A395 Linear Stimulus Isolator


All WPI stimulus isolators are designed to supply constant current because current threshold (not voltage) is the most quantitatively reproducible parameter for stimulation of nerve and muscle. Model A395 dispenses current reproducibly from its Output terminals; the amplitude being determined by the selected current RANGE and the input voltage. Current amplitude is “constant”, that is, load resistance independent, provided that the I x R (load) product does not exceed the available battery supply voltage. An audible alarm (the compliance alarm) will sound if I x R reaches this limit. Model A395 D can generate a voltage of 70 volts or more across its OUTPUT terminals. Thus, the user can be sure that the amplitude of the current will be as dialed as long as the voltage drop accross the load (stimulus electrode path) does not reach the magnitude of the supply voltage. The compliance alarm would then be heard. The user would then know that (a) too much current was dialed for a given load or (b) inter-electrode resistance was too high or the electrode circuit path was open (this is illustrated by the Q uick Instrument Test below). Model A395 generates an output current of arbitrary (user-defined) wave shape; DC, AC, pulse, and combinations thereof. Battery operated, and photoelectrically- isolated from the input voltage drive, the instrument regenerates output currents which are linearly proportional to the analog voltage waveforms provided by your D/A converter or signal generator (see diagram below). The A395 is ideally suited for data acquisition and stimulator generators. It can be easily daisy-chained for mutiple channel requirements.