Invariants to time shift transforms and the law of energy conservation 
of biosignal representations are matched to conditions of biotechnical 
systems are use to active biomedical investigations. 
The effectivity of the biotechnical system had been understood as its 
informativity and non-invasiveness is increased. In the mathematical model 
of biosignal the Weber-Fehner law and the periodically correlation stochastic 
were taking into account. Conditions of an optimal filtration of biosignals 
are evoked under very low excitation of a biosystem with the biotechnical 
system is discussed. Valid causes for choice of the criterion of the 
informativity are grounded. Examples of applications of results for 
low excitation electroretinography systems are given.