Panametrics DewPro MMY30, Руководство пользователя, Страница: 22 / 43

Chapter 3. Wiring Instructions
14 DewPro
®
MMY30 User’s Manual
3.2.2 Designing the Loop
When selecting a power supply, please note that the voltage at the +/- terminal of the DewPro MMY30 should not fall
below 12 VDC. The maximum loop resistance is an important parameter for selection of the supply voltage. Each
device connected to the loop causes a voltage drop. For instance, Ohm’s law indicates that using a loop-powered
display with an input impedance of 50 Ohms will cause a voltage drop of 1 VDC at 20 mA. Likewise, connecting the
loop to a PLC (Programmable Logic Controller) will cause a voltage drop across the input.
When designing your loop, add up all voltage losses across the devices connected to the loop and add 12 V. Then,
add a 20% safety factor and the sum will be the minimum supply voltage required from the power supply.
3.3 Mounting in Normal Environments
A standard two-wire, stranded cable (as shown in Figure 11 below) can be used to interconnect the DewPro MMY30
with the power source.
Figure 10: DewPro MMY30 Interconnections
External Earth Ground
Two-Wire Cable
Capped