• the sensitivity of the receiver on the end device
• the optical power delivered into the cable.
The optical power delivered into a cable by the device’s transmitter is as follows:
Core Structure
50/125 µm POF
62.5/125 µm POF
100/140 µm POF
200 µm HCS
Typical Optical
Power
-15.8 dBm
-12 dBm
-8.5 dBm
-4.5 dBm
Worst Case Optical
Power
-19.8 dBm
-16 dBm
-12.5 dBm
-8.5 dBm
Assuming worst case temperature conditions, and that the fiber cable has a high-quality polished termination, an
upper boundary for the cable length can be calculated using the worst-case optical power from the table above, and:
• the cable’s attenuation figure (check its datasheet)
• the receiver sensitivity (check its datasheet)
Length (km) = (Worst Case Optical Power (dBm) – Receiver Sensitivity (dBm))/(Cable Attenuation Figure (dB/km))
If you were using:
• a 62.5/125 µm POF cable with a high-quality polished termination
• a typical 62.5/125 µm cable attenuation figure of 4 dB/km
• a Microchip Isolated Timing Repeater (ITR) as the end device, which has a receiver sensitivity of -24 dBm
the upper bound for the cable length would be:
Length = ((-16 dBm) – (-24 dBm))/(4 dB/km) = 2 km
In this scenario the cable length shouldn’t significantly exceed 2 km. Ensuring the environmental temperature is
always roughly 25°C allows for more cable length.
A repeater such as the Microchip ITR can be used if cable runs that greatly exceed the length boundary are required.
Connecting a cable into a ST Fiber port:
1.
If present, twist the device’s black plastic cap on the fiber port counterclockwise so it is no longer locked in by
its notches, then gently pull it off the port
2.
Rotate the outer part of the cable’s ST connector so that the outer notch is at 90 degrees to the inner notch
3.
Line up the ST connector so that the port’s inner notch is in in line with the topmost notch on the TX fiber port
4.
If not rack mounted, place one hand on the GridTime 3000 to ensure it doesn’t move
5.
Gently slide the ST port into the TX fiber port until it hits the end
6.
Push the outer part of the ST connector down the tracks and twist it clockwise so it locks in place
7.
Connect the other end of the cable into the relevant port on your end device, follow a similar process to plug in
the connector.
Removing a cable from a ST Fiber port:
Installation
©
2022 Microchip Technology Inc.
and its subsidiaries
Manual
DS00004572A-page 47
