ACA-20RM-ALM Datasheet, PDF (3/5 Pages) Murata Power Solutions Inc. – True-rms-AC Ammeters with Alarm Function

To adjust the overcurrent alarm set-point level:
A. Turn off power to the ACA-20RM-ALM (i.e., the power source con-
nected to TB1).
B. Carefully remove the shorting jumper across JP1 from its ‘normal
operation position’ across terminals 2 and 3 and place it across JP1
terminals 1 and 2.
C. Re-apply power to TB1 and, using a plastic insulated adjusting tool,
adjust R3 so the ammeter’s display shows the desired overcurrent
trip level in Amps.
D. Turn off power to the ACA-20RM-ALM and return JP1’a shorting
jumper back to its ‘normal operation position’ across terminals 2
and 3. Re-apply power to TB1 to resume normal operation. If pos-
sible, after the ammeter is re-configured for normal operation, the
load current should be slowly increased to verify the visual alarm
operates when the load current exceeds the preset level.
Please note, the load circuit does not need to be turned off to adjust the
overcurrent alarm set point. Current flowing through L1 while JP1 is
across terminals 1 and 2 will not be measured. Once tripped, the alarm
set point function has a hysteresis of approximately 0.5A.
The overcurrent alarm function can also be adjusted with JP1 in its
normal operation position if the desired alarm overcurrent-level is
actually flowing through L1 (i.e., with a live load). For example, with
a 20 Amp load current flowing through L1, and with JP1 in its normal
operation position, slowly adjust R3 until the display starts flashing on
and off. Using this “live load” adjustment method eliminates the need
to turn off power to TB1 or reconfiguring JP1.
4. Wire Gauges and Fusing: Wires specified in the Functional Specifica-
tions section must be used for making connections to ACA-20RM-ALM
Series ammeters. All power-supply and load wiring must be rated for
the supply voltages and currents they will conduct and must comply
with any code or application-mandated requirements pertaining to the
user’s specific installation.
The supply wires connected to both the ammeter and the load must be
fused according to the current rating of the wire gauge being used, in
accordance with applicable regulatory codes. Also, wire insulation should
be stripped to within +/–10% of the stated dimensions, and wires should
be inserted into TB1 such that their insulation is not pinched by the screw
terminal. TB1 is to be used only for powering the meter’s internal circuitry,
it must not be used to supply current to external loads.
All models draw minimal steady-state supply currents (50mA max.),
and in most applications, they can be fused according to the supply
wire’s maximum amperage rating. However, these products can draw
significantly higher surge currents for brief periods when the ac line
voltage is initially applied.
5. AC Supply Polarity and Grounding: The two supply inputs, TB1-A and
TB1-B, on ACA-20RM-ALM ammeters are not in themselves polarity
sensitive, that is, they have no internal “AC LO” or “AC HI” designa-
tions. ACA-20RM-ALM ammeters do not include or require a connec-
tion to earth/chassis ground.
ACA-20RM-ALM Series
True-rms-AC Ammeters with Alarm Function
6. 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.
7. Isolation: The built-in current transformer L1 provides a minimum
of 2000Vdc isolation between the load conductor and the ammeter’s
supply voltage connected to TB1.
8. Split-Core CT (Clamp-on) Models: Both 50A models feature a split-
core current transformer that can be clamped around a properly insu-
lated live conductor without having to disconnect or remove power
from the load circuit. This live-connection capability can only be used
if the load’s power source is electrically isolated (see technical note
7) from the ammeter’s own power source that’s connected to TB1.
The ammeter’s ac power supply must always be denergized before
making connections to TB1. Refer to the ‘Panel Installation’ section of
this data sheet for additional information.
BACK VIEW
A
FUSED AC POWER
TB1
B
L1
TO AC LOAD
Figure 2. Typical wiring diagram
BACK VIEW
TB1
JP1
3
2
1
R7
CAL
R3
ALARM
3 _JP1
2 _{Normal Operation}
1
3 JP1
2 Overcurrent
1 Alarm Adjustment
Figure 3. Alarm circuit component location
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