When quantities of each transducer type are known a system can be selected that supports the overall channel count, the excitation requirements and the specific transducers that are to be used. Issues include the use of constant voltage or constant current excitation, transducer calibration, availability of remote excitation sensing and the ability to monitor excitation levels.
Selection of other parameters such as analog bandwidth, filter cutoff frequency and sampling rate are dependent upon expected signal frequencies and signal waveshape. Are they basically sinusoids or are they square waves or other complex shapes?
Measurement accuracy is dependent upon a number of factors including gain and zero stability with time and temperature changes, linearity, crosstalk between channels and noise. Discussions of common-mode voltages sometimes cause eyes to glaze over but resultant errors are real. The ability of a system to minimize the effects of common-mode voltages is referred to as Common Mode Rejection Ratio, expressed in dB. This ratio defines the effect a common-mode signal at the input has on the system output. A single ended input has no common-mode rejection; these voltages are simply added to signal inputs so differential inputs are required for high performance data acquisition. Some error sources are dependent upon amplifier gain and filtering making a single, overall specification difficult to assign. An error budget can be determined by combining errors under specific conditions. Application Note 505 offers a method of predicting uncertainty.