ABB PSTX720 - Page 48

48 Connection | Installation and commissioning manual | 1SFC132081M0201
2-wire measurement for PTC
When you use 2-wire temperature sensors, the sensor
resistance and the wire resistance are added. Correct
for the resulting systematic errors when you change the
tripping device. Use
Table 1 Temperature errors in C°/K
to determine the temperature errors caused by the line
length. See Figure 5.24.
Tightening torques and cable dimensions.
0,2 .. 2,5 mm
2
2x0,2 .. 1,5 mm
2
0,2 .. 2,5 mm
2
2x0,2 .. 1,5 mm
2
AWG 12 ... 24
0,5 Nm
4,3 lb.in
3,5 x 0,6 mm
(0.138 x 0.024 in)
M3
23 24 25 26 27
T1 T2 T3
28 29 30
+(B) -(A) +24V + GND
Analog outTemp InCom 3
1
SFC132081M0201
Error caused by the line
The error caused by the line resistance is to
approximately 2.5 Kelvin/Ohm. If you don’t know the
resistance of the line and you cannot measure it, you can
make an estimation of the error caused by the line with
this table.
Temperature errors in °C / K
The table below shows temperature errors, at an ambient
temperature of 20° C, for different line lengths and
conductor cross sections for PT100 sensors.
Table 1 Temperature errors in C°/K
Line length in m Wire size mm
2
0.50 0.75 1 1.5
10 1.8 1.2 0.9 0.6
25 4.5 3.0 2.3 1.5
50 9.0 6.0 4.5 3.0
75 13.6 9.0 6.8 4.5
100
18.1 12.1 9.0 6.0
200
39.3 24.2 18.1 12.1
500
91.6 60.8 45.5 30.2
Figure 5.24
PTC - 2 wire
1SFC132081M0201
PTC - 2 wire
23 24 25 26 27
T1 T2 T3
28 29 30
+(B) -(A) +24V + GND
Analog outTemp InCom 3
5