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This
current sensor from Pololu is a carrier for Allegro’s ACS714LLCTR-05B-T
Hall effect-based linear current sensor, which
operates at 5V and
has an output sensitivity of 185 mV per A. The
current sensor board features:
- Bidirectional measurement from -5 to 5 V
(though the
robust
sensor IC can survive up to five times the overcurrent condition).
- The
sensor's conductive path internal resistance is typically
1.2 mΩ (just over 1/1000 of an ohm), and the PCB
is made with 2-oz copper, so very little power is
lost in the board.
- Use
of a Hall effect sensor means the IC is able to electrically isolate
the current path from the sensor’s electronics (up to 2.1 kV RMS). This means it can be used
anywhere along the current path, and still offfers good electrical
isolation!
- 80 kHz bandwith that can optionally be
decreased
by adding a capacitor across the board pins marked “filter”.
- High
accuracy and reliability. With a typical total output error of 1.5%
(at room
temperature with factory calibration), an extremely stable output
offset
voltage, and almost zero magnetic hysteresis.
- Automotive
grade operating temperature range of -40°C –
150°C.
The sensor requires a supply voltage of 4.5 – 5.5 V
to be connected across the Vcc and GND
pads, which are labeled on the bottom silkscreen. The sensor outputs an
analog voltage that is linearly proportional to the input current. This
output voltage is centered at 2.5 V and changes by
185 mV per amp of
input current, with positive current increasing the output voltage and
negative current decreasing the output voltage.
The input current can be connected to the board in a variety
of ways. For low-current applications, you can solder 0.1" male header
pins
to the board via the small through-holes on the input-current side of
the board. For higher-current applications, you can solder wires
directly to the through-holes whose sizes best match your wires, or you
can use solderless ring terminal connectors, as shown in the picture to
the right. The large through-holes are big enough for #6 screws.
Mounting information
The
board has two mounting holes on the logic side of the board. These
mounting holes are 0.5" apart and are designed for #2 screws.
Filtering the output
The
IC has an internal filter resistance of 1.7 kΩ, and the
carrier board
includes a 1 nF filter capacitor, which produces a low-pass RC
filter
with a 90 kHz cutoff. You can improve sensing system accuracy
for
low-frequency sensing applictations by adding a capacitor in parallel
with the integrated 1 nF capacitor across the pads marked
“filter” on
the bottom silkscreen (this capacitor is labeled C2b in the schematic
below). The frequency F that the filter will
attenuate to half its original power is given by:
F = 1 / (2πRC) = 1 / (11kΩ * (1 nF + Cf))
where Cf is the value of the capacitor
added to the filter pads.
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