SCA720-D01
Murata Electronics Oy 9/13
www.muratamems.fi Doc. nr. 82171500 Rev.A
2. Functional Description
2.1. Measuring directions
2.2. Voltage to acceleration conversion
Analog output can be transferred to acceleration using the following equation for conversion:
ySensitivit
gVV
onAccelerati
outout
0−
=
[g]
where: V
out
(0g) = nominal output of the device at 0g position with 5 V supply voltage (ratiometric
output), Sensitivity is the sensitivity of the device and V
out
is the output of the sensor.
2.3. Ratiometric Output
Ratiometric output means that the zero offset point and sensitivity of the sensor are proportional to
the supply voltage. If the SCA720 supply voltage is fluctuating the SCA720 output will also vary.
When the same reference voltage for both the SCA720 sensor and the measuring part (A/D-
converter) is used, the error caused by reference voltage variation is automatically compensated
for.
2.4. Selftest and failure detection modes
To ensure reliable measurement results the SCA720 has continuous interconnection failure and
calibration memory validity detection. A detected failure forces the output signal close to power
supply ground or VDD level, outside the normal output range.
The calibration memory validity is verified by continuously running parity check for the control
register memory content. In the case where a parity error is detected, the control register is
automatically re-loaded from the EEPROM. If a new parity error is detected after re-loading data
analog output voltage is forced to go close to ground level (<0.25 V).
The SCA720 also includes a separate self test mode. The true self test simulates acceleration, or
deceleration, using an electrostatic force. The electrostatic force simulates acceleration that is high
enough to deflect the proof mass to the extreme positive position, and this causes the output signal
to go to the maximum value. The self test function is activated by a separate on-off command on
the self test input.
position
position
position
V
out,nom
= 2.5 V
