AC Coupling DCCoupled Accelerometers Tech Note 403
Applications such as shock testing where very low frequency (sub-hertz) signal components are unimportant may wish to convert DC-coupled outputs to AC-coupled outputs. AC-coupling eliminates the 2.5 V bias and any bias drift errors, but cannot be used in inertial or tilt sensing applications. If the input of the measurement equipment is known to be stable and has a high impedance (≥10MΩ), each axis of the accelerometer can be AC-coupled with a capacitor and resistor as shown in the following diagram:
Recommended Configuration for AC Coupling
The low frequency roll-off based upon the capacitor and resistor values is:
π The capacitor must be a good quality non-polar with low leakage, such as monolithic ceramic. The capacitance value should be less than 10μF and its tolerance should be kept in mind when selecting. Resistor values should be below 1MΩ using metal film if possible. Some specific cutoff values based upon common capacitors and resistors are: C
R
Approx Cutoff
μF
kΩ
Hz
1.0 1.0 2.2 2.2 3.3 3.3
470 1,000 470 1,000 470 1,000
0.34 0.16 0.15 0.07 0.10 0.05
The above technique should be used with controlled cabling to high-impedance measurement equipment. Active conversion circuitry may be required when varying equipment, connections, or impedances are used, as these can shift the low-frequency pole.
TN 403: AC Coupling DC-Coupled Accelerometers precisionsensors.meas-spec.com
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7/23/2013 www.meas-spec.com