The D342 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.
The module connects to the outputs of a D333 or D343 via 2mm-2mm leads (supplied). The D333/343 has the function and specifications as defined in its specification. Each module is preset for specific channels whose outputs are to be switched. Normally, the unit will be supplied preset for channels 1 and 2 or as required when a full system is purchased. That is, the timing signals of the D333/343 and the D342 will automatically by the same. The channels set is shown at the top of the module front panel.