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:

(

)

y

Sensitivit

g

V

V

on

Accelerati

out

out

0

−

=

[g]

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.

0 g position

−1 g position

+1 g position