PF14O Error Analyzer

Introduction: 

This guide is to help users of the test instrument to become familiar with the switches, settings, controls and outputs without the tedious reference to the handbook. However this guide is only a brief summary and for further detail the reader will have to go to the handbook. It is included as much as possible the explanations of any abbreviations used so that unfamiliar terms are clear. This will make this guide suitable for students of digital transmission. In association with this and other activities have compiled a dictionary of abbreviations and will be included.

About the Instrument:

The equipment is of German origin and is recognized as one of the best quality. The PF14O is a test set designed for use with Plesiochronous Digital Hierarchy (PDH) and Synchronous Digital Hierarchy (SDH - also originally known as SONET-Synchronized Optical Network). The carry handle is extendable and the lid can be clipped back on to the set in 3 ways, 2 of which during use. The help key, one of the 6: hard’ keys under the screen does not function. You are simply told to see manual’. There are 6 soft keys: F1~F6 beside the screen on the right which change their function according to what is displayed on the screen.

Switching on:

Sit the instrument upright with the screen toward you and the power cord at the top. Switch on using the small black switch at the top right near the power cord. “0” = off. There is a brief self-test and the instrument displays the settings used when the set was last turned off. Re-initialization can be performed by holding down the ‘clear’ key when switching on - but this resets the date and time to zero (1-1-94) and is better left alone unless there is a fault. 

Transmitting:

The set can generate signals from an internal clock (at PDH rates) or from an external clock source (for SDH) and transmit these in a range of selectable line codes (Coded Mark Inversion - CMI, Non Return to Zero -NRZ, High Density Bipolar 3 zeros - HDB3, Alternate Mark Inversion - AMI, and B3ZS).

Receiving:

The set can receive a wide variety of signals and decode them. In ‘framed’ signals the Frame Alignment Word is decoded and checked for errors and information, and the traffic can be demodulated’. The Auto conf (auto configure) key enables the receiver to work out for itself the speed and type of incoming signal.

Functional Test Program. 

Built into the set is a test program that the operator can use just to check that the set is working properly. It requires that two cords are used to connect jack 40 to jack 50 and also jack 42 to jack 53. By reading the printing on the panel layout it can be seen that this simply connects the output of the transmitter to the input of the receiver and also the clock output to the clock input. Start the test by pressing the Test/conf key just below the screen next to the numbers keypad. Then press F5 for ‘self test’. The screen changes to the self test screen and the function keys at the right of the screen allow the user some options - All tests, a single test, a range of tests, show all, Start test, and continue test Press Fl for ‘All’ and then F5 ‘start test’. The printer will give a result, and shown below is the sample for ‘no faults found.

“Paper feed” is the Stop/paper key. The user can experiment by disconnecting the input to output leads jacks 40 to 50 and see the resultant fault’ [fails test 21]. It is not often easy to determine when a test has finished, or if the set has stopped at a failed test. If the set has stopped at a ‘failed’ test, press F6 ‘continue test to continue with the remainder of the tests. The failed test number is printed on the printout.

To get out of any menu back to the one before it, or to simply get back to the start menu on the screen, press the esc (escape) key on the right, below the 6 function keys.

The user may want to change some of the basic setup of the screen (light or dark) or date and time, and this can be done from the test/conf key menu.

Applications

An ‘application’ is simply using the set for a test. Currently there are only two ‘applications’ available: Line Test and Monitor test. A line test is where a pattern is generated and transmitted through the equipment under test and then received and errors counted. A monitor test is where no signals are transmitted but the existing signals of a working system are checked for errors and information.

Setting up to perform a test

Press ‘appl’ key to bring up the ‘applications’ menu. It doesn’t matter where you are in the menus, the applications menu will be presented whenever the key is pressed. Select either ‘Line Test’ or ‘Monitor’ by using Fl or F3.

In order to ensure that the set is working, it is a good idea to connect a test cord from the transmitter to the receiver and make sure that signals are getting through. The ‘no signal’ LED at the left side under the screen should go out and the green LED ‘signal OK’ should come on. By pressing main menu and then Fl Tx (transmitter) setting, then moving the cursor down to the “Error insert” line which is usually ‘off, the operator can select ‘on’ by pressing F2 and then errors are injected at the rate chosen (eg 10^-3) or the operator can inject errors one at a time by pressing F4. When errors are inserted, a warning buzzer is heard and the display alters to indicate the number and other data such as percent (%) Error seconds (ES). Ensure that G.821 results are printed out by pressing F4 “measurement” from the main menu, then cursor down using the down arrow to “Analysis”, then press F2 for G.821. This will cause the printer to print out ES, SES, DM etc. This exercise should be performed by those new to the instrument and at many times during tests to ensure that the signal being examined is the signal required. The same technique is often used to test equipment. If 5 errors are injected then only 5 errors should be received.

FUSION SPLICE LOSS MEASUREMENT

CAUTIONS

v      Do not discharge the splicer if the electrodes are not installed.

v      Use only alcohol to clean the objective lenses, mirrors, and switches and cover panels. Any other chemical may be flame and cause discoloration.

v      Keep the splicer free from sand or dust. Never clean the V-grooves with hard material or rough object. Doing so will damage the surface and degrade the performance.

v      Always replace the electrodes as a pair.

v      Practice adjustment and alignments have been made to all parts of this splicer by factory personnel. Do not loosen any screw or make any modifications to the splicer other than electrode replacements and fuse replacements.

v      Use the carrying case to transport and store the splicer. The carrying case will prevent damage and provide protection from moisture, vibration and shock during storage and transportation.

v      Do not store in an area where extreme heat and humidity are present.

v      This splicer requires no lubrication. Doing so will degrade the performance and damage equipment.

CLEAVING

ROUTINE FIBER CLEAVING USING FK11

Prepare each fiber for cleaving by stripping all coating materials over a length of 4.5 to 5 cm, then 

cleaning the exposed fiber using a suitable solvent. A good “wetting” with the solvent also helps to

reduce static on the fiber. Allow the fiber to dry fully before attempting to cleave the fiber.

N.B. ABSOLUTE CLEANLINESS IS VITAL TO GOOD CLEAVES. FAILURE TO CLEAN CAN CAUSE BLADE DAMAGE.

Set all levers to the up position. With the levers in these positions, the clamps are open; the blade is back in the START position and the tension clamp to the READY position.

Place the prepared fiber into the grooves (insert fiber from the left side of cleaver). Make sure the clean fiber sits well down in both grooves. NOTE: The scale on the left hand clamp is to assist in cleaving at a specified distance from the end of the primary coating. It indicates distance from the diamond blade in millimeters.
Lower the right hand clamp lever (2) to the CLOSED position. Now lower the left hand clamp lever (1) fully to LOCKED position, then clamping the fiber. The right hand clamp lever should now be pressed fully down to the locked position, clamping the free end of the fiber.
Move the lever labeled “3” smoothly downward to the TENSION ON position.

Move the lever labeled “4” smoothly down to release the blade mechanism and cleave the fiber. The green LED will glow for approximately 3 seconds (this is to indicate that the blade is oscillating and the battery is in good condition).

  

Raise level “4 “ to the LOCKED position, open the left hand clamp and remove the cleaved fiber. Return all levers to their START position (up), ready for the next cleave. Remove off cut and store it safely.

FK-11 Cleaver.

ADJUSTMENTS
Tension:
The Tensioner is used to apply tension to the fiber before it is cleaved. Normal setting of this tensioner is 210 of for 125 um fibers (larger fibers may require more tension). To change the setting, raise the lever “C” to the TENSION OFF position (up), now turn adjuster screw “X” 

(accessible through the hole in the bottom of the case) using 2 mm screwdriver clock wise to increase the tension and vice versa.

 NOTE: If correct tension is not known it is best to start with a high tension to ensure cleave and then gradually reduce it until a satisfactory cleave is obtained. This will avoid blade damage caused by failure to cleave.

Blade adjustment:

The diamond blade may become worn after many cleaves, in this case it should be raised to a new position. Proceed as follows: using a 2 mm wrench turn the adjuster screw “Y” (accessible through the hole in the rear of the case) clock wise quarter of a turn. The blade cannot be lowered.

 

SPLICING
GENERAL
Outline of FSM-20CSII Optical Fiber Fusion Splicer

The FSM-20CSII Arc Fusion Splicer is used for splicing SM (Single Mode) optical fiber and MM (Multi Mode) optical fiber.

Mutual aligning of both SM and MM optical fibers is performed automatically by image processing microcomputer built into the splicer.
The power source applicable for this system is AC85 – 265V (50/60Hz) or DC10-15V. The AC voltage selection is automatic.

NEVER USE a cleaning spray on the machine. Spray that includes FREON gas causes abnormally strong discharges. This reduces the life time of the electrodes and may cause damage to the mirrors and lens.

OPERATION

Keyboard Panel

This section gives the key functions of the FSM-20CSII. Fig shows the key layout on the top panel of the splicer. Table shows their respective functions.

No	Name	Function
1	RESET Key	When the RESET which is pressed, the system stops in any step of operation and the fibers move back to Z axis home position. The splice accepts the RESET with a beeping sound and displays “READY” is displayed on the monitor.
2	SET Key	This is used to initiate the gap setting of two fiber end faces and automatic alignment of the fibers. The instructions “GAP SET “ “FIBER OK” and “ALIGNING” are displayed on the monitor at each stage.
3	MODE Key	The FSM-20CSII can be preset to 20 different modes for various fibers SM1~SM10, MM1~MM10). This key is used to select the mode. In SM mode, core axis alignment is performed automatically and in the MM mode, fiber axis alignment is performed manually.
4	X/Y Key	This is used for the automatic field change operation. When the X/Y key is pressed, the fiber image is changed from (X) to (Y) or (Y) to (X). If this is done after a gap set operation, the fibers are adjusted to the center of the monitor and focused automatically.
5	ARC Key	This is used to perform an arc but it will not function while the system is in its automatic splicing operation. No fiber stuffing occurs if this key is operated from the “READY” state or if an arc has already occurred. “**ARC**” is displayed on the monitor just before the discharge is produced. If gap setting has been done, loss estimation automatically follows the discharge operation. This function may be used to re-arc a splice after the automatic process has finished.
6	CND Key	This is used to select the menu options.
7	MOTOR Key	This is used for controlling the splicer motors manually.
8	(up) Key (down) Key	These are used for moving the ‘*’ cursor wherever applicable in the menus and options. When manual motor control is selected, these keys act as “backward” and “Forward” direction controls.
9	ENT Key	This is used to select a menu option for discharge conditions or select a motor control.
10	HEAT Key	This is used to start the heater process. The heat indicator lamp lights during heating.
11	Condition/ Comment Input keys.	These are used for input of the operating parameters or the comments.

Selecting Splice Mode.
Confirm “READY” is displayed on the monitor and select SM mode.
Setting Optical Fiber

1.         Strip, clean and cleave the optical fibers.

2.         Open the wind protector.

3.         Lift the fiber clamps and the sheath clamps.

4.         Place the optical fiber in the V-grooves.

5.         Carefully close the sheath clamp until it clicks. Check that the bare fiber is seated at the bottom of the V-groove. Ensure the fiber end face is positioned between the V-groove and the discharge electrodes.

6.         Repeat for the other fiber.

7.         Carefully close the fiber clamps and then the wind protector.

8.         Press the “SET” key.

The mirror is set, “GAP SET” is displayed and the optical fibers move forward to their initial gap.

 If the CLEANING ARC function is ON, a short discharge now occurs to remove dust from the fiber surface. Press “RESET” and prepare the fibers again if any dust remains after cleaning.

 If the CLEAVE ANGLE function is ON, the end face angles are checked and an error occurs if either is more than 5 or 3 degrees.

Now, the splicer either continues with the splice procedure, or, if the PAUSE function is ON, it stops to allow operator inspection of the fiber images. “FIBER OK” is displayed and a beep is sounded. Press “SET” to continue the splice procedure.

   

Practical Attenuation Measurement

Attenuation measurement is carried out on the installed cable section by means of a stabilized light source and a power meter. Transmission is measured in both directions, at both 1310 and 1550nm. 
The connectors must be cleaned thoroughly before connecting the fibers and taking readings, since a dirty connector can affect the reading significantly

To prevent the light sources connector from becoming worn out, a dual connector patch cord should be connected to the output of the light source the other end of the patch cord should be provided with a bushing. The patch cord must remain connected to the light source for the entire period for measurement( removing it might change the coupling loss readings). Before measurement, the light source and the laser diode module should be turned on for at least 10 minutes (heating time) to ensure a stable light flow. Measurements should be carried out with un-modulated (CW) light.

 The light source is placed at the cables termination point, depending on the direction in which measurement is to be made. A reference value is then obtained from among five separate measurements i.e. after connection and disconnection of the bushing.

The connection of a stabilized light source and power meter for determining the reference value.

The second lowest reading is selected as the reference value. For example, if the following readings were obtained : -1.82,-2.10,-1.85,-1.92 and –1.88 dBm, -1.85 would be selected as the reference value.

The power meter is then shifted to the other end of the cable installation and each fiber is connected to the transmitter and receiver. Five readings are again taken

 When all readings have been taken the attenuation value for each fiber can be calculated. Only the second lowest reading is used in this calculation. For example, if the following readings , -10.56, -10.45, -10.49, -10.66 and –10.37 dBm, were obtained, the value for the calculation would be –10.45 dBm. The total attenuation in the fiber is obtained by substracting this value from the reference value.

Example:     (-1.85 – (-10.45) = 8.6 dB.

 Setup for measurement the cable attenuation of an operational installation.

Power meter and sensor

Power meters and sensors are used to measure the output power of the incident light from both the light source and the installed fibers.

 The power meter normally has built in calibration for the most frequently used wavelengths, but can be calibrated for other wavelengths as well.

 On older types of power meters and sensors it may be necessary to recalculate the reading if output power is measured at wavelengths other than 1310 mm.

 Different types of sensor (optical receiver) are available depending on the type of measurement to be made and the wavelength range. The sensors normally used permit a measurement range from + 10 to –80 dBm. Sensors are normally calibrated for 1310 and 1550 nm. If several power meters and sensors are used simultaneously, they must be calibrated against each other in order to produce congruent results.

 During routine maintenance testing of telecom network installations and for testing relatively small installations, such as data networks, a simple form of power meter should suffice. These handheld instruments have a limited range and not the same reliability as those described above.

 Handheld power meters can normally be connected for testing at different wavelengths: 850, 1310, and 15500.

Stabilized light source (laser diode module)

A stabilized laser light source is used together with an optical power meter to measure the composite attenuation of an installation i.e. from connector to connector. The light source comprises a laser diode module, an automatic power control circuit (APC), a thermo-control circuit and an oscillator (see Figure).

 The light from the laser module is sent into the fiber via a system of lenses. Light from the rear face of the laser diode is monitored and the value fed back via the APC. This gives a constant output power during measurement. The temperature of the laser is monitored and controlled by a Peltier element and the thermo control circuit, which means that frequency variations are counteracted. Intensity modulation is achieved by means of a built in oscillator. It should be noted that all light sources require a heating time of around 10 minutes before the laser reaches its operating temperature and a stable output power is obtained.

 

Block diagram of a stabilized light source with laser diode module

The light sources used today allow both internal and external modulation of the emitted light. Continuous wave (CW) light should always be used for measurement of composite attenuation in installations.

The light from a stabilized light source is continuous (upper graph) while light from OTDR is Pulsed (lower graph)

 

4***Fault tracing.(OTDR)

OTDRs are used for fault tracing. Before measurement is begun, it should be checked that the transmitter and receiver have been disconnected from the fiber to be measured. This is necessary to avoid potential damage to the OTDR and to the transmitter or receiver.

 Network maps, splice plans and possibly overview diagrams are required to facilitate fault tracing. Measurements- primarily on fibers that have caused an alarm or fault registration are normally made in two stages: first approximate localization and then more accurate pinpointing of the fault.

 Approximate Localization.

The OTDR should be set up to show the entire cable length on the screen. The pulse duration normally used is 2 or 4 us.

 If the fiber is broken, the curve will show considerable reflection (end pulse) in the installed fiber and if there is greatly increased attenuation at an isolated point in the fiber, this will show as a sharp knee on the curve. Such points should then be expanded to provide better reading resolution. The approximate position of the fault is also determined.

 It should be noted that the fiber break is located in a cable section between two splices, the thixotropic jelly filling in the cable will reduce the end pulse.

Pinpointing the fault.

For the final pinpointing of the fault ©,  as short a pulse as possible should be used and the graph should  be expanded maximally around the area where the fault is suspected. After averaging, the distance to the fault is determined.

To determined the position of the fault more exactly, a known point in the cable such as a certain splice may be chosen as a reference point. The distance to the fault is measured with the OTDR set to reference measurement. In this way, the distance from the known point to the fault will be obtained.

Measurements are mode from both end points to check that the sum of the distances from A to C and from B to C is equal to the length of the fault cable.

 The distance to the known point is determined with the help of network maps and splice plans. The refractive index of the instrument should be adjusted so that the distance shown on the instrument is the same as the actual physical cladding length. The position of the fault is then measured with the adjusted refractive index value.

 

The five point method

Measurements are made at five points on the graph in such a way that two of the points are before the splice, two beyond, and the fifth in front of and close to the splice.

A line Y1=a1x+b1 is drawn through the first two points before the splice and a second line Y2=a2x+b2 is drawn through the points beyond the splice.

The splice loss at x, is thus :

                        A (x2)=y1=y2=x3(a1-a2)+(b1-b2)

The calculation shown above is done by a microprocessor-based program and the value of the equation is displayed on video screen.