MPM_ACA-20RM-ALM.A01 Page 2 of 5

ACA-20RM-ALM Series

True-rms-AC Ammeters with Alarm Function

www.murata-ps.com

TECHNICAL NOTES

IMPORTANT! To ensure safe and reliable operation, ACA-20RM-

ALM ammeters must be installed and serviced by qualified

technical personnel. Contact Murata Power Solutions if there is

any doubt regarding ammeter setup, installation, or operation.

1. Measurement Type: ACA-20RM-ALM ac ammeters employ a

true-rms input circuit to measure current flowing through L1. Stated

accuracy specifications are measured using a sine-wave current

at, or close to, the ammeter’s full-scale input range, at nominal line

frequency of 60Hz.

2. Calibration (Potentiometer R7): Periodic recalibration of ACA-

20RM-ALM ammeters is not required under normal, indoor operating

environments. If user calibration is necessary, it must be performed

by qualified technical personnel. Calibration is performed with poten-

tially lethal voltages applied to the ACA-20RM-ALM and its associated

wiring. A plastic, fully-insulated adjusting tool must be used to access

the calibration potentiometer R7 located on the back of the ammeter

(see ‘Mechanical Specifications’ section). Contact MPS if additional

information is required regarding calibration, setup, or any other

technical issue pertaining to ACA-20RM-ALM ammeters.

3. Overcurrent Alarm Setup and Adjustment (Potentiometer R3):

ACA-20RM-ALM ammeters feature a user-settable, overcurrent visual

alarm indication which can be used to alert operators that a load cir-

cuit breaker or fuse is approaching an overload condition. When the

load current sensed by L1 exceeds this preset level, the ammeter’s

LED display will flash from normal intensity to dim intensity at rate of

approximately 1.5 times per second.

As shown in Figure 3, the alarm circuit consists of jumper JP1, and

adjustment potentiometer R3. As shipped, R3 is factory set to trip

when the load current is approximately 24 Amps for 30A models, and

approximately 45 Amps for 50A models. When R3 is set to its maxi-

mum clockwise position, the alarm indication will not activate until the

load current flowing through L1 exceeds the maximum rating of the

ammeter, i.e., above 30.0A, or above 50.0A, depending on the model.

Performance/Functional Specifications

Specified full-scale currents are those passing through the ammeter’s built-in

current transformer’s primary load-circuit. See Notes 2 and 3 below for ad-

ditional model-specific information.

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 only,

it does not apply to any external circuit-wiring or external loads. Accuracy is

guaranteed up to the rated current level.

Specified accuracy applies to inputs with crest factors (CF) up to 2.0, where CF

= Vpeak/Vrms. Crest factors of 2 to 5 introduce an additional error of ±3% of full

scale. Ammeters are calibrated with a near full-scale 60Hz sine-wave current

flowing through the ammeter’s built-in CT.

All specified maximum power supply currents are steady state; larger surge

currents can occur at initial application of line power.

Rated Full-Scale Current

Min.

Typ.

Max.

Units

ACA-20RM-4-ACX-RL-ALM

—

—

50.0

Amperes

ACA-20RM-5-ACX-RL-ALM

—

—

30.0

Amperes

Overcurrent Rating

1.5 x Rated Full-Scale Current

Performance

Sampling Rate

2.5 Samples per second

Accuracy

±0.4%FS ±3 Counts with 60Hz

Sine-Wave Input

Measurement Type

rms Responding, Crest Factors of 1-5

Temperature Drift (0 to 60 °C)

—

±0.2

±0.4

Counts/ºC

Zero-Current Reading (within

30 sec.)

–001

000

001

Counts

Dielectric Withstanding Voltage

2000

—

—

Vdc

Power Supply Voltage

ACA-20RM-X-AC3-RL-ALM

85

120

140

Vac/47-63Hz

ACA-20RM-X-AC4-RL-ALM

170

220

264

Vac/47-63Hz

Power Supply Current

ACA-20RM-X-AC3-RL-ALM

—

30

50

mA/47-63Hz

ACA-20RM-X-AC4-RL-ALM

—

30

50

mA/47-63Hz

Alarm Function

Display indication

Flashing Display with actual current

reading and display intensity change

Settable range

ACA-20RM-4-ACX-RL-ALM

13

45

50

Amps

ACA-20RM-5-ACX-RL-ALM

8

24

30

Amps

Power Supply Terminal Block

Wire Size

16-22AWG, Solid or stranded

Insulation Strip Length

0.250 inches

Screw Tightening Torque

3.6 pounds-inches (0.4Nm)

Rated Voltage

310Vac

Display

Display Type and Size

3½ Digit Red LED, 0.37”/9.4mm High

Overrange Indication

“1___”

Decimal Point

Fixed, model dependent

(see full-scale input current)

Physical/Environmental

Operating Temperature

0

—

+60

°C

Storage Temperature

–40

—

+75

°C

Humidity (non-condensing)

0

—

85

%

Dimensions

Model dependent, see page 4 & 5

Weight

ACA-20RM-4-XXX-XX-ALM

1.5 Ounces (43 grams) nominal

ACA-20RM-5-XXX-XX-ALM

2.1 Ounces (60 grams) nominal

Ordering Information

ACA-20RM-4-AC3-RL-ALM-C

50.0A Range (split-core CT), 85-140Vac power

ACA-20RM-4-AC4-RL-ALM-C

50.0A Range (split core CT), 170-264Vac power

ACA-20RM-5-AC3-RL-ALM-C

30.0A Range, 85-140Vac power

ACA-20RM-5-AC4-RL-ALM-C

30.0A Range, 170-264Vac power