www.murata-ps.com
DCM20 Series
Three-Function DC Power Meters
PRODUCT OVERVIEW
Murata Power Solutions’ DCM20 series DC power meters display the most critical measurements in DC-powered equipment: voltage, amperage and power. A front panel selectorswitch provides two modes of operation: a fixed reading of any of the three parameters, or
a continuous cycling through all three measurements. In fixed-reading mode, the function
to be displayed (V/A/W/kW) is selected by a capacitive touch sensor, avoiding the wear-out
issues often seen with membrane or other mechanical control switches.
The DCM20 typically requires 6 mA of operating current at a supply voltage of 12 VDC, and
only 2 mA at 72 VDC. This feature allows it to be added to existing systems with minimal
electrical loading effects.
FEATURES
Displays DC volts, amperes, watts and kilowatts.
Two display modes: continuous auto cycling or fixed.
9 - 72 VDC voltage operation.
0.5 - 72 VDC voltage measurement range.
0 -1200 A current measurement range (dependent on
external shunt).
0 - 96 kW power measurement range.
Supports both high-side and low-side current monitoring.
Long-life contactless touch-sensor function selector
switch.
Low current consumption (< 10 mA at 12 VDC).
Internal self-resetting fuse
One-piece polycarbonate housing fits ‘0U’ & ‘1U’ racks.
Compact surface mount design occupies minimal panel
space.
Bright LED-display with four function annunciators.
Choice of red, green, or blue display.
SIMPLIFIED SCHEMATIC DIAGRAM
CURRENT-LIMITED
EXTERNAL POWER SOURCE
For full details go to
www.murata-ps.com/rohs
9 – 72
+
+
VDC
–
EXTERNAL
SHUNT
TB1
1
+V
2
–V
3
+IN
4
–IN
–
THERMAL
FUSE
The DCM20 can be powered from a DC power supply ranging from 9 to 72 VDC. The meter
supports two fundamental voltage measurement configurations. In the first configuration,
the DCM20 is powered from the DC power supply line which it is monitoring. When used in
this way, it can provide voltage measurements in the range of 9 - 72 VDC, as it is unpowered at lower voltages. The DCM20 may also be configured such that it is powered from a
separate power supply than that which is monitoring. When used in this way, it can support
voltage measurements over the entire 0.5 to 72 VDC range.
For current and power measurements, DCM20 series DC power meters require the use of
an external shunt resistor. The DCM20’s wide common-mode input range (0 to 72 V) supports both high-side and low-side current sensing in a variety of applications. A 4-position
DIP switch supports field selection of 16 shunt calibration factors. Additionally, a 12-turn
trim potentiometer is also provided on the rear of the meter to support precision field
calibration of the meter to the actual shunt value.
A large (0.36 in/9.2 mm), bright LED display makes DCM20 DC power meters easily
readable from as far as 15 feet (5 meters). All units are packaged in a one-piece, vibration
resistant, polycarbonate housing that can be installed in 0U rack components and vertical
rack spaces as small as 1U. Their miniature size is perfect for laboratory instrumentation,
alternative energy applications, standby power supplies and any other products that require
precise monitoring of DC voltage, current, and power.
DCM20
DC-DC
CONVERTER
J1
3
2
1
+
–
SIGNAL
CONDITIONER
Figure 1. Simplified Schematic
+5 V
–5 V
ADC
(VOLTAGE)
ADC
(CURRENT)
SHUNT TRIM
ADJUST
DISPLAY
VOLTS AMPS WATTS kW
MICROCONTROLLER
SHUNT RANGE
SELECTOR SWITCH
SEL
TOUCH
SENSOR
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MPM_DCM20Series.A01.D5 Page 1 of 6
Performance/Functional Specifications
Typical at TA = +25ºC , V+ = 12 VDC unless otherwise specified
Measurement Limits Min Typ Max Units
DC Voltage
DC Current
Range ‘1’ - 10 mΩ external shunt
Range ‘16’ – 41.67 µΩ external shunt-5-1200
Current Shunt Differential Voltage
Range
Current Shunt Common-mode Voltage
Range
Current Fine Trim Range using Trim
Potentiometer
Power
Watts Display Mode
Kilowatts Display Mode
Performance
Display Update Rate 2.5 updates/sec.
Voltage Accuracy ± 1% ± 2%
Current Accuracy ± 2% ± 3%
Power Accuracy ± 2% ± 3%
Temperature Drift (0 - 60) +/- 0.5 Counts/°C
Zero Current Reading (within 1 sec.) +/- 4 Count
Operating Supply Voltage 9 72 V DC
Operating Supply Current
12 V operation
72 V operation
Display
Display Type and Size
Over-range Indication Flashing Display
Decimal Point Selection Automatically Set
TB1 Terminal Block
Wire Size
Insulation Strip Length 6mm (0.24 in)
Screw Tightening Torque 4.6 in - lb (0.51 N-m)
Physical/Environmental
Operating Temperature 0 +60 °C
Storage Temperature -40 +75 °C
Humidity (non-condensing) 0 85 %
Dimensions See figure 6
Weight
Hex Nut Tightening Torque 20 in - oz (0.14 N-m)
(A) Voltage measured across +V (TB1-1) and –V (TB1-2) OR +IN (TB1-3) and –V (TB1-2) terminals.
(B) Current measurement range dependent on external shunt selection.
Applied to +IN (TB1-3) and –IN (TB1-4) terminals.
(C)
Voltage applied across +IN (TB1-3) and –V (TB1-2) terminals.
(D)
Current drawn by +V (TB1-1) terminal when operating voltage applied across +V (TB1-1) and
(E)
–V (TB1-2) terminals.
(A) 0.5 V 72 V DC
(C)
(D)
(B)
-100 +100 mV DC
0 72 V
±1%
0
0
(E)
4 Digit LED, 9.14 mm (0.36 in) Height
4 LED Annunciators (‘Volts,’ ‘Amps,’
Unit Weight: 1.02 oz / 29g
Net Package Weight: 12.28 oz / 348g
Gross Package Weight: 22.05 oz / 625g
5
1200
999996W DC
6
10
2
5
‘Watts,’ ‘kW’)
Copper Wire
14-24 AWG
A DC
kW DC
% Full-
scale
mA
ORDERING INFORMATION
DCM20-1-DC5-R-C (Red Display)
DCM20-1-DC5-G-C* (Green Display)
DCM20-1-DC5-B-C* (Blue Display)
*Consult factory for availability
DCM20 Series
Three-Function DC Power Meters
TECHNICAL NOTES
IMPORTANT! To ensure safe and reliable operation, DCM20 power
meters must be installed and serviced by qualified technical personnel.
!
Contact Murata Power Solutions if there is any doubt regarding their
installation or operation.
1. Measurement Type: DCM20 series multifunction DC power meters
employ precision ADCs and a low-power microcontroller to measure and
display DC voltage, current and power. The choice of measurement is
selectable through the front panel. The meters measure DC current using
an external series shunt resistor which is inserted into the circuit to be
measured. Because the DCM20 has a wide common-mode input range
(0 - 72 VDC), the shunt resistor may be inserted into either the high-side
(supply) or the low-side (return) of the circuit being monitored.
DC Voltage may be monitored either at the meter’s +IN (TB1-3) input
terminal or at the meter’s +V (TB1-1) power input terminal, based on
the setting of jumper block J1. The choice of voltage monitoring input is
selected based on the application requirements.
The DCM20 derives its DC power measurement by multiplying the
measured current by the measured voltage. Power is always reported
as a positive quantity, regardless of the polarity of the measured current.
(Power = | Voltage × Current | ).
2. Basic Operation: Upon first application of power to the meter, the unit
will first perform a self-test routine and then continuously display DC
volts with the VOLTS LED annunciator illuminated. The display will remain
in the VOLTS mode as long as the front panel ‘SEL’ button is not touched.
After the unit powers up to normal operation in the VOLTS reading mode,
momentarily (approximately one second) touching the ‘SEL’ button on
the unit’s front panel twice in succession will cycle the display to AMPS,
and then to WATTS (or kW, depending on the power measurement value).
Momentarily touching ‘SEL’ a third time will return the display back to
the VOLTS reading mode. Holding the ‘SEL’ button down for 5 seconds
will place the unit in a continuous auto-cycling mode, and the display will
repetitively scroll through all three measurements, with each measurement remaining displayed for 3 seconds.
When the continuous auto-cycling mode is initially selected, the unit will
briefly display ‘Auto On’ before continuous cycling begins. Momentarily
touching the ‘SEL’ button again will cause the unit to briefly display ‘Auto
OFF’ before it returns to the fixed VOLTS reading mode.
The power-up default display mode (Volts/Amps/Watts/Auto-cycle) may
be selected by simply leaving the DCM20 in a given display mode for 60
seconds or more. The next time the meter powers up, it will do so in the
new default mode. The default mode may be reset by selecting a new
operating mode and leaving the meter in that mode for 60 seconds or
longer.
3. Calibration: The DCM20’s voltage measurement function is factorycalibrated and cannot be field-calibrated. Because the meter is designed
to work with a wide range of shunt resistors for current measurement,
however, field configuration and fine adjustment of the current measurement function is supported. The DCM20’s shunt scaling factor is selected
by a 4-position DIP switch SW1 on the rear of the unit (refer to figure 9,
Mechanical Specifications). A total of 16 ranges are supported. Table 1
lists supported current ranges and their associated switch settings, and
also includes recommended Murata shunt resistors for selected ranges.
Additionally, a trimmer potentiometer on the rear of the unit supports fine
adjustment of the shunt scaling factor to accommodate tolerance errors
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MPM_DCM20Series.A01.D5 Page 2 of 6
DCM20 Series
Three-Function DC Power Meters
in the shunt value. Because adjusting the meter using this potentiometer
requires that the DCM20 be powered up and measuring current, this
operation should only be performed by qualified personnel using an
insulated adjustment tool.
Table 1. Shunt Range Selection
Range SW1 Setting
1
1
1
2
1
3
1
4
1
5
1
6
1
7
1
8
1
9
1
10
1
11
1
12
1
13
1
14
1
15
1
16
Full-scale
Current
Range (A)
Full-scale
Power
Range
5.000 400.0 W 50 3020-01097-0
10.00 800 W 100 3020-01107-0
20.00 1600 W 50 3020-01098-0
50.00 4000 W 50 3020-01096-0
50.00 4000 W 100 --
75.00 6000 W 50 --
100.0 8000 W 50 3020-01099-0
100.0 8000 W 100 3020-01108-0
150.0 2.00 kW 50 3020-01100-0
200.0 6.00 kW 50 3020-01101-0
300.0 24.00 kW 50 3020-01102-0
400.0 32.00 kW 50 --
500.0 40.00 kW 50 3020-01103-0
800.0 64.00 kW 50 3020-01104-0
1000 80.00 kW 50 3020-01105-0
1200 96.00 kW 50 3020-01106-0
Shunt
Voltage
(mV)
Recommended
Murata Shunt
Resistor P/N
4. Shunt Selection: Table 1 lists recommended current shunts avail-
able from Murata Power Solutions for current ranges supported by the
DCM20. Please note that a given shunt may not necessarily support
continuous operation at the extreme limits of its measurement range.
The maximum current that a shunt may be safely operated at is also
highly dependent on application conditions such as ambient temperature,
airflow and mounting position. Before selecting and installing a shunt,
you should refer the shunt’s datasheet for details on correct operation.
5. Jumper Configuration: The setting of jumper J1 determines the source
of voltage to be measured. When the shorting block is placed over posts
J1-1 and J1-2, the DCM20 measures the voltage between the +IN (TB1-
3) connector terminal and the -V (TB1-2) connector terminal. When the
shorting block is placed over posts J1-2 and J1-3, the DCM20 measures
the voltage between the +V (TB1-1) and -V (TB1-2) connector terminals.
The meter must have the shorting block placed on jumper J1 for normal
operation. Jumper block J1 is located on the rear of the meter as shown
in figure 9 (mechanical drawing). The DCM20 is shipped with the shorting
block placed across jumper pins J1-2 and J1-3.
6. Wiring: Power supply and input wiring must be rated for the electrical
and environmental conditions under which the meter will be operated.
They must also comply with any regulatory or application-mandated
requirements pertaining to the user’s installation. Connections to DCM20
meters must be made with all power sources de-energized. Refer to the
Functional Specifications section for detailed wire type and wire gauge
information.
Wiring insulation should be stripped to 6 mm (0.24 in). All wires must be
inserted into the terminal block openings such that the screw terminal
does not pinch any insulation. After final assembly, inspect all terminal
block connections for shorts between adjacent conductors; this step is
particularly important when using stranded wire.
7. Protection and Fusing: DCM20 meters’ power supply leads are protected against momentary overvoltage ((+V - -V) > 72 V) and reverse polarity
conditions ((+V - -V) < 0 V ). The +V (TB1-1) power supply line is also
protected with an internal self-resetting thermal fuse. The meter’s +IN
(TB1-3) and –IN (TB1-4) terminals are protected against brief voltage
transients. Neither set of inputs is protected against sustained conditions
exceeding the limits listed in in the Performance & Functional Specifications table. External fusing must be supplied by the user in accordance
to applicable safety and regulatory requirements for the system in which
the DCM20 is installed.
8. Shunt Polarity: While the external current shunt has no intrinsic ‘polarity’, the way in which it is connected into the circuit being measured will
influence the polarity of current as measured by the meter. The relationship between current direction and meter reading is shown in figure 2.
SHUNT VOLTAGE
+ –
–IN+IN
VOLTS AMPS WATTS kW VOLTS AMPS WATTS kW
METER READS
POSITIVE AMPS
Figure 2. Relationship between shunt voltage polarity
and meter reading
SHUNT VOLTAGE
– +
METER READS
NEGATIVE AMPS
–IN+IN
9. Terminal Block Wire Size & Torque Ratings: It is important to tighten
all screw-terminals to their torque specification of 4.5 in - lb (0.51 N-m).
Proper tightening will help ensure reliable operation. Applications subject
to vibration should use stranded wire.
10. Typical Wiring Diagrams: The DCM20 is a flexible voltage, current, and
power measurement device, supporting both high-side and low-side
shunt configurations. This section describes four of the most common
ways in which the DCM20 may be used.
In figure 3, the current shunt is inserted into the load’s positive supply
line, which is known as high-side measurement. The DCM20 is also
powered from this line. In this configuration the shorting block on jumper
J1 should be connected across pins J1-1 and J1-2. Because the meter
is powered from the line being monitored, useful measurements can
only be made on DC line voltages in the range of 9 - 72 VDC, as at lower
voltages the meter will not be powered. In this configuration, the DCM20
measures the sum of both the load power and the power dissipated by
the shunt.
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MPM_DCM20Series.A01.D5 Page 3 of 6
DCM20 Series
Three-Function DC Power Meters
DCM20
LOAD
TB1
1
2
3
J1
4
123
+
DC
SUPPLY
9 - 72 VDC
–
+V
–V
+IN
–IN
– –+ +
SHUNT
Figure 3. High-side current measurement, meter powered from DC line
Figure 4 shows the case where current is also measured at the high-
side of the load but the meter is powered from an independent supply.
Because the meter is now independently powered, it can now measure
voltage and power over the full range of 0.5 to 72 VDC. In this configuration the shorting block on jumper J1 should be connected across pins
J1-1 and J1-2 so that the meter measures the voltage at the +IN (TB1-3)
terminal. In this configuration, the meter measures the sum of both the
load power and the power dissipated by the shunt resistor.
LOAD
TB1
DCM20
1
2
3
4
J1
123
+
METER
SUPPLY
9 - 72 VDC
LOAD
SUPPLY
72 V MAX
–
–
+
+V
–V
+IN
–IN
– –+ +
SHUNT
Figure 4. High-side current measurement, independent meter supply
Figure 5 shows a high-side shunt configuration in which the power
dissipated by the shunt is excluded from the measurement. In this case,
the meter’s +V (TB1-1) terminal is connected to the -IN (TB1-4) terminal
and the meter both derive power and the voltage measurement from
this point in the circuit. Measuring voltage through the +V (TB1-1) pin
requires that the shorting block be connected across pins J1-2 and J1-3
of jumper J1. Because the meter requires very little operating power, its
addition to the load will typically influence neither the current nor power
measurements to a significant degree.
Figure 6 shows a configuration where the shunt is inserted into the
load return line and measures the current through that connection. In
this case, the meter must be powered from the DC line though the +V
(TB1-1) input, as the +IN (TB1-3) input only detects the voltage across
the shunt (< 100 mV). For this reason the jumper shorting block should be
placed across pins J1-2 and J1-3 of jumper J1 to enable measurement of
voltage from the +V (TB1-1) input. The total power reported in this configuration is the sum of the load power plus the shunt power dissipation.
DCM20
TB1
LOAD
1
2
3
J1
4
123
+
–
–V
+
POWER
SUPPLY
9 - 79 VDC
–
+V
+IN
–IN
–
+
SHUNT
Figure 5. High-side current measurement, shunt power excluded
POWER
SUPPLY
9 - 72 VDC
SHUNT
LOAD
+
–
+
–
+V
–V
+IN
–IN
+
–
TB1
DCM20
1
2
3
4
J1
123
Figure 6. Low-side current measurement
Table 2. J1 Jumper Settings*
Measurement Configuration Figure
Voltage
Measured at . .
High-side current measurement 3 +IN (TB1-3) 1-2
High-side current measurement,
independent meter supply
High-side current measurement,
shunt power excluded
4 +IN (TB1-3) 1-2
5 +V(TB1-1) 2-3
Low-side current measurement 6 +V (TB1-1) 2-3
*Product shipped with jumper across pins 1 and 2.
Jumper
Across Pins
11. Noisy Power Supplies: Some power supplies contain high-frequency
switching devices that may conduct and/or radiate significant noise onto
the low-level signal developed across the internal shunt. Even though
DCM20 ammeters incorporate built-in input filtering, some portion of this
noise may be amplified and subsequently measured by its sensitive input
circuitry. The amplified noise introduces errors that are particularly noticeable at zero load current (i.e., the ammeter function may not display
a relatively steady “000” reading). Connecting an external, non-polarized
capacitor across the +IN and -IN inputs can help reduce noise-related
display errors. In certain situations, the use of twisted pair or shield wiring may be required. As a general rule, avoid using excessively long leads
between the shunt and the meter’s +IN (TB1-3) and –IN (TB1-4) inputs.
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MPM_DCM20Series.A01.D5 Page 4 of 6
PANEL INSTALLATION
3
3
2
1
THIRD ANGLE PROJECTION
Rear View
SW1
ON
JP1
TB1
R4
4
2
1
2
3
1
(Current Trim)
4
41.301.626
Centered
1.070 27.18
Centered
2-56-UNC-2A Studs (4)
Bottom View
0.40 10.1
Side View
0.51 13
0.35 8.9
Front View
2.10 53.3
1.43 36.3
Components are shown for Ref Only
DCM20 Series
Three-Function DC Power Meters
All connections to DCM20 power meters must be made after the unit is
The installed wire-positions should be such that minimal mechanical
Using figure 7 as a guide, carefully insert the DCM20 assembly into the
PANEL INSTALLATION
securely attached to the panel and with all associated load and supply
voltages de-energized (off), using extreme caution and observing all
safety measures applicable to the user’s installation.
forces are applied to TB1 or to the DCM20 power meter itself. In highvibration environments, it is strongly recommended that adequate strain
reliefs be used for all wiring.
panel opening. From the rear of the panel, install and then tighten the
Mounting Panel
DCM20 Panel Meter
#2 Flat Washer (4)
#2 Lock Washer (4)
2-56 Hex Nut (4)
Torque each nut to 15-20 in - oz
[0.106-0.140 N-m]
four #2-56 hex nuts over the threaded studs. Tighten each nut to 15 to
20 in - oz (0.106 to 0.140 N-m). Use only the factory-supplied hardware
as the use of substitute hardware could result in an unsafe installation
and/or adversely affect the reliability of the installation.
The recommended range of panel thickness that can be used with
the supplied hardware is 0.040 in (1.0 mm) to 0.25 in (6.4 mm). Panel
thicknesses outside of this range may require additional user-supplied
hardware or modifications. Refer to the panel cutout drawing (figure 8)
for recommended drill and cutout dimensions.
PANEL CUTOUT
41.301.626
C
L
22.230.875
4x 0.093±0.003 2.36±0.08
C
1.070
L
27.18
Figure 7. Panel installation
1. Description of safety marks:
Caution, risk of electrical shock
Caution, risk of danger
Equipment is protected throughout by double or reinforced insulation
2. Cleaning Instructions: Gently clean with dry cloth only.
3. Caution: if the equipment is used in a manner not specified by Murata Power Solutions, the protection provided by the equipment may be impaired.
Panel Cutout
Figure 8. Recommended panel cutout dimensions
Dimensions are in Inches [mm]
Tolerances (Unless Otherwise Specified)
2 Place 0.02 [0.5]
0.010 [0.25]3 Place
37.471.475
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MPM_DCM20Series.A01.D5 Page 5 of 6
MECHANICAL SPECIFICATIONS
DCM20 Series
Three-Function DC Power Meters
36.3
1.43
0.40 10.1
2.10 53.3
Front View
2-56-UNC-2A Studs (4)
Side View
41.301.626
Centered
0.51 13
0.35
8.9
THIRD ANGLE PROJECTION
Components are shown for Ref Only
Dimensions are in Inches [mm]
Tolerances (Unless Otherwise Specified)
2 Place 0.02 [0.5]
0.010 [0.25]3 Place
Murata Power Solutions, Inc.
ISO 9001 and 14001 REGISTERED
www.murata-ps.com/support
Bottom View
Figure 9. Mechanical specifications
Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply
the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without
notice. © 2018 Murata Power Solutions, Inc.
SW1
ON
1
2
3
4
JP1
2
1
3
R4
(Current Trim)
TB1
4
3
2
1
1.070 27.18
Centered
Rear View
This product is subject to the following operating requirements
and the Life and Safety Critical Application Sales Policy:
Refer to: http://www.murata-ps.com/requirements/
MPM_DCM20Series.A01.D5 Page 6 of 6
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