How to Use PC/Laptop for Loopback

How to Use PC/Laptop for Loopback

Loopback-A very old and fool proof trick in books is loopback as we discussed earlier in posts about protocol.

RS-232 and RS-422 are full duplex protocol so data and be send and receive a the same moment,
So if i can short Tx and Rx lines at any receiving end i should get back what i am sending.

This test i can use Main pilot computer in control van in which telemetry software is loaded or your personal laptop or work pc.

Personal laptop or work pc are used in case you want to check the continuity of the circuit in case pilot computer is not a part of circuit for example-Sonar running on Fiber optics is completely isolated from pilot pc so to check this circuit we need to do this test via PC.

As your PC also sends out RS-232 via USB ports or if you are lucky you will have Desktop with DB-9  connector and if not you need USB to Serial port convertor(DB-9).You can either buy it from any electronics hardware store or make one yourself if you are offshore, Just search on google how to do it.

Click on Start->All Programs -> Accessories -> Communications -> Hyper Terminal

Now when you will click on hyper terminal it will ask you to make telenet a default program for your computer,Select NO and then a box will appear asking for country code and number-click on Cancel.

Then finally a box will appear(As shown below) asking for connection name,Fill in XYZ whatever you like and click OK.

Then a new Box will appear as shown below and instead of TCP/IP select port 1from connect using Drop down menu.

Once you click ok another box will appear asking for PORT settings,In these settings the first one is selection of speed or Bits per second,You can choose according to your system Modern ROV's like SMD or Even old sea eye's mostly use speed of 115200bps,Select from the drop down menu which suits you the most.

Another parameter is Flow control at bottom,Select None from drop down menu and that's it no other option we need to change.

We are ready for test our sonar circuit.

Click OK and a new blank notepad type window will appear,Start typing any rubbish, Until and unless you short Transmit and Receive line you will not see anything on screen because in hyperterminal you can only see what you are receiving but you cannot see what you are sending.

When you will create a short between Tx and Rx on sonar plug,If your circuit is fine till that point you will should see what you are receiving and if its a open circuit in between you will have a blank screen.

You can apply this technique on any equipment as your PC serial port also gives out RS-232,Which is a full duplex protocol.

I hope this info will be useful in troubleshooting

Regards

Deepanshu Giri

Pin Configuration of Wago Connectors

Pin Configuration of Wago connectors

As requested by some viewers here is the pin description of Wago. 

Pins	RS-422	RS-232	TTL	RS-485
Pin 1  Pin 2  Pin 3  Pin 4	A  +Rx  B   -Rx  Y   +Tx  Z    -Tx	GND  Rx  Tx  N/C	Input  N/C  Output  GND	+Tx/+Rx  -Tx/-Rx   N/C   N/C

Troubleshoot tricks for Focal 903

Troubleshoot Focal 903

I recommend before you start reading this post please read the post about basic Information of Focal 903.

I will first start with surface unit as this unit is easily accessible to techs and discuss various LED's and indicator and their use while troubleshooting.


Fuse-There is a 1 Amp fuse at the back of this unit and if you are running on fluctuating power supply this is the only protection this unit has so if this unit is not turning on,Please check this fuse.

Power Supply Indicator-The Power supply module has 3 LED's on it which displays three out put voltages of power supply,As this unit comes with different types of power supply depending on model and requirement but most commonly used one is the one with 240 V input supply and output of +12v,-12v,+5v and you can check the output by looking at the glowing led's.

Note-Power supply for focal unit can be operated on 120v or 240v,Some power supply models comes with auto selector function while some power supply has manual switch in it to select the voltage and to access this switch you need to open power supply cover.

Tx and Rx LED's on data channel-This is my favorite as from this you can tell which side of focal 903 has problem.

When telemetry is working fine both RED and GREEN led's will blink continuously telling you that focal is receiving and transmitting data.

In surface focal unit RED led represents local computer and Green led represents remote computer(POD),So if your green led is blinking and red is not,This condition represents that pod is sending data but computer in control van has problem.

This logic applies for both surface and Subsea unit as for subsea unit POD will become local computer and control van computer will become remote computer and logic will remain the same

RED LOCAL -GREEN REMOTE

So just by looking at these led's a technician can tell which part has problem surface or subsea.

Note-These LED's should be blinking and not solid on, As blinking led represents data transfer and some systems have high data rate and led blinks at such a fast rate that led appears to be solid, so watch it carefully.

LINK LED-Link LED represents that focal unit is receiving enough optical power from other end and fiber is GOOD but this does not represents that telemetry is working.

Diagnostic Port-There is a separate post about using focal 903 diagnostic port,Please refer to that post.

Video Signal-when focal receives a video signal led related to that particular channel will blink and indicates video signal is being received.

How to test daughter card on AIB backplane-Take a Fluke multimeter(Only fluke) and select diode mode place black lead on the bottom most pin and red lead on the second pin (Last two pins) and red led will glow and indicates daughter card is working fine.


Note-This is only applicable  for RS-232 data card.

If daughter card has gone bad you need to replace it,Please make sure you take precautions while handling cards as daughter boards are sensitive towards electrostatic interference.

Note-when replacing daughter card on AIB module please align the white dot on card as well as on backplane as daughter card can be fitted both ways.

Now Lets talk about Subsea unit

Subsea unit has a 3Amp fuse on back plane and when this fuse blows and you don't have spare one no need to worry,Open backplane and there will be another fuse fitted as SPARE fuse.

Link LED and Video led's have same function as on top unit.the only difference you will find that the subsea unit is a high density unit,Hence smaller in size.

How to Use Power Meter

Power Meter

Another measuring instrument for fiber optics and much easier to use as compare to OTDR but will not give you much details as OTDR.

So Power meter box comes with 3 major components-
1) Light Source
2) Power meter
3) Fiber of small length-Calibration cable

Most of the light source can transmit laser at 850nm,1310nm and 1550nm and depending on your system you can choose the wavelength required.

I will choose 1550nm because all the systems i worked on has Focal 903 and downlink wavelength in focal 903 is 1550nm.
Once you have selected wavelength in light source choose the same wavelength in power meter as well.

Take calibration cable and fix between light source and power meter,Switch ON both devices and note the reading in dB,I prefer it in dB because its easier for me to calculate but you can do it in dBm as well but make sure to do calculations accordingly.

Note-Techs taking reading in dBm will get readings between -2dBm  to -8dBm

You must see reading of about 65dB-75dB and if battery of any device is low you might get an error reading so be aware of this.
Note down the reading as this is our benchmark lets suppose 70dB(Benchmark reading) in this case.
Now Connect Light source at starting point in this case i am measuring total system loss by connecting light source at start of fiber in control van by disconnecting fiber at surface FO
and Power meter at the subsea end as this for illustration purpose only you can even place a particular junction box in between.

**Important Note-Do not disconnect calibration cable from the circuit while performing test

Now the reading in power meter will be suppose 60dB(Final Reading)

Total Loss in a System= Benchmark Reading - Final reading

                         10dB  =70dB - 60dB

So in this case we have loss of 10dB in whole system from Surface to subsea.
You can use this method for a particular connector as well, by placing a connector in between instead of whole system.

I hope i have explained it well on how to use power meter but if you still have any question please use the comment section.Next post i will explain how to troubleshoot FO 903

Welcome to My Blog

Hello All,


Welcome to my blog as i have just started this blog yesterday(06/06/2012) only and able to do 4-5 topics only.


I will keep posting something new everyday as i have lot to share regarding ROV's as this keeps me busy when i am not working offshore.


If anyone needs information on a particular topic or wants to contribute to this blog,You are more than welcome.


I am always ready to learn something new regarding ROV's.


Keep visiting the blog or subscribe for updates.


Thanks and Regards
Deepanshu Giri

Loss in a Fiber System

Loss in a Fiber System

So its a big question when taking measurements what loss i should see when measuring a loss in a connector or a Fiber optic slipring below are some ballpark figures which will help you out in a field.

Fiber cable- 0.4dB/Km - 0.7dB/Km

Slip-Ring/FORJ - As depending on which channel of fiber optic slip ring you are using loss will be considered if we consider a 5 channel slipping and loss will be minimum in channel no-1 and maximum loss will be in channel no 5.

Channel no # 1 - 2 dB
Channel no # 2 - 2.5 dB
Channel no # 3 - 3 dB
Channel no # 4 - 3.5 dB
Channel no # 5 - 4 dB

Connector -0.25 dB

Barrel or Union Connector- 0.5 dB-1 dB

I have calculated on papers with 4km of umbilical and 600 mt of tether taking in consideration all connectors, The maximum and minimum loss in a system should be

ROV                                                                              
Maximum Loss-16dB
Minimum Loss-11dB

CAGE/TMS
Maximum Loss -12dB
Minimum Loss - 7 dB

You have all the figures you can calculate on your own by taking all the connectors in consideration.

Diagnostic port of Focal 903

Diagnostic Port of Focal 903

 Focal 903 is very robust fiber optic unit and with the facility to remotely monitor temperature and DB loss in fibers of subsea unit with the help of Diagnostic port.

So while sitting in control Van we know temperature of both units and Db loss in our fibers.

We can record a log when telemetry is good and compare during troubleshooting like fiber loss and temperature of units.

Procedure to Use Diagnostic port.

DB9 female connector on console unit is the diagnostic port of focal 903.

Prepare a short whip between your PC to Focal connector, It will be straight connection

Install  Focal software (Which comes in Focal Disk )on your laptop or PC."This Software cannot be installed without internet connection"

Switch on Focal 903

Click on VDM icon on desktop. If you can’t see VDM icon on desktop please go to C drive -Program files-VDM (Folder)-VDM icon.

Once you click on icon it will start monitoring all parameters like Db loss in fiber and uplink loss/downlink loss. and temperature of both subsea and console unit.

So if we make a log of parameters during normal condition’s it will be easy when we have to troubleshoot system.

The readings which you see regarding loss in uplink and downlink will not be accurate until and unless to calibrate your software,You need to take dBm readings from both transmitter and receiver and enter it manually in software by clicking on calibrate,After this only loss readings will be accurate.

FOCAL 903 Basics

FOCAL 903 Basics

Before i teach you troubleshooting its important to learn some basics about this wonderful unit.

SO there are two units Surface and Subsea at first i will talk about surface unit only and later on about subsea unit.

High Speed and Medium Speed unit 

There are two types of surface units available one is High speed and another is Medium speed unit,The only difference between the two is number of data and Video channels available in a unit.

As Shown in figure is a medium speed unit and has 8 data channels and 4 video channels while the high speed unit has 16 data channels and 8 video channels,Mostly in Vehicle is a high speed unit and for cage or TMS is a medium speed unit due to less number of camera's and equipments.

Now in Medium speed unit there are 2 backplanes also known as AIB (Adaptable interface board) 1 AIB has 4 data channels slots to place daughter cards in it, One backplane is dedicated to RS-232 and cannot be configured for any other protocol.So we have 4 RS-232 data channels

The second backplane also has daughter card slots,User can place any daughter card according to requirement e.g. RS422/485, Arcnet or even RS-232.

While in High speed unit there are 4 backplanes out of which 2 backplanes are dedicated for RS-232 and other 2 backplanes can be configured for any other protocol according to requirement.Please refer to fig below to see which backplanes are dedicated for RS-232.

Now we have learned some basics about Surface unit let's talk about subsea,Subsea units are also referred as HD (High Density) units as well because of shortage of space subsea units are compact and smaller in size so they can be fit in POD.The difference of High and medium speed and allotment of AIB backplanes are same as it was in Surface units.

Operation of FOCAL 903

As One of the biggest advantage of Focal 903 is a backup fiber and Diagnostic port that gives the real time monitoring of Fiber loss,These is a separate post on how to use diagnostic port.

So lets talk about back up fiber as there is a selector switch to select between Fiber 1 or Fiber 2 or leave it on automatic mode and fiber with minimum loss will be selected.(See post Loss in a FO).

Always remember when you do bench test for these units it is recommended to have minimum 5dB of loss between surface and Subsea unit.

The maximum loss between Surface and Subsea Unit can be around 20dB,For more information on losses please refer to blog post Loss in a FO.

In my next post i will write about Troubleshooting Focal 903. 

How to measure loss in each FO connector using OTDR

 How to measure loss in each FO connector using OTDR

Typical losses on fibers:

Per 1Km fiber: 0.4-0.7 dB.

Slipring: 2-5 dB. –channel 1; 2dB max, channel 5; 5dB max.

Barrel (calculated including 2 connectors): 0.5-1 dB

Connector: 0.25 dB.

The Focal units require a minimum loss of 5 dB between units or the units will get destroyed, maximum loss unit to unit is 20 dB, any more than 20.5 dB and the units will not communicate, normal loss for a system is 12-16 dB.

The OTDR requires a “launch cable” of minimum 48 meters length as the unit is not able to read any information in the first 48 meters of fibers.

Attach the fiber launch cable to the top of the unit, attach the launch cable to the system using a barrel connector.

Press the red on/off button to turn unit on.

Unit will start in Standard mode (shown above).

Press Enter.

You will now arrive to the screen shown above.

Press f3 to choose the Wavelength of 1550

Press f4 to choose the length of fiber (always choose slightly longer than your total system length.

Press f5 to choose Display from origin.

Press f6 to jog through to next page.

Press f1 to choose 30 seconds test time.

Press f6 to arrive back to above page.

Press f1 and the unit starts testing the fiber, wait until the yellow icon to the left of the battery icon stops blinking.

Use the wheel on the top right of the unit to move the red scroll bar, click the wheel and a new scroll bar (blue) will appear, move this scroll bar in the same fashion.

The distance from the start point (the OTDR itself) and the first and second scroll bar are shown in the lower left hand corner of the screen, the loss between the scroll bars is shown to the right of the lower left box on the screen.

By moving the scroll bars you can now pinpoint the losses at the various parts of the system.

RS-232,RS-422/485 Troubleshooting Trick and Tips

RS-232,RS-422/485 Troubleshooting  Trick and Tips

Let's Start with RS-232

Protocol

RS-232 is a Full duplex protocol means user can send and receive data at same time. Its a 2 way transmission like mobile Phone but It can travel distance of 50Ft /17mt.

How to Identify Transmit line with the help of Multimeter in RS-232

RS-232 sends signal in form data packets and these data packets contains 0's and 1's like any digital signal.These 0's and 1's has certain voltage level,In this case mostly its around +12v for 0 and -12v for 1.


Now a interesting fact- Whenever RS-232 line is ideal it will sit on logic 1(-12v), And the baud rate or speed  rov use most of the times line is ideal.So we will use this property to identify transmit line.


Place black lead of multimeter to shield and red lead to any of the other two wires, The wire which will show -12V on multimeter is transmit line.

Now -12v is in books in reality anything over -4v is good enough but make sure voltage should not be less than -3v on receiver otherwise data will be corrupted.

Getting –ve voltage does not mean that you are receiving or sending any data, It only tells you that computer is ON to verify that you are actually sending or receiving data, take out O’scope or LED.

Place LED between shield and transmit line if LED blinks that means you are transmitting data but if LED is solid bright it means computer is on but not transmitting. Do the same for Receive line.

In O’scope you can actually see data packets and pulse width by adjusting time scale division on o’scope and now a days in modern o’scope everything is adjusted automatically.


If you are dealing with any kind of signal,Always use Shielded twisted wire pair and never use twisted pair which is made by yourself by twisting 3 wires together as it will not serve the purpose.

RS-422/485

RS-422/485 both of them have same properties except the fact RS-422 is a Full duplex protocol and RS-485 is half duplex,I have already explained full and half duplex in previous post when i discussed protocols,

so RS-422/485 signals are never measured with respect to ground because is a differential signal between transmit(Tx) and receive(Rx) line so we need to measure between tx and rx.

Now what you expect to see is between 2v-4v it doesn't matter that voltage is negative or positive as signal is like a battery depending on where you have placed multimeter leads.

The signal is good above 0.2v as below this voltage level signal will get corrupted.

One more important thing when you are connecting RS-422/485 that never connect ground on both sides of circuits otherwise signal will start flowing through ground,However companies recommend to connect ground wire on one side of circuit but i usually don't connect it all on either side and it works without any problem. 

3 Major Protocols used in ROV

3 Major Protocols used in ROV 

Now a days when most of rov's are fully fiber optic from surface to vehicle but we still need to use some protocols like RS-232,422,485 as computers still work on electrical signals not on Fiber optics.

We will discuss 3 major protocols used widely in ROV's.

RS-232- RS 232 is used to transfer data for short distance up to 50ft/17mts (in books) and up to 80 feet in practical,As this is a full duplex protocol you can send and receive data at same time.

RS-422 - RS 422 is use to transfer data over long distance up to 4000ft/1300mts,This is also a full duplex protocol.

RS-485- RS485 is same as RS-422 only difference is RS-485 is a half duplex protocol as you can either send or receive data,Practically speaking this type of protocol i have used a lot in SMD systems,It has benefit that you only have to use 1 twisted wire pair(twp) for signal as compare to 2 twp in RS-422 or RS-232.

As the distance specified are bookish numbers,You can double the distance if Data/Baud/Bps rate is half so if your telemetry is working at 19200bps you can use RS-232 for longer distance as compare to when your telemetry is at 38400bps. 

Now when you have learned some basics of these protocols it time to learn some tricks related to these protocols follow the next post to learn some fool proof troubleshooting tricks related to these protocols.