Railway Signal Engineering

  Signal Conditioning Card  (SCC) 1) There are two SCC cards in SSDAC.  2) SCC 1 is connected to TX 1 and RX 1 coils. 3) SCC 2 is connected to TX 2 and RX 2 coils. 4) SCC 1 generates carrier signal 21 KHz and feed it to TX 1 Coil. RX 1 receives this signal and send back to SCC 1 Card. 5) SCC 2 generates carrier signal 23 KHz and feed it to TX 2 Coil. RX 2 receives this signal and send back to SCC 2 Card. When there is no train there is a phase difference of 180 degree between the signals of TX and RX coil. This phase shift can be monitored by means measuring 2.2 V DC if there is no wheel on device.The range is 2.0 to 2.5 volts. If this voltage is in the range,it means that SCC card is transmitting correct frequency, receiving  correct frequency and phase difference between  Tx and Rx are 180 degree. If during installation of SSDAC you are not getting this 2.2 V DC, reverse the RX Cable polarity in Location box for getting the same. When you place Dummy wheel on ...

      In this blog you will learn how Tx coils are connected to SSDAC unit. 1) There are 8 cards in SSDAC unit.( I will explain in detail later) Please remember  that  Tx and Rx coils are connected to SCC 1 and SCC 2  cards only. These coils are not connected to any other card. 2) Tx coil 21 KHz is connected to SCC 1 and Tx coil 23 KHz is connected to SCC 2. 3) These coils are connected through MS Coupler (MS 1). 4) MS 1 coupler is connected behind SSDAC Unit.There are four conductor in MS 1.  5) Color of these four conductors are BLU E , ORANGE , GREEN and   BROWN . 6) Blue and Orange are connected to TX 21 in Location Box 7) Green and Brown are connected to TX 23 in Location Box for RX Coils I will discuss in my next blog.Please feel free to raise your queries.

 1)  We know that in CEL SSDAC, there are two TX coils , one 21 KHz and another 23 KHz. 2)    Similarly there are two RX coils,   one 21 KHz and another 23 KHz 3)  From Each coil , two conductors are coming out and their color are Red and Black. 4) Between these two conductors, we can measure the Resistance with our Multimeter. This value is Coil Resistance of this coil. 5) Before measuring Coil Resistance,  open the link of both conductors from ARA terminal.Then only you will get correct value. 6) For TX Coils ,Resistance of these coils  must be less than 1 ohm. If you are not getting this value, replace TX Coil,it will give you failures. 7) For RX Coils, Resistance of these coils must be between 2 ohm and 3 ohm. 8) After measuring Coil Resistance. terminate these conductors on ARA Terminals as mentioned in below picture. 9)       When we measure voltage  at  TX 1 or TX 2 ,it will come between (30 V- 40 V ) AC....

          Main component of Axle Counter is track devices which detect the movement of train wheels over it. Now the first question is where should  we fixed this device if we are using it for Block Proving    ( Along with UFSBI or BPAC).You will not get the answer of this question in any book. One thing is clear, it must be between Advance Starter and Home Signal.First find out  Block Overlap of that station.For Colour light signalling,block overlap is 180m . Therefore we will measure 180m from Home Signal towards station and mark the position for installation. While marking this position make sure that Axle detectors should be at least 13 m from Advance Starter towards HOME SIGNAL so that Axle counter fail whenever Train crosses ADVANCE STARTER and enter Block Section. CONCLUSION - Axle detectors must be placed between HOME SIGNAL and opposite ADVANCE SIGNAL at a distance 180 m from HOME SIGNAL and 13m from ADVANCE SIGNAL. Please remember f...

  Axle counter is a device ,used to detect presence of train over on a specified portion of track.This specified portion can be any Platform line, Point zone area or Block section. The digital axle counter produced by CEL is very popular in Raillway because it is easy to learn,Easy to maintain and easy in fault finding.  It is widely called SSDAC in railway.I am giving block diagram of SSDAC below. 1)  In this system one set of axle counter is provided at Entry End and other set is provided at Exit End.Both sets are connected to each other through Quad Cable.Only two conductors of quad (Half Quad) are required. Now I will tell you what are the components of one set of axle counter. First part of SSDAC is TX and Rx coils mounted on rail. Second part is SSDAC unit in the Location Box. Third part is VR-PR Box in the Location near the SSDAC unit.It has two relays VR and PR.If the section is clear VR will pick up.VR relay will drop only when there is train in the section or SS...