Murata Power Solutions’ ACM20 series AC power meters display the most critical measure-
ments in mains-powered equipment: voltage, amperage, active power (watts), and power
factor. A front panel selector-switch provides two modes of operation: a fixed reading of
any of the four parameters, or a continuous cycling through all four measurements. An
optional model displays line frequency with 0.1Hz resolution. All ACM20 multi-function
power meters include built-in current transformers—no other user-supplied components
are required.
ACM20 series AC power meters are available in a choice of three input ranges: 0-10A (with
0.001A resolution, 999.9 watts max.); 0-32A (with 0.01A resolution, 9999 watts max.); and
0-100A (0.1A resolution, 26.4kW max.). An 85-264Vac (47-63Hz) operating supply range
makes these power meters perfect for worldwide power monitoring applications. And,
unlike conventional, average-responding products, ACM20 power meters can accurately
display the real power and true-rms current values of triangle waves, square waves, and
other irregularly shaped waveforms, with a typical accuracy of ±1% of full scale.
Their large (0.36"/9.2mm), bright red LED display makes ACM20 AC 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 vertical ‘0U’ and ‘1U’ rack spaces.
Their miniature size is perfect for UPS power sources, power strips, laboratory instrumenta-
tion, alternative energy applications, and any other products that require precise monitoring
of AC power.
PRODUCT OVERVIEW
FEATURES
n
Displays AC Volts, Amps, Watts, and Power Factor or Hertz
n
Two display modes: continuous auto cycling or fixed
n
Universal 85-264Vac (47-63Hz) operating range
(Measurement Category II)
n
Built-in current transformers simplify installation; choice of
10A, 32A, or 100A ranges
n
Ideal for power distribution units (PDUs) and power strips
n
True-rms readings of complex voltage and current waveforms
n
Low-power consumption: less than ¼watt from 120Vac
n
One-piece polycarbonate housing fits ‘0U’ & ‘1U’ racks
n
Surface mount design occupies minimal panel space
n
Bright red LED-display with four annunciators
n
Optional Frequency reading models (0.1Hz resolution)
n
Approvals to UL/CSA/IEC/EN 61010-1
SIMPLIFIED SCHEMATIC DIAGRAM
A
B
85-264 Vac
47-63 Hz
AC/DC
CONVERTER
CURRENT
LIMITED
SUPPLY
MICRO-
CONTROLLER
SEL
+5V
+5V
+5V
A/D
CONVERTER
LOAD CURRENT
L1
VOLTS AMPS WATTS PF
Actual size
C
®
US E156931
New!
Low-Wattage
Models
Available
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ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 1 of 7
Measurement Limits Min. Typ. Max. Units
AC Voltage 85.0 - 264.0 Volts
AC Current, 10A models (1)
AC Current, 32A models (1)
AC Current, 100A models (1)
0.00
0.00
0.0
-
-
-
9.999
32.00
100.0
Amperes
Amperes
Amperes
Active Power: 10A models
Active Power: 32A models
Active Power: 100A models
0
0
0
-
-
-
999.9
9999
26.4
Watts
Watts
kW
Frequency 47.0 - 63.0 Hz
Power Factor .00 1.00 - -
Overcurrent Rating (2) 1.5 x rated full-scale current
Performance
Sampling Rate 2-3 samples / sec
Voltage Accuracy (3) ±1%
Current Accuracy (3) ±1%
Power Accuracy (3) ±2%
Frequency Accuracy (3) ±0.1 Hz
Power Factor Accuracy ±3%
Measurement Bandwidth 140Hz (Voltage), 14kHz (Current)
Temperature Drift (0 to 60ºC) 0.5 Counts/ºC
Zero-Current Reading (within 2 sec.) 0.00 Amps
Zero-Power Reading (within 2 sec.) 0 Watts
UL/IEC61010-1 Measurement category II
Supply Voltage (TB1) (Measurement Category II)
All Models – 47-63 Hz 85 120 264 Vac
Supply Current (4)
All Models 35 50 110 mA
Power Supply Terminal Block
Wire Size 16-22AWG, solid or stranded
Insulation Strip Length 6.4mm (0.250 in)
Screw Tightening Torque 0.4Nm (3.6 lb-in)
Rated Voltage 300Vac
Display
Display Type and Size 4 Digit LED, 9.14mm (0.36in) high
Overrange Indication Flashing ‘9999’ Watts (5)
Decimal Point Selection Automatically Set
Physical/Environmental
Operating Temperature 0 +60 °C
Storage Temperature –40 +75 °C
Humidity (non-condensing) 0 85 %
Dimensions See mechanical specifications
Weight: 32A models
Weight: 100A models
1.3oz (37.9g)
1.5oz (43.5g)
Hex Nut Tightening Torque 0.14 N-m (20 ozf-in)
(1) Specified full-scale currents are those passing through the power meter’s built-in current
transformer’s primary load-circuit.
(2) The overcurrent rating of 1.5 x the rated full-scale current is a continuous rating and
applies to the current passing through the built in current transformer. Accuracy is guaran-
teed up to the rated current.
(3) ACM20 Power Meters are calibrated with near full-scale 60Hz sine-wave inputs.
(4) All specified maximum supply currents are steady state; larger surge currents can occur at
initial application of line power.
(5) Applies to 10A and 32A models only.
Performance/Functional Specifications
Typical at TA=+ 25ºC, 120Vac @ 60Hz, unless otherwise noted
ORDERING INFORMATION
See page 7 for all active part numbers and descriptions.
TECHNICAL NOTES
IMPORTANT! To ensure safe and reliable operation, ACM20 power
meters must be installed and serviced by qualified technical person-
nel. Contact Murata Power Solutions if there is any doubt regarding
their installation or operation.
1. Measurement Type: ACM20 series multifunction AC power meters
employ a precision energy metering integrated circuit and a low-
power microcontroller to measure and display the rms voltage and
current, active (real) power, power factor (or line frequency on ‘–F’
suffix models) of ac mains supplies from 47-63Hz. Please note,
ACM20 power meters use the voltage present at their TB1 terminal
block and the secondary current of their built-in current transformer
L1 to calculate and then display VOLTS, AMPS, WATTS, power factor
(PF), or line frequency on ‘-F’ HERTZ models.
While the ACM20 displays the rms value of line voltage and line
current, the VOLTS reading has an upper limit of 140Hz (-3db point),
which means rectangular-shaped voltage waveforms, and waveforms
with sharp transitions, will read lower than their true-rms value. For
example, a square wave line voltage will read approximately 1-2%
lower, a triangle wave will read 3% lower, and a modified sine wave
will read 18% lower. The oscillograms on page seven illustrate typical
ACM20 VOLTS readings when powered from four ac waveforms.
The 140Hz bandwidth limit does not apply to the WATTS reading nor
to the AMPS reading. The circuitry used for these two measurements
has an upper bandwidth of 14kHz. ACM20 power meters are mains
operated devices designed to measure ac currents and voltages,
within the specified limits previously noted. DC currents and voltages
will not be measured accurately.
2. Basic Operation: Upon application of ac power to TB1, the unit will
first perform a self-test routine and then continuously display ac 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 three times in succession will cycle
the display to AMPS, WATTS, and end at PF (or HERTZ for ‘–F’ mod-
els). Momentarily touching ‘SEL’ a fourth time will return the display
back to the VOLTS reading mode.
Holding the ‘SEL’ button down for 3 seconds will place the unit in a
continuous auto-cycling mode, and the display will repetitively scroll
through all four 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. Mo-
mentarily touching the ‘SEL’ button again will cause the unit to briefly
display ‘Auto OFF’ before it returns to the fixed VOLTS reading mode.
!
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ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 2 of 7
Displaying a specific mode on power up: Units manufactured after
February 2012 can be configured to automatically show any one
of the four display modes upon future applications of ac power. For
example, it may be desirable to configure the unit to always power up
in the AMPS mode.
To set the unit to always read AMPS on power up, tap the SEL switch
until the AMPS mode is displayed, and then leave the unit in this mode
for at least 60 seconds. As long as the SEL switch is not pressed
again during the 60 second interval, the unit will configure itself to
always power up displaying the chosen mode, which is AMPS in this
example.
In summary, operating the unit undisturbed in a particular display
mode for 60 seconds or longer will automatically configure the unit
to display that particular mode the next time ac power to the unit is
cycled off and back on. This functionality also applies to the auto-
cycle mode, that is, the unit can be configured to always power up in
the auto-cycle (scrolling) display mode by following the instructions
outlined above.
3. Calibration: Due their digital design, ACM20 power meters cannot be
calibrated in the field. ACM20 power meters are factory-calibrated to
meet their specified accuracies with the supplied L1 current trans-
former. Use of any other current transformer will produce significant
errors for the Amps, Watts, and Power Factor measurements.
Contact Murata Power Solutions if additional information is required
regarding calibration, setup, or any other technical issue pertaining to
ACM20 power meters.
4. Wiring: All power supply wiring must be rated for the voltages and
currents they will carry and must comply with any code or application-
mandated requirements pertaining to the user’s specific installation.
5. Supply Fusing, and Grounding: Wires specified in the Functional
Specifications section must be used for making connections to
ACM20 series power meters. No connection is required for earth/
chassis ground.
TYPICAL WIRING DIAGRAMS
H N
B
A
TB1
120 Vac (50/60 Hz)
120 V
LOAD
Epoxy encapsulation
Polarity dot on bottom
Fuse*
Figure 1. Wiring diagram for 110/120V single phase systems
ACM20 series power meters are not internally fused. Terminal block
TB1 is to be used only for powering the power meter's internal circuitry;
it must not be used to supply power to external loads. The supply wires
feeding these power meters must be fused with a 0.5A/250V time
delay/time lag fuse, in accordance with applicable regulatory codes.
Wire insulation must be stripped to within ±10% of the stated dimen-
sions, and wires should be inserted into TB1 such that their insulation
is not pinched by the screw terminal.
6. Current Transformer Polarity: In order to perform accurate Watts
and Power Factor measurements, connections to the two rear power
supply inputs, TB1-A and TB1-B, and built-in current transformer L1
must have the proper polarity. That is, the load current flowing in the
wire passing through L1's center hole must have the same polarity as
the line voltage connected to TB1-A and TB1-B.
The wiring diagrams in Figures 1-4 ensure that, for a purely resistive
load, current flowing in current transformer L1’s primary circuit will
have the same polarity as the applied voltage at TB1. If proper polarity
is not followed, the Watts and Power Factor readings will be zero. To
correct a zero Watts reading, simply reverse the direction of the load
wire passing through the hole in L1.
7. Connector Torque Ratings: It is important to tighten TB1’s, screw-
terminals to their rated torque specification of 3.6 pound-inches
(0.4Nm). Proper tightening will minimize connector losses and ensure
safe, reliable operation.
8. Isolation: Except for the 2-56 thread metallic mounting studs, all of
the ACM20 power meter’s internal components (printed circuit board,
resistor, capacitors, current transformer L1’s secondary leads, etc.)
are at the ac-mains potential connected to TB1. ACM20 power meters
are designed to measure and be powered from one ac power-source
only. Any other connection schemes will introduce significant mea-
surement errors.
Note: If the ACM20 displays zero Watts with
power applied to the load, reverse the direction
of the wire passing through the CT's center hole.
See Technical Note 6 for more information.
*See technical note 5.
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ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 3 of 7
TYPICAL WIRING DIAGRAMS, CONT.
L1 L2
220 V
LOAD
B
A
220 Vac (50/60 Hz)
TB1
Ep
oxy encapsulation
P
olarity dot on bottom
Fuse*
Figure 2. Wiring diagram for 220/240V systems with no neutral
Figure 3. Wiring diagram for 120/240V systems with neutral (monitoring L1)
L1 Neutral L2
120 V
LOAD
B
A
220 Vac (50/60 Hz)
TB1
Fuse*
Ep
oxy encapsulation
P
olarity dot on bottom
Figure 4. Wiring diagram for 120/240V systems with neutral (monitoring L2)
L1 Neutral L2
120 V
LOAD
B
A
220 Vac (50/60 Hz)
TB1
Fuse*
Ep
oxy encapsulation
P
olarity dot on bottom
Note: If the ACM20 displays zero Watts with
power applied to the load, reverse the direction
of the wire passing through the CT's center hole.
See Technical Note 6 for more information.
Note: If the ACM20 displays zero Watts with
power applied to the load, reverse the direction
of the wire passing through the CT's center hole.
See Technical Note 6 for more information.
Note: If the ACM20 displays zero Watts with
power applied to the load, reverse the direction
of the wire passing through the CT's center hole.
See Technical Note 6 for more information.
*See technical note 5.
*See technical note 5.
*See technical note 5.
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ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 4 of 7
PANEL INSTALLATION
All connections to ACM20 power meters must be made after the unit
is securely attached to the panel and with all associated load and
supply voltages de energized (off), using extreme caution and observ-
ing all safety measures applicable to the user’s installation.
Care should be exercised when passing conductors through the
power meter’s built-in current transformer L1. The installed wire-
positions should be such that minimal mechanical forces are applied
to current transformer L1, TB1, or to the ACM20 power meter itself.
In high-vibration environments, it is strongly recommended that
adequate strain reliefs be used for all wiring.
Using Figure 5 as a guide, carefully insert the ACM20 assembly into
the panel opening. From the rear of the panel, install and then tighten
the four #2-56 hex nuts over the threaded studs. Tighten each nut to
15 to 20 ozf-in (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 inches (1.0mm) to 0.25 inches (6.4mm).
Panel thicknesses outside of this range may require additional user-
supplied hardware or modifications. Front panel space permitting,
ACM20 power meters will fit most existing ACA-20RM / ACA-20PC
ammeter cutouts, allowing for easy upgrading of existing installations.
Figure 5. Panel Installation
SIDE VIEW
2-56 Hex Nuts (4 places)
Tighten each nut to
15 to 20 ozf-in (0.106 to 0.140 N-m).
L1
ACM20
Panel Cutout
PANEL
PANEL CUTOUT
RECOMMENDED DRILL AND PANEL CUTOUT DIMENSIONS
INTERNAL CORNER RADII:
0.032 (0.81) MAX.
1.07
(27.18)
0.838* - 0.870
(21.29* - 22.10)
1.336* - 1.426
(33.93* - 36.22)
1.626 (41.30)
0.093 (2.362) DIAMETER (4 REQUIRED)
* The two dimensions marked with an * specify the
minimum recommended panel cutout opening for
ACM20 power meters. Space permitting, the larger
dimensions noted (0.87in., and 1.426in.) should be
used. The panel opening must be centered vertically
and horizontally between the four 0.093 (2.362mm)
diameter holes.
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.
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ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 5 of 7
MECHANICAL SPECIFICATIONS
OSCILLOGRAMS
The graphs below show typical ACM20 power meter VOLTS readings when the unit is powered from four common ac-voltage waveforms.
V O LT S
AC POWER METER
AMPS WAT T S
SEL
PF
1.43
(36.3)
2.10 (53.3)
Front View
Back View
0.51
(12.95)
1.07
(27.20)
0.40
(10.16)
0.12 (3.05) (min)
0.12 (3.05) (min)
Side View
1.63
(41.4)
0.086 DIA (REF)
2-56 UNC THREAD
0.33 (8.39)
(min)
0.22 (5.59)
(min)
0.60
(15.24)
(max)
Bottom View
B
A
TB1
L1
Diameter:
10A and 32A models: 0.35 (8.9)
100A models: 0.57 (14.5)
CT Lead Length:
Standard: 2.0” (50.5mm) min.
32A blue LED model: 20.0” (500mm) min.
100A blue LED model: 28.0” (710mm) min.
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ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 6 of 7
ORDERING INFORMATION
ACM20-2-AC1-R-C 10A, 85-264Vac Supply (Power Factor Reading)
ACM20-5-AC1-R-C 32A, 85-264Vac Supply (Power Factor Reading)
ACM20-4-AC1-R-C 100A, 85-264Vac Supply (Power Factor Reading)
ACM20-2-AC1-R-F-C 10A, 85-264Vac Supply (Frequency Reading)
ACM20-5-AC1-R-F-C 32A, 85-264Vac Supply (Frequency Reading)
ACM20-4-AC1-R-F-C 100A, 85-264Vac Supply (Frequency Reading)
ACM20-5-AC1-B-20-C 32A, 85-264Vac Supply (Power Factor Reading), 20 inch lead length
ACM20-4-AC1-B-28-C 100A, 85-264Vac Supply (Power Factor Reading), 28 inch lead length
ACM20-4-AC1-B-C 100A, 85-264Vac Supply (Power Factor Reading)
ACM20-5-AC1-G-F-C 32A, 85-264Vac Supply (Frequency Reading)
www.murata-ps.com/support
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.
Murata Power Solutions, Inc.
ISO 9001 and 14001 REGISTERED
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/
ACM20 Series
Four-Function AC Power Meters
MPM_ACM20 Series.D02 Page 7 of 7