3 and 4 wire RTD's uncompensated?

Anybody else think that the notes (highlighted in red) is a misprint in the Siemens S7-300 manual for the 7KB02 analog input module RTD wiring?



It should be
4 wire connection
3 wire connection
2 wire connection, no compensation for line resistnace

nicht wahr?

Or maybe they are trying to say you don't need compensation with 4 and 3 wire RTD's but you do/ should with 2 wire.

Sometimes reading is just not enough.

How about the're meanning is that you don't need compensation 'cause the darn thing is doing it on its own?

From Korean to Chinese then to English ... lost in translation!

My 2 cents...

Pierre said:

Sometimes reading is just not enough.

How about the're meanning is that you don't need compensation
'cause the darn thing is doing it on its own?
From Korean to Chinese then to English ... lost in translation!

My 2 cents...

Click to expand...

In my view they mean exactly what they say - there will be no compensation.

When you connect a 2-wire RTD, you cannot compensate for line resistance, and that is why they are seldom used.

A 3-wire RTD compensates for line resistance by measuring it on one leg only, then doubling it. A low-cost method, that generally works well for a single cable-run to the RTD.

A 4-wire RTD compensates by measuring both legs, and is the most accurate.

the compensation switch in the lower part is used to switch between the inner compensation, external compensation and none.
If using only 2 wires connect a resistor on the outer connections (not to ground) of about the resistance of the leads. If possible use 1 pair of wires in the cable. this way you can use 8 sensors with 10 wires.
for 3 and 4 wire use the internal compensation. it is autodetecting 3 way and 4 way.
the switch in none means a short on external compensation is same.
if you must use 2 wire do ice test and set to zero, write down how much you have to compensate.
it is precise within about 1 celsius, if better you must use more wires.

Thanks Paul for that description of the compensation switch.

Is that printed somewhere and I missed it or is it "oral tradition" passed down from generation to generation?