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Don’t distort the figures

Less filtering lowers noise levels. By Peter Peisker.

The typically noisy environment for industrial applications such as flow metering, or temperature, pressure or gas analysis, where only a small sensor signal of around 200mV exists, means noise influence on the sensor cable can easily reach the amplitude of the sensor signal. To combat this, increasingly higher resolution data acquisition devices at faster speeds are being developed.

The major trade off that hardware designers face is to find a balance between highest resolutions, while still achieving enough feedback speed for fast process control. Typical high performance applications include sampling signals from several probes in the KHz range up to 18bits or more. This should be no problem so long as the signal is large enough. Full scale ranges of most analogue/digital converters are in the range of +/-2.5V, therefore it is hard to compensate for noise without reducing sampling rate in order to achieve highest resolution.

Comparing available types of data converters, sigma delta is the only architecture capable of offering a resolution of up to 24bits and implementing techniques that reject noise interference, especially in the 50 to 60Hz range.

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Graham Pitcher

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