www.murata-ps.com
ACM20 Series
Four-Function AC Power Meters
PRODUCT OVERVIEW
Murata Power Solutions’ ACM20 series AC power meters display the most critical
measurements 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 two input ranges: 0-32A
(with 0.01A resolution, 9999 watts max.); 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 true-rms voltage and current
values of triangle waves, square waves, and other irregularly shaped waveforms, with an
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, labora-
tory instrumentation, alternative energy applications, and any other products that require
precise monitoring of AC power.
Actual size
C
®
US E156931
FEATURES
Displays AC Volts, Amps, Watts, and Power Factor or Hertz
Two display modes: continuous auto cycling or fixed
Universal 85-264Vac (47-63Hz) operating range
(Measurement Category II)
Built-in current transformers simplify installation; choice of
32A or 100A ranges
Ideal for power distribution units (PDUs) and power strips
True-rms readings of complex voltage and current waveforms
Low-power consumption: less than ¼watt from 120Vac
One-piece polycarbonate housing fits ‘0U’ & ‘1U’ racks
Surface mount design occupies minimal panel space
Bright red LED-display with four annunciators
Optional Frequency reading models (0.1Hz resolution)
Approvals to UL/CSA/IEC/EN 61010-1
SIMPLIFIED SCHEMATIC DIAGRAM
VOLTS
LOAD CURRENT
+5V
L1
AMPS
WATTS
PF
A/D
CONVERTER
+5V
B
85-264 Vac
47-63 Hz
+5V
AC/DC
CONVERTER
MICRO-
CONTROLLER
A
For full details go to
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SEL
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30 Apr 2010 MPM_ACM20 Series.A06
Page 1 of 6
ACM20 Series
Four-Function AC Power Meters
Performance/Functional Specifications
Typical at TA=+ 25ºC, 120Vac @ 60Hz, unless otherwise noted
Measurement Limits
AC Voltage
AC Current, 32A models
➀
AC Current, 100A models
➀
Active Power: 32A models
Active Power:
100A models
Frequency
Power Factor
Overcurrent Rating
➁
Performance
Sampling Rate
Voltage Accuracy
➂
Current Accuracy
➂
Power Accuracy
➂
Frequency Accuracy
➂
Power Factor Accuracy
Measurement Bandwidth
Temperature Drift (0 to 60ºC)
Zero-Current Reading (within 2 sec.)
Zero-Power Reading (within 2 sec.)
Supply Voltage (TB1) (Measurement Category II)
All Models – 47-63 Hz
Supply Current
➃
All Models
Power Supply Terminal Block
Wire Size
Insulation Strip Length
Screw Tightening Torque
Rated Voltage
Display
Display Type and Size
Overrange Indication
Decimal Point Selection
Physical/Environmental
Operating Temperature
Storage Temperature
Humidity (non-condensing)
Dimensions
Weight: 32A models
Weight:
100A models
Hex Nut Tightening Torque
0
–40
0
–
–
–
+60
+75
85
°C
°C
%
4 Digit LED, 9.14mm (0.36in) high
Flashing ‘9999’ Watts
➄
Automatically Set
16-22AWG, solid or stranded
6.4mm (0.250 in)
0.4Nm (3.6 lb-in)
300Vac
35
50
110
mA
85
120
264
Vac
2-3 samples / sec
±1%
±1%
±2%
±0.1
±3%
140Hz (Voltage), 14kHz (Current)
0.5 Counts/ºC
0.00
0
Amps
Watts
Hz
Min.
85.0
0.00
0.0
0
0
47.0
.00
Typ.
-
-
-
-
-
-
1.00
Max.
264.0
32.00
100.0
9999
26.4
63.0
-
Units
Volts
Amperes
Amperes
Watts
kW
Hz
-
ACM20-4-AC1-R-C
ACM20-5-AC1-R-C
ACM20-4-AC1-R-F-C
ACM20-5-AC1-R-F-C
100A, 85-264Vac Supply (Power Factor Reading)
32A, 85-264Vac Supply (Power Factor Reading)
100A, 85-264Vac Supply (Frequency Reading)
32A, 85-264Vac Supply (Frequency Reading)
ORDERING INFORMATION
TECHNICAL NOTES
1.5 x rated full-scale current
!
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 multi-function 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, WATTS, power factor (PF), or
line frequency on ‘-F’ HERTZ models.
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.
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.
See mechanical specifications
1.3oz (37.9g)
1.5oz (43.5g)
0.14 N-m (20 ozf-in)
➀
Specified full-scale currents are those passing through the power meter’s built-in current
transformer’s primary load-circuit.
➁
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 guaranteed up to
the rated current.
➂
ACM20 Power Meters are calibrated with near full-scale 60Hz sine-wave inputs.
➃
All specified maximum supply currents are steady state; larger surge currents can occur at
initial application of line power.
➄
Applies to 32A model only.
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30 Apr 2010 MPM_ACM20 Series.A06
Page 2 of 6
ACM20 Series
Four-Function AC 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 applica-
tion-mandated requirements pertaining to the user’s specific installa-
tion.
5. Supply Fusing, and Grounding:
ACM20 power meters are not inter-
nally fused. If supply fusing is required it must be externally installed
according to the supply wire’s maximum amperage rating. No con-
nection is required to earth/chassis ground.
ACM20 power meters draw minimal steady-state supply currents
(110mA max.), and in most applications can be fused according to the
supply wire’s maximum amperage rating. However, these models can
draw significantly higher surge currents for brief periods when the ac
line voltage is initially applied to TB1.
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.
TYPICAL WIRING DIAGRAMS
120 V
LOAD
Epoxy encapsulation
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.
Polarity dot on bottom
B
A
TB1
H
N
120 Vac (50/60 Hz)
Figure 1. Wiring diagram for 110/120V single phase systems
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30 Apr 2010 MPM_ACM20 Series.A06
Page 3 of 6
ACM20 Series
Four-Function AC Power Meters
TYPICAL WIRING DIAGRAMS, CONT.
220 V
LOAD
Epoxy encapsulation
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.
Polarity dot on bottom
B
A
TB1
L1
L2
220 Vac (50/60 Hz)
Figure 2. Wiring diagram for 220/240V systems with no neutral
220 V
LOAD
Epoxy encapsulation
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.
Polarity dot on bottom
B
A
TB1
L1 Neutral L2
220 Vac (50/60 Hz)
Figure 3. Wiring diagram for 220/240V systems with neutral (monitoring L1)
220 V
LOAD
Epoxy encapsulation
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.
Polarity dot on bottom
B
A
TB1
L1 Neutral L2
220 Vac (50/60 Hz)
Figure 4. Wiring diagram for 220/240V systems with neutral (monitoring L2)
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30 Apr 2010 MPM_ACM20 Series.A06
Page 4 of 6
ACM20 Series
Four-Function AC Power Meters
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.
PANEL
ACM20
2-56 Hex Nuts (4 places)
Tighten each nut to 15 to 20 ozf-in (0.106 to 0.140 N-m).
Panel Cutout
L1
SIDE VIEW
Figure 5. Panel Installation
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.
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30 Apr 2010 MPM_ACM20 Series.A06
Page 5 of 6
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