Models 5843, 5844, 5843S and 5844S
RS-232 or TTL
3-
2
Single-mode:
19 dB of optical budget is typically available and is essentially consistent for
fiber diameters.
3.2.1.2
Fittings
Adding additional splices, feed throughs, or patches to the FOC will add losses
to the available optical budget. When using multi-mode Fiber Optic Cable
terminated and supplied by DYMEC, optical connector losses can be ignored
because the cable is tested after the terminations are added. If you are using
fittings not supplied by DYMEC, you can get the optical budget loss information
from their manufacturer(s).
3.2.1.3 Aging
As FOC ages, tiny cracks will form in the glass core of the fiber. These will
cause the attenuation of the cable to increase. The optical emitters age over
time causing a reduction in their optical launch power.
DYMEC suggests that a buffer be applied to the optical budget to assure proper
operation of the unit over a 20-year life. A 2.5 dB to 3 dB loss factor is
suggested to compensate for system aging over 20 years.
EXAMPLE:
FOC is 62.5/125 µm multi-mode (DYMEC supplied)
100 kpsi rated 3 dB/km and 3 dB for aging
No other attenuating items in the circuit
initial: 19.5 dB Optical Budget
less: 3 dB aging
less: 0 dB for other circuit attenuation fittings
equals:
16.5 dB
div
ided by: 3 dB/km
equals: 5.5 km maximum distance of FOC between
transmitter and receiver
NOTE
FOC extends communication beyond normal RS-232 or TTL Standards limits. The distance
allowable between Link/Repeaters must be calculated using the factors listed above.
3.2.2 Extending the Distance
Should the distance between two devices exceed that calculated above, it is possible to
insert a Model 5843HRT or Model 5844HRT Link/Repeater to function as a stand alone
repeater, not connected to an IED. Two Link/Repeaters would be necessary, one for each
fiber path. When installed as a repeater only, the 9 Pin D-connector of either Model
5843HRT or Model 5844HRT should be installed with a terminator that covers the pins and
connects the transmit pin (2 or 3 - depending on the DTE/DCE switch position) to the signal
common pin 5 and also connects the signal common pin 5 to the chassis ground pin 1.
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