PR electronics PRetop 5335 - Page 32

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3. The entity concept.
Equipment that is FM-approved for intrinsic safety may be connected to barriers
based on the ENTITY CONCEPT. This concept permits interconnection of approved
trans mitters, meters and other devices in combinations which have not been
specifically exam ined by FM, provided that the agency’s criteria are met. The com-
bination is then intrinsically safe, if the entity concept is acceptable to the authority
having jurisdiction over the installa tion.
The entity concept criteria are as follows:
The intrinsically safe devices, other than bar riers, must not be a source of power.
The maximum voltage U
i
(Vmax) and current I
i
(Imax), and maximum power
P
i
(Pmax), which the device can receive and remain intr insically safe, must be equal
to or greater than the voltage (U
o
or Voc or V
t
) and current (I
o
or Isc or I
t
) and the
power P
o
which can be delivered by the barrier.
The sum of the maximum unprotected capaci tance (C
i
) for each intrinsically safe
device and the interconnect ing wiring must be less than the capacitance (C
a
)
which can be safely connected to the barrier.
The sum of the maximum unprotected inductance (L
i
) for each intrinsically safe
device and the interconnect ing wiring must be less than the inductance (L
a
) which
can be safely connected to the barrier.
The maximum entity parameters U
i
, I
i
, P
i
, C
i
, and L
i
for the Pretop 53xx Transmit-
ters are listed on pages 1 and 2 of this document.
The entity parameters U
o
,Voc or V
t
and Io,Isc or I
t
, and C
a
and L
a
for barriers are
provided by the barrier manufac turer.
2001-10-04 5300Q502 Rev. AB 3/3