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4.2.3 Lengthening a cable in 4-wire technology
As mentioned above the connection should be in 6 wire technology if the sensor comes with no hard-
mounted cable or the existing cable is to be lengthened.
Example: The sensor has been calibrated with an excitation of 10,000 V.
Pic. 2: Connection in 4-wire technology; drop of SG-Excitation voltage caused by cable lengthening (0,5 Ohm)
In the picture above the original cable has been lengthened and this additional cable results in a
resistance increasing of 0,5 ohms. Thus, the excitation voltage drops by 0,03 V (resp. 30 mV) which
results a measurement inaccuracy of 0,3 %.
Pic. 3: Sensor with 4 wire cable. Lengthened with 6 wire cable
In the picture above the cable has been lengthened with a 6-wire cable, so the voltage drop of 30 mV
is corrected by the amplifier by measuring the actual voltage at the end of the original cable.
SG-Amplifier
SG-Signal
SG-Excitation voltage
9,97 V
+Sense
+SG-Excitation
-Sense
-SG-Excitation
Transducer cable
SG-Excitation voltage
10,00 V
R
wire=0,5 Ohm
R
wire=0,5 Ohm
350 Ohm
Cable lengthening
SG-Amplifier
SG-Signal
SG-Exctiation voltage
10,00 V
+Sense
+SG-Excitation
-Sense
-SG-Excitation
Transducer cable
SG-Excitation voltage
10,03 V
350 Ohm
R
wire=0,5 Ohm
