Moxa ICF-1280I-M-ST [13/16] Fiber signal intensity diagnosis

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ATTENTION

This is

a Class 1 laser/LED product. Do not stare into the laser

beam.

Fiber Signal Intensity Diagnosis

In some circumstances you may need to measure the

receive level of fiber optic channels P1 and P2 with a

voltmeter, which can be connected while the device is

operating (doing so will not affect data transmission).

The measurement can be taken with a voltmeter and

read on a PLC that uses floating high impedance analog

inputs, which allows you to do the following:

• The incoming optical power can be recorded for later measurement

(e.g., to indicate aging or damage).

• Carry out a good/bad test (limit value).

You must use a high-resistance, ungrounded voltmeter to conduct the

measurements, but whatever you do, don’t connect the ground connector

to the housing, since doing so could affect data transmission. In addition,

the measuring cables must be less than 3 meters in length to meet EMC

requirements. Refer to the diagrams below to estimate the quality of the

bus traffic based on the receiving levels.

NOTE

For a valid measurement, the partner ICF-1280I at the other end

of the fiber

optic cable must send normal PROFIBUS frames. This

can be recognized by the LED display of the partner ICF.

A number of different factors can affect the output voltages at the

measurement sockets:

• The partner ICF-1280I’s optical transmit power

• The optical transmitter and receiver’s ambient temperature

• The transmission line attenuation

• The transmission rate that’s in use

Keep in mind that these measurement sockets are not meant to replace a

proper calibrated level measuring device that has a calibrated light source.

The values obtained from the measurement sockets can only be used to

classify the received optical signals into one of 4 categories:

• Good (normal operation, green), 3 V > U > 480 mV

• Critical (optical link margin reduced, yellow), 330 mV ≤ U ≤ 480 mV

• Bad (functionality not guaranteed, red), U < 330 mV

• Fiber cable unplugged, U < 160 mV