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REGULATORY STANDARDS
The harmonized, international regulatory standard relating to the safety of nerve and muscle stimulators is IEC 601-2-10. Certain stimulation equipment is excluded from this standard, such as stimulators intended for cardiac defibrillation; however, for the purposes of defining relevant safety metrics for STMISOC/D/E stimulus isolation adapters this standard is quite relevant.
STMISOC/D/E units are designed in such a manner that the power available to stimulate the subject is limited. This limitation of power is achieved through the use of a stimulus isolation transformer that has physical constraints (due to its size and construction) which absolutely in accordance to known physical laws constrain the maximum transferable power to be no more than a specific level.
Section 51.104 of the IEC 601-2-10 standard clearly specifies the limitation of output power for a variety of wave types.
* For stimulus pulse outputs, the maximum energy per pulse shall not exceed 300 mJ,when applied to a load resistance of 500 ohms.
* For stimulus pulse outputs, the maximum output voltage shall not exceed a peak value of 500 V, when measured under open circuit conditions.
STMISOC/D/E units employ a stimulus isolation transformer that limits the output pulse width to 2 ms maximum, under 500 ohm load conditions. In addition, the highest available output voltage is 200 V pk-pk under open circuit conditions.
Maximum pulse energy calculation:
Watts (instant max) = (200 V x 200 V) / 500 ohms = 80 W
Joules (Watts x Seconds) = 80 W x 0.002 seconds = 0.16 Joules = 160 mJ
Accordingly, the highest possible energy output using the STMISOC/D/E is 160 mJ. The maximum available energy from STMISOC/D/E stimulus isolation adapters is limited to be considerably less than the 300 mJ maximum as specified by IEC 601-2-10. |
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