CoCo-80 User Manual
95
Built-In Digital Integration
Ideally a measurement is made using a sensor that directly measures the desired
quantity. For example an accelerometer should be used to measure acceleration,
a laser velocimeter or velocity pickup should be used to measure velocity and an
LVDT should be used to measure position. However since position, velocity and
acceleration are related by the time derivatives it should be possible to measure
an acceleration signal and then compute the velocity and position by
mathematical integration. Alternatively you can measure position and compute
velocity and acceleration by differentiating. The integration can be performed at
the analog hardware level or at the digital level.
The CoCo provides a means to digitally integrate or double integrate the incoming
signals. The integration module fits into the very first stage after data is digitized,
as shown below:
CoCo
Analog
Signal
Conditioning
A/D
Converter
(Optional)
High-Pass Filter
and Integration
Data
Conditioning
Spectral
Analysis
There are several issues to address in such implementation:
The integration and double integration algorithm has to be accurate enough and it
must find a way to reduce the effects of a DC offset. A tiny initial value, offset in
the measurement or temperature drift before the integration, may result in a huge
value after single or double integration. This DC effect can be removed using a
high-pass filter.
The initial digital signal must have a high signal to noise ration and high dynamic
range. The integration process in essence will reduce the high frequency energy
and elevate the low frequency components. If the original signals do not have
good signal noise ratio and dynamic range, the signals after integration and
double integration will have too much noise to use. The noise will corrupt the
integrated signal.
The instrument must be able to set two different engineering units: one
engineering unit for the input transducer and a second engineering unit after the
integration. For example, first the instrument must provide a means to set the
sensitivity of the sensor, say 100mV/g. After the double integration the
instrument must have the means to set the engineering unit to a unit that is
compatible with the integration such as mm.
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