Panametrics DewPro MMR30, Installation & Operation Manual

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DewPro® MMR30 Installation & Operation Manual 11
Chapter 3. Wiring Instructions
Chapter 3. Wiring Instructions
3.1 Wiring, General Guidelines
CAUTION!
The DewPro system contains electronic components that are susceptible to damage by
static electricity. Proper handling procedures must be observed during the removal,
installation, or other handling of internal boards or devices.
Note: If the DewPro is equipped with an optional display/user interface, please refer to Chapter 4.
3.2 System Configuration
Figure 10 below shows various power supplies and displays for use with the DewPro.
Figure 10: Power Supplies and Displays for DewPro
3.2.1 Designing the Loop
If users provide their own power supply, the voltage at the +/- terminal of the DewPro should not fall below 12 VDC.
The maximum loop resistance is an important measure for selection of the supply voltage. Each device connected to
the loop causes a voltage drop. For instance, using a loop-powered display with an input impedance of 50 Ohm will
cause a voltage drop of 1 VDC at 20 mA using Ohm's law. Connecting the loop to a PLC 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. The sum
will be the minimum supply voltage required from the power supply. Calculate with a 20% safety factor.