[attachment=1891]
[attachment=1891 Wrote: PJW pid='6019' dateline='1444240443']
(07-10-2015, 09:12 AM)hariram Wrote: (07-10-2015, 06:39 AM)Hi Peter,I am sharing few more information to resolve the confusion between TTU/ETU/TC or TU/ETU/TCU. Wrote: I too have little knowledge of AFTC working. Here i am stuck up with TCU i.e Track Coupling Unit testing.
Attaching file for better understanding.
(07-10-2015, 04:51 AM)hariram Wrote: Hi Peter
Thank you for all information !!!
..........................................................................
Now with the above information I am testing TCU but ideally i have no idea what should be the load,as it is directly connected to Track. Secondly as TCU has single side track its load should be half of TU.
I need more information regarding TCU testing in ideal condition.
Thanks
Hari.
From the picture you helpfully attached, I am a little bit confused and will need to check the literature.....
It does sound as if you are using the equipment in a configuration with which I am not familiar.
You are probably right; in my days the TI21 could only be used as a double rail track circuit.
However I do know that it can now be used through pointwork as a single rail track circuit but do not know what components are required for this; I shall have to bring my knowledge up to date and respond to you later.
But in the meantime, I still don't actually understand precisely your use of the word "load".
I agree that the track circuit would form the electrical load for the transmitter as seen via the various transformers etc. so I have no problem with the term in that context; however I do not comprehend why you would need to know its value when testing the track circuit set up. Please explain further.
I am still trying to digest all this; I think you are giving me rather more info that I am able to give you!
I failed in my quest to have a look at the latest Ebitrack Manuals; unfortunately the company's IT system was having a more than usually bad day and trying to do anything was challenging, so certainly couldn't go browsing in standards. Perhaps tomorrow, IT permitting........
Comments so far in blue below-
3.4 Tuning Unit & End Termination Unit.
3.4.1 Tuning Unit :
.....................For a particular frequency, there is a ratio between the voltage across the tuning unit of that frequency and voltage across its companion tuning unit, the ratios for each frequency and for various Tx/Rx arrangements are given in section 17.1 of Test G.
All this sounds very familiar to me for a typical tuned area with a pair of TTUs.
The low impedance circuits in the Tuning Units (TU) also serve the very important function of shorting the rail-to-rail traction harmonic voltages at the track circuit frequencies. Thus the track circuit frequency component of
the rail-to-rail traction voltage is kept low enough not to swamp the Receiver (Rx) and assist in preventing it
from de-energizing the Relay ® when the track circuit is clear.
Don't think I knew this, but sounds logical.
The Transmitter (Tx) output and the Receiver (Rx) input provide low impedance to the track circuit, which is
essential for correct tuning of the tuned area.
Yes, the low resistance of the entire circuit is essential for the tuned zone achieving a decent rejection ratio.
On the Tuning Unit (TU), the Receiver (Rx) is always connected to the terminals 1 & 2.
For normal power mode (track circuit lengths of greater than 200 m), the transmitter is connected to the terminals 4 and 5, whilst for low power mode (track circuit length of 50 to 200 m), it is connected to terminals 1 & 2.
The overlap zone of the tuned track circuit is measured from the point midway between the Tuning Units (TU).
Within this region both the track circuit may be de-energized by a shunt. The length of the overlap zone
depends on ballast conditions.
All very familiar to me for a tuned zone.
For Broad Gauge (1676 mm) (BG) the length of tuned zone is 19.5 +/- 0.5 m and for Meter Gauge (1000 mm)
(MG) the length of tuned zone is 22 +/- 0.5 m.
I wouldn't have known the measurements but was aware that the gauge of the track would affect; standard gauge in the UK lies between the to Indian gauges and the tuned zone is 20m +/- 0.5m, so this rings true.
3.4.2 End Termination Unit:
...................The end termination unit is a self contained tuned circuit for the electronic separation for track circuit isolation is not required. Such applications are:
(a) end feed, or end receiver, adjacent to insulated rail joints or,
(TCU’s are now being used for such application instead of ETU).
(b) Center feed arrangements.
The End Termination Unit (ETU) employs the same housing as Tuning Unit (TU) and the same terminations.
i.e. output to track on T1 & T2, input from Transmitter (Tx) on 4 & 5 for normal power and 3 is the earth screen.
In low power mode the Transmitter (Tx) will feed in on 1 & 2 or output to Receiver (Rx) from 1 & 2 terminals for both normal and low power applications.
Again, this accords with my memory; the only thing I did not know was the utilisation of TCUs in preference to the ETUs
3.4.3 Specification of TU and ETU:
• Maximum permissible rail to rail voltage : 110 V AC or 160 V DC
• Mounting : Vertical
• Track to Tuning Unit (TU) /End Termination Unit (ETU) cable: 2C-19 x 1.53 sq. mm (35 Sq.mm) copper cable or 50 Sq. mm equivalent aluminum.
• Maximum length of Track to Tuning Unit (TU) / End Termination Unit (ETU) cable:
Long cable 3.95 m ± 0.02 m
Short cable 2.35 m ± 0.02 m
Weight
• Tuning Unit: 8.5 Kg
• End Termination Unit: 9.5 Kg
After all these years I can't recall the length of the track leads (they came pre-made in 2, then 3, pre-set lengths ordered by part number from the stores). I do remember there was a period in the late 1980s when they came with incorrect insubstantial ring lugs and so had to hacksaw them off and re-terminate in the proper lugs using a hydraulic press which we had to import from the USA- but that is another story.
I would never have known their weight.
However this has brought back memories of about 1986. We had a gruesome shift humping a whole lot around at Totnes when we discovered just after a commissioning that we needed to change the design in a hurry. There had been a wrongside interaction between the new TI21 tracks on one track and the pre-existing Aster tracks on the other. Someone in their wisdom had decided to set the standard to use freqs C&D on the Down line (on basis that it was easy to remember) yet it transpired that these TI21s had almost exactly the same nominal frequency as the single tone Asters already fitted to the adjacent Up line; since these were marked in Hz but the TI21s only known by their letter code, the similarity was not immediately obvious until the crosstalk occurred!
We then had to swap all the Up line equipment with all the Down line equipment in a hurry; trains were still being run through the area under handsignalling and of course there was no design, so it was a question of removing units and keeping track of the alternation until found a track which had the type of equipment you wanted for your track in return [in a crisis it was acceptable to work like that in those days and the job was certainly done and finished quicker than we'd have got a single mod sheet- it would have taken about 3 hours to get to site by High Speed Train even after it had left the design office and of course no such thing as availability of fax or email in those days]. The weight certainly seems about right because a pair of TUs was all one could sensibly carry when walking on ballast and even then everyone's arms ached by the end of the day.
Actually we used to have a "short lead" and a "long lead", but that meant the TUs were quite close to the track and we then changed over to using a pair of "long leads" for the shorter and a pair of "extra long" leads for the longer.
Whereas the usual orientation is vertical, we certainly did occasionally have to mount them on their back between the rails in certain places; I do think it was "permitted, but non-preferred" but of course more at risk of damage as well as being less safely accessible to the maintainer.
Using 2.5mm cable imposes a severe (35m) length restriction between Tx and its ETU/TTU. For a time it was permissible to use 10 sq mm cable instead and that permitted a longer length (can't recall, perhaps 100m). However nowadays the solution for Tx ends over 35m is to use an LMU (Line Matching Unit) in the location to boost the voltage at the outgoing links (I think basically a 1:10 step up transformer) and then mount another LMU at the TTU/ETU to step the voltage down again- this means that the cable between is only 2.5 sq mm and the feed can be several hundred metres.
3.5 Track Coupling Unit
3.5.1 Principle:
Schematic diagram for Track Coupling Unit (TCU) is given in Drg. No. IN1D0194. TCU is a passive device. It
can be used to terminate the track circuit. It consists of a capacitor, resistor and a transformer in series. It is
basically a band pass filter tuned at a particular frequency.
The major applications of TCU are as follows:
1. To terminate a track circuit.
2. In the point zone track circuit.
3. In the yards where it is difficult to form the tuned zone.
The advantages of using TCU as compared to ETU are as follows:
1. The main difference between TCU and ETU is that TCU can with stand 400 V DC / 275 V AC r.m.s. as
compared to 160 V DC / 110V AC r.m.s. for the ETU. Hence TCU can be used for Single rail
application.
2. TCU can be kept at a distance of 130 m from the rails. This facilitates the use of TCU in complex yards
where there is space constraint.
3. With TCU it is not necessary to use 35 mm sq. cable for connecting TCU to rail. 2 x 2.5 sq. mm can be
used.
4. Impedance Bonds are not used with TCU but are used with ETU.
These are the things that I know nothing about. Assuming that the office IT is functional tomorrow, I'll try you see if this accords with the single rail Ebitracks in use in the UK.
However I am not sure whether we are actually going to get to the answer of your original question; indeed I still don't quite understand why you are trying to find out the value of the "load" when testing the track.
Is there a "Test Specification" of some sort you are using which you could post?
Otherwise perhaps the other Peter or someone else has access to the material that may help to cast further light on the topic.
