WAT12 accepts a wide range of input power 12 ... 28 V DC. When the 5 mA loop current is selected, the total current consumption is less than 40 mA including the sensors and the loop current. The low current consumption enables to remotely supply the operating power from a distance of several kilometers, even through private or leased telephone lines.
The maximum power line resistance depends on the supply voltage and the loop current selection. For an example with an 24 V DC power supply, see Figure 1.
| Loop current, mA | Power line resistance, Ω |
|---|---|
| 5 | 360 |
| 10 | 310 |
| 20 | 250 |
For other powering options, see Figure 2, Figure 3, and Figure 4
The power line is protected against the wrong polarity. Transient protection is accomplished with VDRs, series inductors and resistors, and transient zener diodes on both the power line and each I/O line.