Spider DSA User’s Manual
74
For other types of sensors, measurements below 1 Hz are possible with the DC
coupling modes. It is recommended that the control sensors in Shock tests use DC
coupling.
The single-ended modes, which include IEPE, should be adequate for most
situations, and are best for EMI noise rejection. However, if a non-IEPE sensor is
used, and a ground loop problem occurs, then the input mode should be switched
to differential. If a differential input mode cannot be used, then the ground of the
controller should be tied to the sensor with a low-impedance conductor.
Matching Sensor Sensitivity to the Input Range
A special technique is used in CI products to achieve a very high dynamic range in
the input channels. This patented technology uses two A/D converters for each
input channel to achieve 130 to 160dB dynamic range. Refer to the 130dB
Dynamic Range CI whitepaper for more details.
With this technology, there is no need for multiple input range
settings and measurements can be made over the entire range
from a few microvolts to 20 volts. However, signal outputs from
sensors should be as large as possible without overloading the
input channels to maximize the signal to noise ratio. Too large of an input will
cause clipping and distortion.
Do not exceed the input range stated in the specifications, usually ±20 V. For
example, if you are doing a vibration measurement estimated to be 10 g RMS and
the peak value of the test is assumed to go 5 times its RMS level, the sensitivity of
the sensor should be smaller than 20V/50g-peak = 400 mV/g.
Choosing a sensor with too low sensitivity will cause the signals to be buried in
noise. In the example above, if you choose a 4 mV/g sensor, the useful signal will
be 100 times lower. The effect of noise sources such as EMI and ground loops will
be much greater and the data will be unusable.
For charge input, the two ranges are 10,000pC and 49,000pC. For example, if the
full charge range is 10,000 pC, you should choose a sensor that generates less
than 10,000 pC with the expected peak excitation. But the signal should not be
too small as to be buried in the noise.
Power Connection
The Spider-20 is powered by an interchangeable battery with DC charger
interface. The fully charged brand new battery lasts at least 6 hours in full
operation. The lithium battery has the limited life span and should be replaced at
certain time.
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