Figure 69: Current Loop Output Ranges - GE P642 Technical Manual

Chapter 7 - Transformer Condition Monitoring
Current Output
1 mA
0 mA
Minimum
Current Output
20 mA
0 mA
Minimum
E03206

Figure 69: Current Loop Output ranges

Note:
If the Maximum is set less than the Minimum, the slopes of the graphs will be negative.
The transducers inside the device are of the current output type. This means that the correct value of output is
always maintained over the load range specified. The range of load resistance varies a great deal, depending on
the design and the value of output current. Transducers with a full-scale output of 10 mA will normally feed any
load up to a value of 1000 ohms (compliance voltage 10V). This equates to an approximate cable length of 15 km.
We recommend using a screened cable, earthed at one end. This helps reduce interference on the output current
signal. The table below shows typical cable impedances per kilometer for common cables. The compliance voltage
dictates the maximum load that a transducer output can feed. Therefore, the 20 mA output will be restricted to a
maximum load of 500 ohms.
Cable
CSA (mm2)
R (ohms/km)
You can connect the receiving equipment at any point in the output loop and install additional equipment later.
You do not need to adjust the transducer output, providing the compliance voltage is not exceeded.
Where you use the output current range for control purposes, you may wish to fit appropriately rated diodes, or
Zener diodes, across the terminals of each of the units in the series loop. This will guard against the possibility of
their internal circuitry becoming open circuit. In this way, a faulty unit in the loop does not cause all the indications
162
Relay
Measurement
Maximum
0 - 1 mA
Relay
Measurement
Maximum
0 - 20 mA
1/0.6 mm
0.28
65.52
Current Output
10 mA
0 mA
Minimum
Current Output
20 mA
4 mA
0 mA
Minimum
4 - 20 mA
1/0.85 mm
0.57
32.65
Relay
Measurement
Maximum
0 - 10 mA
Minimum
Relay
Measurement
Maximum
1/1.38 mm
1.50
12.38
P64x-TM-EN-1.3
P64x