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How a three wire RTD compensates for the resistance if it's lead wires.



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hey my name is Stuart brunt and today

I'm gonna explain how a 3-yr TD can

compensate for the natural resistance of

the wires that it's made of okay so

let's get started now if an RTD is a

resistance temperature detector and it's

important to know that it works by

changing its resistance based on the

temperature that's its sensing so it's

very important that we only use the

resistance change here we do not want

the resistance the natural resistance of

the wires that it's made of and all

wires have a natural resistance it's

inescapable and that resistance

increases with distance so we need to

compensate for this natural resistance

so that we can only use this resistance

and this is how we do it it's only three

three steps it's really two steps we're

gonna measure the resistance between

number one and number two what I mean by

that is we're gonna measure the

resistance of this wire and this wire

okay we're gonna subtract the resistance

between two and three we're going to

subtract the resistance that this wire

and this wire create and it's important

to know that all three of these wires

are made of the same thing otherwise

this compensation is going to be

inaccurate so really this is what we're

looking at the resistance of one of wire

one and two and the resistance of the

bulb subtracted from the resistance of

two and three so what happens here is

you're gonna have this and this we're

gonna cancel this and this are gonna

cancel and now you're just left with the

resistance of the bulb and now we've

compensated for all the excess

resistance and we have an accurate

temperature indication all right well I

hope this was helpful if you have any

questions or comments please leave them

in the links below alright catch you

later