The D342 Dual Bistim Module provides a switching function allowing stimuli of alternating polarity to be presented to each of two preparations. It includes independent controls for stimulus polarity (Normal, Alternating or Reverse) of each channel as well as warning of a stimulus timing rate that is too-fast. The control and timing for the pulses is generated by selecting other modules from the D330 MultiStim range.
It should be noted that the unit works with mechanical relays that require a certain time to switch their polarity. The circuitry is designed so that the changeover command is taken (independently for each channel) from the end of each stimulus timing pulse so that the relay ‘moves’ when no stimulus is being applied. As with all mechanical devices, relays have a finite life. This is quoted as a minimum of 100,000,000 mechanical operations. If the relay was to ‘move’ whilst a stimulus was present, the contacts would wear-out much quicker than the mechanics. Therefore, the circuit will detect and warn the user if the ‘time-between’ stimuli pulses is less than 5ms. The user must ensure that this never happens.