Panametrics DewPro MMR31, Руководство по установке и эксплуатации, Страница: 16 / 45

Chapter 2. Installation
8 DewPro<Superscript>® MMR31 Installation & Operation Manual
2.2 Wiring Configurations with One Current Loop
CAUTION!
The MMR31 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 circuit boards.
2.2.1 General Guidelines
The maximum loop resistance is an important parameter for selection of the supply voltage, because each device
connected to the loop causes a voltage drop. For instance, using a loop-powered display with an input impedance
of

50 ohms will cause a voltage drop of 1 VDC at 20 mA, per Ohm's law (V = R x I = 50 x 0.020 = 1). Similarly, connecting
the loop to a Programmable Logic Controller (PLC) will cause a voltage drop across its input.
When designing your loop, add up all voltage drops across the devices connected to the loop and then add 12 V. This
sum is the minimum supply voltage required for the circuit. To ensure reliable operation, it is recommended that a
20% safety factor be added to the calculated voltage requirement.
IMPORTANT: The voltage across the + and - terminals of the MMR31 should not fall below 12 VDC.
If an external display is used, configure it to the proper range: 0-100% RH, 5 to 185°F (–15 to +85°C) dew point,

1 to 350 g/m
3
absolute humidity, 1 to 830 g/kg mixing ratio, or custom range corresponding to 4–20 mA. Figure 5
below illustrates some common system configuration options.
Customer’s Power Supply
24 VDC (12-28 VDC)
Power Supply
(available from Panametrics)
Power Supply with Display and Optional Relay
(available from Panametrics)
115/230 VAC
115/230 VAC
Figure 5: System Configuration Options