
Thanking you in advance.
Henrik
I have been trying to figure out the math behind the PT100 3-wire connection. All available material states that the lead resistance cancels itself out. But I am having trouble setting up the formulas that show this.
I have a system with a PT100 connected via 3-wires (5mtr). I use 3VDC as excitationvoltage and my bottomresistor is 200R. I see a significant change in measured temperature if I connect the PT100 device directly to my PCB without the wires.
So, if anyone could so kind as to help me understand the math involved, especially the leadcancelling, I would be most thankfull.
Thanking you in advance.
Henrik





RE: PT100 3 wire, how exactly does it work?
If you want true cancellation, you need to use a 4-wire configuration.
TTFN
RE: PT100 3 wire, how exactly does it work?
Next you measure the the voltage between the non-excitation (white) lead and the red lead. This represents the RTD's temperature resistance AND the red lead voltage drop due to the excitation current.
You add the first white lead measurement voltage (which was negative) to this last measurement and it cancels any contribution to the RTD resistance measurement contributed to the red lead because of excitation current.
RE: PT100 3 wire, how exactly does it work?
The third wire senses the volt-drop of one of the current carrying wires, and the calculation bases its assumption that the other, unsensed volt-drop is equal to the first. Once the voltage across the RTD is known, Ohm's Law takes over.
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RE: PT100 3 wire, how exactly does it work?