Panametrics DewPro MMR31 User manual

panametrics.com
Moisture
A40251532 Rev.C
July 2020
DewPro® MMR31
Installation & Operation Manual

Moisture
panametrics.com
Copyright 2020. Baker Hughes company.
This material contains one or more registered trademarks of Baker Hughes Company and its subsidiaries
in one or more countries. All third-party product and company names are trademarks of their respective
holders.
DewPro® MMR31
Moisture Transmitter 
(Mid-Range, 1 or 2 Current Loops)
Installation & Operation Manual
A40251532 Rev.C
July 2020

ii
[no content intended for this page]

DewPro<Superscript>® MMR31 Installation & Operation Manual i
Information Paragraphs
Note: These paragraphs provide information that provides a deeper understanding of the situation, but is not
essential to the proper completion of the instructions.
IMPORTANT: These paragraphs provide information that emphasizes instructions that are essential to proper setup
of the equipment. Failure to follow these instructions carefully may cause unreliable performance.
CAUTION! This symbol indicates a risk of potential minor personal injury and/or severe damage to
the equipment, unless these instructions are followed carefully.
WARNING! This symbol indicates a risk of potential serious personal injury, unless these
instructions are followed carefully.
Safety Issues
WARNING! It is the responsibility of the user to make sure all local, county, state and national
codes, regulations, rules and laws related to safety and safe operating conditions are
met for each installation. The safety of any system incorporating the equipment is the
responsibility of the assembler of the system.
Auxiliary Equipment
Local Safety Standards
The user must make sure that he operates all auxiliary equipment in accordance with local codes, standards,
regulations, or laws applicable to safety.
Working Area
WARNING! Auxiliary equipment may have both manual and automatic modes of operation. As
equipment can move suddenly and without warning, do not enter the work cell of this
equipment during automatic operation, and do not enter the work envelope of this
equipment during manual operation. If you do, serious injury can result.
WARNING! Make sure that power to the auxiliary equipment is turned OFF and locked out before
you perform maintenance procedures on the equipment.
WARNING! It is the responsibility of the user to make sure the PWR, Hart, Modbus and I/O cable can
meet the cable specification, which is described in Appendix A.
Qualification of Personnel
Make sure that all personnel have manufacturer-approved training applicable to the auxiliary equipment.

ii DewPro<Superscript>® MMR31 Installation & Operation Manual
Personal Safety Equipment
Make sure that operators and maintenance personnel have all safety equipment applicable to the auxiliary
equipment. Examples include safety glasses, protective headgear, safety shoes, etc.
Unauthorized Operation
Make sure that unauthorized personnel cannot gain access to the operation of the equipment.
Environmental Compliance
Waste Electrical and Electronic Equipment (WEEE) Directive
Panametrics Measurement & Control is an active participant in Europe’s Waste Electrical and Electronic Equipment
(WEEE) take-back initiative, directive 2012/19/EU.
The equipment that you bought has required the extraction and use of natural resources for its production. It may
contain hazardous substances that could impact health and the environment.
In order to avoid the dissemination of those substances in our environment and to diminish the pressure on the
natural resources, we encourage you to use the appropriate take-back systems. Those systems will reuse or recycle
most of the materials of your end life equipment in a sound way.
The crossed-out wheeled bin symbol invites you to use those systems.
If you need more information on the collection, reuse and recycling systems, please contact your local or regional
waste administration.
Visit https://www.gemeasurement.com/environmental-health-safety-ehs for take-back instructions and more information
about this initiative.

DewPro<Superscript>® MMR31 Installation & Operation Manual iii
Contents
Chapter 1. General Information
1.1 Unpacking and Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
1.2 Model Number. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
1.3 Version Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4.1 First 4-20 mA Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4.2 Second 4–20 mA Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4.3 Polymer Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4.4 Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Chapter 2. Installation
2.1 Mounting the MMR31 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Using a Compression Fitting or a Flange. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Using a Bracket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Wiring Configurations with One Current Loop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.1 General Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.2 Normal Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.3 Environments with Severe Electrical Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.4 General Wiring Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Wiring Configurations with Two Current Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.1 General Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3.2 Normal Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
2.3.3 Environments with Severe Electrical Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
2.3.4 General Wiring Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
2.4 Selecting the Units of Measure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Chapter 3. Calibration and Troubleshooting
3.1 Calibration Using Two Saturated Salt Solutions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Calibration Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.1 Calibrating the Low RH Reading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.2 Calibrating the High RH Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
3.3 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.1 Loop Current is Out of Range. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.2 No Loop Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.3 Slow Response Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.3.4 Frozen Output Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Chapter 4. Optional Display/User Interface
4.1 Accessing the Programming Buttons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.1.1 Removing the Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.2 Programming the Matrix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.3 Matrix Buttons - Special Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3.1 Reset to “Normal” Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3.2 Display Only . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.3.3 Default Values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.4 Matrix Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.4.1 System Administration Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.4.2 Moisture Measurement Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.4.3 4-20 mA Output Range Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.4.4 Temperature Measurement Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.4.5 Error Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Chapter 5. Specifications
5.1 Technical Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2 Optional Onboard Display with User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.3 EMI/RFI Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
5.4 EMC Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
5.5 Available Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Contents
iv DewPro<Superscript>® MMR31 Installation & Operation Manual

DewPro<Superscript>® MMR31 Installation & Operation Manual 1
Chapter 1. General Information
Chapter 1. General Information
1.1 Unpacking and Inspection
Upon receipt of the DewPro MMR31, examine the shipping carton for broken or open packing, distortion, or any other
evidence of mishandling. If your inspection indicates damage to the unit or any of its components may have
occurred, notify the carrier within 15 days of delivery and request an inspection.
If no shipping damage is suspected, move the carton to a clean work area and unpack the contents. The carton you
received should contain:
• DewPro MMR31 Instrument
• Installation and Operation Manual
• Calibration Certificate
1.2 Model Number
Locate the product label on your MMR31, and compare the last five characters of the model number with the product
numbering structure shown on the next page. This will confirm that your MMR31 has been configured to your
specifications.
Figure 1: DewPro MMR31 Product Label

Chapter 1. General Information
2DewPro<Superscript>® MMR31 Installation & Operation Manual
1.2 Model Number (cont.)
1 2 3 4 5
MMR31 – R 2 A 1 S
1 - Certification
• R. Standard Certification (not certified)
• S. Other
2 - Process Connection
•1. 3” diameter galvanized floor flange with 12.7 mm (½” NPT-M) compression fitting
•2.3/4” NPT-M compression fitting
•3. 1/2” NPT-M compression fitting
•4. 3/4” x 16 “O” ring compression fitting (UNF thread)
•6. No mounting hardware
•8.G1/2 compression fitting (Male thread), gasket, SS ferrule
•S. Other
3 - Protective Cap
• A. Standard, with 100 micron sintered filter
• S. Other
4 - Enclosure Conduit
• 1. Enclosure Conduit M20 x 1.5-F with cable gland and plug
• 2. Enclosure Conduit M20 x 1.5-F with 1/2” FNPT adapter and plug
•S.Other
5 - Output Configuration/Dewpoint Range
•A.One output 4-20 mA selectable: RH 0-100% or dewpoint 15 to +85°C (5 to 185°F), absolute humidity, mixing
ratio, no display, fault status 22 mA
•B.Two 4-20 mA DC output loops: 1st loop Moisture, 2nd loop temperature –15 to +85°C (5 to 185°F),
no display, fault status 22 mA
•C. As A, fault status hold
•D. As A, fault status 3.6 mA
•E. As B, fault status hold
•F. As B, fault status 3.6 mA
•G. As A, with integral display, user interface
•H. As B, with integral display, user interface
•S.Other
1.3 Version Descriptions
The DewPro MMR31 mid-range moisture transmitter is available in two versions:
•One isolated 4-20 mA current loop: The loop current represents the selected moisture unit (see “Selecting the
Units of Measure” on page 14).
•Two isolated 4-20 mA loops: The second loop current represents temperature. A unique patented feature of
this version is that both loops can be powered by a single supply.

DewPro<Superscript>® MMR31 Installation & Operation Manual 3
Chapter 1. General Information
The MMR31 transmitter includes:
• Sensor element
• Stainless steel probe
• Weather-proof enclosure
• Microprocessor electronics
It is designed to be inserted directly into the process. Various mounting hardware, such as flange and compression
fittings are available for mounting into a duct, process chamber, wall, etc. The DewPro MMR31 measures relative
humidity in %, dew point temperature in °F or °C, absolute humidity in g/m3, or mixing ratio in g/kg. An optional
display with user interface allows the user to configure the MMR31 (see Chapter 4, “Optional Display/User Interface”
on page 19).
1.4 Theory of Operation
1.4.1 First 4-20 mA Loop
The MMR31 microcontroller-operated electronics operates with a voltage supply of 12 to 28 VDC. At the nominal
24 VDC supply, the maximum loop resistance is 600 ohms. The signal is represented by the 4 to 20 mA loop current
and is directly proportional to 0 to 100% relative humidity, or, if selected, the dew point temperature range of
5 to 185°F (-15 to +85°C), the absolute humidity in a range of 1 to 350 g/m3, or the mixing ratio in a range of
1 to 830 g/kg.
1.4.2 Second 4–20 mA Loop
The specifications for the first loop current are also valid for the second loop current, except that the 4 to 20mA signal
always corresponds to the temperature range of 5 to 185°F (-15 to +85°C).
1.4.3 Polymer Sensor
The sensing element in the MMR31 is a silicon-based polymer that uses the capacitance principle for the moisture
measurement. The IC chip includes the moisture sensor and appropriate integrated circuitry. A platinum RTD
temperature sensor is built in to provide temperature compensation for maximum accuracy. The sensor element is
protected from condensation using a hydrophobic sintered filter. An additional removable filter cap serves as a
pre-filter.
1.4.4 Calibration
Each MMR31 is factory-calibrated against precise NIST certified moisture references. Field calibration is possible with
the use of saturated salt solutions (refer to Chapter 3, “Calibration and Troubleshooting” on page 15).

Chapter 1. General Information
4DewPro<Superscript>® MMR31 Installation & Operation Manual
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DewPro<Superscript>® MMR31 Installation & Operation Manual 5
Chapter 2. Installation
Chapter 2. Installation
To properly install your MMR31, carefully follow the instructions in this chapter.
2.1 Mounting the MMR31
To select a suitable mounting location, refer to the dimensions shown in Figure 2 below.
11.73 [298]
4.47 [114]
0.79 [20]
0.50 [12.7]
5.56 [141] (w/display)
4.61 [117] (wo/display)
NOTE: Dimensions are inches [mm]
Compression Fittin
g
2.00 [50.8]
Ø3.00 [76.2]
Thread
(G1/2, 1/2" NPT-M, etc.)
Figure 2: MMR31 and Compression Fitting Dimensions
2.1.1 Using a Compression Fitting or a Flange
IMPORTANT: Be certain that the tip of the probe does not touch the inside wall of the pipe or container.

Chapter 2. Installation
6DewPro<Superscript>® MMR31 Installation & Operation Manual
IMPORTANT: A 1.4571 stainless steel ferrule is required for use in pressurized systems. Ensure that your probe has the
appropriate fitting for your application.
To monitor moisture inside a pipe or container, mount the probe using a compression fitting connection or a flange
(see Figure 3 below). Adjust the ferrule for a probe insertion length of at least 1 in. (25 mm) and tighten the
compression fitting as follows:
1. Hand-tighten the nut.
2. Use a wrench to tighten the nut 1-1/2 turns. When tightened in this manner, the fitting with a stainless steel ferrule
can withstand pressures up to 17 bar (250 psi).
Min. 1 in. (25 mm)
Figure 3: Mounting the Probe in a Pipe

DewPro<Superscript>® MMR31 Installation & Operation Manual 7
Chapter 2. Installation
2.1.2 Using a Bracket
The MMR31 can be used to monitor the air in a room or other such area, by using the available mounting kits shown in
Figure 4 below.
6.50 in.
(165 mm) 2.76 in.
(70 mm)
4.45 in.
(113 mm)
3.23 in.
(82 mm)
4.45 in.
(113 mm)
2.95 in.
(75 mm)
0.79 in.
(20 mm)
4.45 in.
(113 mm)
Panel Mounting Vertical Pipe Mounting
Horizontal Pipe Mounting Horizontal Pipe Mounting
Figure 4: Mounting Kit Configurations

Chapter 2. Installation
8DewPro<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/m3absolute 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

DewPro<Superscript>® MMR31 Installation & Operation Manual 9
Chapter 2. Installation
2.2.2 Normal Environments
A standard two-wire, stranded cable can be used in a normal environment to interconnect the MMR31 with its loop
power source.
2.2.3 Environments with Severe Electrical Noise
When the MMR31 is installed in environments with severe electrical noise, wiring must be done with shielded and
grounded cable, as shown in Figure 6 below. Details of the MMR31 testing and certifications in such environments can
be found in Chapter 5, “Specifications” on page 29, and the CE Declaration of Conformity at the end of this manual.
External Earth Ground
Connect the cable shield
Shielded Two-Wire
Cap
Cable
to the ground terminal
for maximum RFI protection
Figure 6: Shielded Cable Wiring Diagram

Chapter 2. Installation
10 DewPro<Superscript>® MMR31 Installation & Operation Manual
2.2.4 General Wiring Instructions
To wire the MMR31, refer to Figure 7 below and complete the following steps:
1. Unscrew the cap on the terminal side of the unit.
2. Loosen the cable gland located on the side of the unit.
3. Feed the cable through the conduit opening.
Note: Use a standard signal cable size.
4. Retighten the metal cable gland to meet IP 67 and to relieve any stress on the wire.
5. Connect the wires to the MMR31 terminals as shown in Figure 7 below.
6. Verify that a voltage between 12 and 28 VDC is present across the terminals marked + and –.
Note: This is the voltage that is actually measured across the MMR31 terminals. It is not necessarily exactly the
same as the power supply voltage, due to voltage loss in the wires, displays, indicators, etc.
7. To meet EMI/RFI immunity requirements, a two-wire shielded cable with a common foil shield layer is used to
power the MMR31. To clamp the shield foil in the metal cable gland, remove 3 in. (75 mm) of the insulation and
fold back the foil. The ground wire must be connected to the internal grounding screw.
GND LOOP 1
–+
+
–
24 VDC Nominal (12–28V)
External GND/SHIELD Connection
Internal GND Connection
Figure 7: Electrical Connections - One Current Loop

DewPro<Superscript>® MMR31 Installation & Operation Manual 11
Chapter 2. Installation
2.3 Wiring Configurations with Two Current Loops
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.
2.3.1 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/m3absolute humidity, 1 to 830 g/kg mixing ratio, or custom range corresponding to 4–20 mA. Figure 8
below illustrates a typical configuration.
The same general specifications apply to the second current loop. However, the range for the second current loop is
always 5 to 185°F (–15 to +85°C), corresponding to temperature, unless an optional display/user interface is used for
a custom range.
IMPORTANT: Be sure that the two current loops are connected independently. DO NOT install a jumper at the MMR31 +
and - terminals to power both current loops from a single power supply.
115/230 VAC
115/230 VAC
Figure 8: System Configuration with Display and Power Supply

Chapter 2. Installation
12 DewPro<Superscript>® MMR31 Installation & Operation Manual
2.3.2 Normal Environments
A standard two-wire, stranded cable can be used in a normal environment to interconnect the MMR31 with its loop
power sources.
2.3.3 Environments with Severe Electrical Noise
When the MMR31 is installed in environments with severe electrical noise, wiring must be done with shielded and
grounded cable, as shown in Figure 9 below. Details of the MMR31 testing and certifications in such environments can
be found in Chapter 5, “Specifications” on page 29, and the CE Declaration of Conformity at the end of this manual.
External Earth Ground
Connect the cable shield
Shielded Four-Wire
Cap
Cable
to the ground terminal
for maximum RFI protection
Figure 9: Shielded Cable Wiring Diagram