IEC 61280-2-4:1998 pdf download.Fibre optic communication subsystem basic test procedures – Part 2-4: Test procedures for digital systems – Bit-rate tolerance measurement
1
Scope and object
The object of this test procedure is to measure the bit-rate tolerance of the fibre optic digital
subsystem under specified conditions.
Bit-rate tolerance is defined by the clock frequency range of the fibre optic digital subsystem
which meets the specified bit error ratio.
2 Apparatus
2.1BER test set (pulse pattern generator, error detector and frequency synthesizer)
The test set shall be capable of providing a pseudo random bit sequence to the system
consistent with the signal format (pulse shape, amplitude, etc.) required at the system input
electrical interface of the transmitter device.
2.2 Optical power meter
The optical power meter, which has a resolution of at least 0,1 dB, and which has been
calibrated for the wavelength of operation for the equipment to be tested, shall be used.
2.3 Optical attenuator
The attenuator shall be capable of attenuation in steps less than or equal to 0,1 dB and should
be able to provide total attenuation 5 dB to 1 0 dB more than the system gain. Care should be
taken to avoid back reflection into the transmitter.
2.4 Jumper cable
Unless otherwise specified, the test jumpers shall have physical and optical properties normally
equal to those of the cable plant with which the equipment is intended to operate. The jumpers
shall be 2 m to 5 m long, and shall contain fibres with coatings which remove cladding light.
Appropriate connectors shall be used. Single mode jumpers shall be deployed with 90 mm
diameter loops. If the equipment is intended for multimode operation and the intended cable
plant is unknown the fibre size shall be 62,5/1 25m.
2.5 Test transmitter
The test transmitter shall have electrical, optical, and mechanical characteristics similar to
those of nominal transmitters that are used in the specified fibre optic terminal device.
3 Test sample
The test sample shall be a specified fibre optic receiver. The system inputs and outputs shall
be those normally seen by the user of the system. The test receiver shall be installed in the
measurement configuration as shown in figure 1 .
4 Test procedure
4.1 Unless otherwise specified, standard operating conditions apply. The ambient or
reference point temperature and humidity shall be specified.
4.2 Apply appropriate terminal input voltage to the system under test. Follow appropriate
standard (or extended) operating conditions. Allow sufficient time (30 min unless otherwise
specified by the manufacturer) for the terminal under test to reach steady-state temperature
and performance condition.
4.3 Turn the measurement equipment on and allow the recommended warm-up and setting
time to achieve the rated measurement performance.
4.4 As part of standard operating conditions, all the terminal inputs shall be fully loaded with
the pseudo random data (maximum possible word length: typically 2 +23 – 1 ). Select a channel
to be monitored. Connect the terminal output of the receiver portion on the BER test set.
4.5 Adjust the bit rate of the pulse signal to the nominal value.
4.6 Connect the reference jumper cable from the output of the variable optical attenuator to
the optical power meter.
4.7 Adjust the optical attenuator to set the received power at the manufacturer specified
minimum received power level.
4.8 The jumper cable shall be reconnected to the input connector of the receiver.
Measure the bit error ratio.
4.9 Repeating step 4.9 change the pulse repetition frequency. The bit error ratio versus the
bit rate shall be measured by an applicable step Plot BER versus bit-rate (B) using a graph
sheet similar to that in figure 2. Unless otherwise specified, b shall be 1 0 ppm of the nominal
bit-rate.
IEC 61280-2-4:1998 pdf download
