3-wire resistance measurement

a defined current is initially applied between the contact points RL+ und RL- and the resistance between them is determined on the basis of the voltage drop.
The same procedure is subsequently carried out at the contact points R+ und RL-.
The difference between the two measurements is the line resistance of one of the cores of the sensor cable. By knowing the line resistance the resulting measuring error can be compensated.
The cores of the sensor cable must have the same resistance in order for the method to work.

The box uses the following calculation rule

With the values:

	Index in the CoE directory with n: channel number with 0 ≤ n ≤ 3 (channel 1 - 4)
X₁: raw value of the 1^st measurement	0x80nE:01
X₂: raw value of the 2^nd measurement	0x80nE:03
	Pt100	Pt1000
Gv₁: Vendor gain, 1^st measurement	0x80nF:04	0x80nF:0A
Ov₁: Vendor offset, 1^st measurement	0x80nF:03	0x80nF:09
Gv₂: Vendor gain, 2^nd measurement	0x80nF:02	0x80nF:08
Ov₂: Vendor offset, 2^nd measurement	0x80nF:01	0x80nF:07
Y_R1: Output value in 1/256 Ω	0x80nE:02
Y_R2: Output value in 1/256 Ω	0x80nE:04
Y_R: Output value in 1/256 Ω

	Overflow Y_R1and Y_R2 after 16 bits These values are only for fault finding. The registers overflow after 16 bits, i.e. at 65536.