User's Manual

Models CH45
EIA 422 or 485
3-2
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-DynaStar, 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-DynaStar, 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-DynaStar 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-DynaStar supplied)
100 kpsi rated 3 dB/km and 3 dB for aging
No other attenuating items in the circuit
initial: 19 dB Optical Budget
less: 3 dB aging
less: 0 dB for other circuit attenuation fittings
equals: 16 dB
divided by: 3 dB/km
equals: ~5 km maximum distance of FOC between transmitter
and receiver
NOTE
FOC extends communication beyond normal EIA 422 or 485 Standard 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
pair of Model CH45 or Model 5843 Link/Repeaters to function as stand alone repeaters, powered
but not connected to an IED. Two Link/Repeaters are necessary, one for each fiber path. The
Repeat Jumpers of each unit is placed in the “ON” position. Serving as a repeater only, the 9 pin
D connector should have a protective cover over the pins.
3.3 NUMBER OF REPEATS
In a loop configuration, the number of units that can be used as repeaters must be determined. A repeater
is any unit that uses the repeat function of the Link/Repeater. All Slaves in a Master/Slave loop are
considered repeaters. Three factors must be considered in calculating the maximum number of repeaters
possible in a loop; the data rate (bits per second), the minimum required width of the original pulse echoed
back to the Master, and the peak operating temperature.