01-02-2010, 08:06 PM
Could someone please explain the operations if a TI track circuit, with regards to TTU's and ETU's.
Many thanks
Many thanks
TI track circuits
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01-02-2010, 08:06 PM
Could someone please explain the operations if a TI track circuit, with regards to TTU's and ETU's.
Many thanks
01-02-2010, 11:16 PM
(01-02-2010, 08:06 PM)Archie Wrote: Could someone please explain the operations if a TI track circuit, with regards to TTU's and ETU's. The TTU and ETU are the trackside units that the rail connections attach to. The TTU carries out the electrical equivalent of the block joint. Obviously the function of the IBJ is to electrically separate the two track sections as far as the track circuits are concerned. To this end, if you understand a bit about transmission line theory and tuned circuits, you will be able to see that with the right component values, you can arrange for it to behave like short circuit shunt for the right frequency. The key is not a single TTU but a pair of them separated by (for UK mainline rail sections on concrete sleepers) 20m of rail. The pairs in the case of TI21 are A and B, C and D, E and F, G and H (advanced users should note that A and E, B and F, D and G, D and F can be used but that is a different topic). The components in the TTUs, together with the complex impedance of the rails and sleepers forms a tuned zone. For two TCs of ,say A and B frequency, when TC current at frequency A encounters the tuned zone, it circulates in there in such a way that the far end of the zone between the rails is effectively a short circuit hence very little of the current at that frequency leaks into the other TC. The reverse is true for the B frequency circulating from the other TC. So, what does and ETU do? I said that a TTU is no use on its own because it needs the additional components of the companion TTU and the rail and sleepers. An ETU for a given frequency effectively has all of the components needed to look enough like a full tuned zone for the TC to work, assuming it is installed with the track leads 1m from the pair of block joints. This means that for TCs in plain line you would see pairs of TTUs and for the last TC of this type before another type of track circuit which needs a block joint, you will have an ETU. There is a useful property to save on equipment if you want to end a track circuited section where TI21s are used and that is that you can avoid the need to fit block joints by using a TTU and fitting a dead short across the rails 18.5m from the TTU. As far as the track circuit is concerned, the characteristics of the tuned zone are identical and in this case, rather than the companion TTU being the short circuit, there is a real one there, but on the TC side of the tuned zone, it appears invisible so you can measure the correct track circuit voltage. As you ask about TTUs and ETUs, I guess you either understand or don't need to know about how / what the transmitter and receiver in the loc does. I hope that gives you some idea of how they work, but please feel free to come back if you have other queries. Peter
02-02-2010, 08:00 AM
(01-02-2010, 11:16 PM)Peter Wrote:(01-02-2010, 08:06 PM)Archie Wrote: Could someone please explain the operations if a TI track circuit, with regards to TTU's and ETU's. I thought I had a model answer to an exam queston on such a subject but can't immediately find it. Hopwever I did find two Powerpoint drawings that I did for it, so I attach these to illustrate Peter's description
PJW
16-02-2010, 01:31 PM
There are some caveats with TIs. Freq E-H are non-preferred. There are low power and mid-fed examples. TI - Traction Immune - is not a definate. They have limitations, i.e. not in P&C.
I'll try to find the circuit diagram for the internals and get someone far more knowledgeable than I to explain what makes them TI! J
Le coureur
16-02-2010, 01:47 PM
(16-02-2010, 01:31 PM)Jerry1237 Wrote: There are some caveats with TIs. Freq E-H are non-preferred. There are low power and mid-fed examples. TI - Traction Immune - is not a definate. They have limitations, i.e. not in P&C. The new digital ones will be apparently allowed in P&C; inbdeed I think there is already a trial site. Of course the French have used the predecessor UM71 in pointwork for many years and wonder why the UK refuse to do so. Basically immunity is due to the fact that the signal oscillates between a pair of frequencies which ar 35Hz apart, both of which need to be present / absent appropriately over a suitable time period and they are slow to pick as a result. The logic is that interference of a certain freqiuency that persists for a matter of a second isn't a transient; conversely the probbaility of two frequencies which are not harmonically related to each other or the 50Hz mains supply is vanishingly improbable.
PJW
22-02-2010, 06:37 PM
(02-02-2010, 08:00 AM)PJW Wrote: I thought I had a model answer to an exam queston on such a subject but can't immediately find it.Still not located it, but I did find this Track Circuit Audit sheet used for recording values obtained during site testing but also having some useful info re expected values etc.
PJW
22-02-2010, 10:46 PM
(16-02-2010, 01:47 PM)PJW Wrote: The new digital ones will be apparently allowed in P&C It is not the fact that the are digital that makes them useable in P&C, it is the fact that at about the same time, Bombardier have developed the "track coupling unit" to replace the tuner units in single rail applications. Given that the output of the digital unit is 100% the same shape and form as the analogue, all units are supposed to work with TTU, ETU or TCU.
06-10-2015, 04:31 PM
(This post was last modified: 07-10-2015, 12:38 AM by PJW.
Edit Reason: Trim previous repeated text
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(01-02-2010, 11:16 PM)Peter Wrote: I hope that gives you some idea of how they work, but please feel free to come back if you have other queries. Hi Peter, could you tell me how TCs is tested? and what could be the load for TCs for testing? Secondly, as TCs is directly connected to track with what value of Inductor and Resistor to simulate the track for testing purpose.
Hi Peter,
could you tell me how TCs is tested? and what could be the load for TCs for testing? Secondly, as TCs is directly connected to track, with what value of Inductor and Resistor to simulate the track for testing purpose. I am not sure quite how to interpret your questions; are these specifically asked for TI21 track circuits or more generally? I am also not sure what level of existing knowledge you have, so I am afraid this post will be more asking you to clarify your question than give an answer! However I shall give some information that might help us refine your request. TI21 track circuits are audio frequency track circuits,
I'll assume for now you are familiar with testing a dc track. Case 2 is quite similar to dc in some ways except that
I think that covers the first part of your first question; the second part may also have been covered to some extent, depending on precisely what you meant.
The second question is the one I don't really understand at all. The rails are continuous through the tuned zone so yes electrically the two track circuits are separated by an equivalent circuit which has both resistance an inductance. The dc resistance of 20m of rail is so low as to be negligible (however if it is jointed track with a fishplate joint bonded over by a couple of galvanised bonds then it isn't completely negligible); however the impedance presented at audio frequency is significant because of the inductance. I do not know numerically what it is; I suppose I could reverse engineer it from typical voltage readings, but really that is the concern of the product designer 30+ years ago; it is what it is and it is that value which dictates the TUs should be 20m apart on the typical 113 rail section. There is no simulation involved in real applications; I guess that some training schools which don't have the luxury of the space etc to have a 30m length of railway line may well have got some simulated circuit of resistor and inductor to get sensible values for trainee's experience, but I do not know what those values would be. Have I understood what you were actually asking?
PJW
07-10-2015, 04:51 AM
(This post was last modified: 07-10-2015, 06:40 AM by PJW.
Edit Reason: remove excess quoted text
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Hi Peter ,Thank you for all information !!!
Let me tell you in more detail of my problem.1) TCs what you called we named it as TCU Track Coupling Unit. It consist of a tranformer a resistor and a capacitor which is frequency dependent. Principle Track Coupling Unit (TCU) 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.It is a resonant circuit. 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. 3.5.2 Specificat ion Maximum rail to rail volts : 400 V DC / 275 V AC (RMS) Unit size : 140 mm H x 142 mm W x 203 mm L TCU to Track cable : 2 x 2.5 mm Sq. Copper cable, 2C-19 x 1.53 sq. mm (35 Sq.mm) copper cable or 50 Sq. mm equivalent aluminum. Max. Distance of TCU rail Connection to block joints. : 1 meter 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. |
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