Railway Out of Gauge Detector – System Overview: This is a system to detect and prevent larger surface sized rolling stock from entering tube sized tunnels, thereby preventing a collision with the tunnel mouth. The system is based upon three ‘U’ shaped tubes, which are suspended above the tracks from gantries leading to the tunnels. The glass tubes allow sufficient clearance for the smaller tube-type rolling stock to pass underneath, but will be broken by a taller surface stock train. An electrical connection through the glass tube is broken when tube itself is broken, and this sends an indication to the signalling system, which will halt the train before it reaches the tunnel mouth by maintaining a suitably positioned trainstop in the up position.

Existing Architecture:  The Out of gauge detector is equipped with three tubes incorporated in the signalling circuits and operates from 100V signalling power supplies reduced to 12V, via step down transformer to specification SE1080, at frequencies of 33.3, 50 or 125 Hz. The operating circuit draws a nominal current of 50mA and a maximum current of 200mA, for continuous operation. The tube has an electrical resistance of not more than 0.25 Ohms. Once the tube is broken, the circuit can not be immediately re-estabilshed.

On the Jubilee line, an existing Out of gauge detector is located at Finchley Road.On Piccadilly Line, Out of Gauge Detectors are located at on the eastbound road west of Barrons Court, and on the westbound road east of Hounslow West.Refer to the existing circuit of Out of Gauge detector at Finchley Road.

New System Overview: The TBTC system will interface to the existing Out of Gauge Train Detector and associated signalling circuits on the Jubilee Line at Finchley Road.

The existing surface stock Out of Gauge Detectors will be retained. The existing trainstops at Finchley Road will be removed. New flashing red lights will be installed at the south end of Finchley Road southbound JL Platform.

New Interface:In the event that a detector is operated, the VCC tracks associated with the detector will be closed and red flashing lights activated.

Refer to Out of Gauge Block diagram below:

Control: The red flashing lights will be illuminated when out of gauge detector is operated. In addition, trainstops at Barrons Court shall be raised when the out of gauge detector is operated, to prevent District line trains entering the eastbound Piccadilly Line Platform.

Detection: A Contact of the out of gauge relay will be input to the SCS in a fail-safe manner.

Electrical Description: The relay circuits between SER and IMR, will be powered at 110v 50Hz emanating from TBTC Power supplies.

Refer to the Interfacing circuits below for Out of Gauge Detector:

1. Out of Gauge Detector is a Emergency Stop Device.

2. The existing Out of Gauge Detector status will be repeated to TBTC SER by picking up a repeater in TBTC SER using the contacts of existing Out of Gauge Detector relay from IMR.

3. The repeater circuits will be powered from ESD busbar as it is emergency stop device and During the nightly IMC test, the ESD busbar (called ‘BX110(S/W)(EXT)’) is de-energised and re-energised, and the ESD relays are checked to ensure they operate correctly.

4. The Relay Rack shall continuously indicate the status of the Out Of Gauge Detector to the SCS Electronics Rack. A Contact of the out of gauge repeater relay will be input to the SCS in a fail-safe manner.

5. The Relay Rack shall illuminate the flashing red lights associated with the Out Of Gauge detector while the Out Of Gauge detector is detected activated.

6. Back contacts of the Out of Gauge Detector repeater relay are proved in red flashing light circuits to activate the red flashing light when Out of Gauge detector is operated.

7. If the detector is out of use for a long period of time, the out of gauge detector can be overridden in the VCC (ESD Override) and the RFL could be turned off by isolating it via MCB.

In the event of SCS failure: In the case of SCS failure, out of gauge detectors in the SCS area will be deemed to have been operated. Which will lead to tracks being closed, The RFL will start flashing, Controlled trains travelling in the affected area at time of failure will come to a stop.

For more information on the functionality of the Out of Gauge Detector on the Jubilee Line, refer to Mixed Mode Area Functional Description – 3CU 00550 0146 DSZZA, Rev. 6.

‘V’ Style Frame Chairlock Point Circuits

The Point Control, Lever Lock and Indication circuits for Chairlocks are identical to the Four  Foot point circuits already discussed.

Detection

Unlike Four Foot points, a Chairlock layout uses two separate and independent detection units, one for each rail switch. Each unit proves that its corresponding switch is either fully home and locked or open sufficiently.

The four contacts in each unit are labelled four, three, two and one with the number four contact always drawn at the top as shown in the contact arrangements for both layouts Figs 5.2 and 5.4.

If the right-hand switch is closed when the points are Normal (Fig 5.1) this will be a Normal contact. It follows that the left-hand unit is the opposite (Fig 5.2).

Right hand unit

If the right-hand switch is open when the points are Normal (Fig 5.3) it will be a Reverse contact. It follows that the left-hand unit is the opposite (Fig 5.4).

left hand unit

Although there are four contacts in each unit, contact number one is used exclusively for the control of the WL and therefore there are only three contacts available for the detection circuit. Number two contact is used for the open switch detection and contact numbers three and four are used for the closed switch detection.

The detection circuit needs to check the contacts in both units before picking up the WKR. If the left-hand turnout above is in the Normal position (Fig 5.3) the right-hand unit proves that its associated switch is open a minimum of 3 1/2″ (89 mm). The left-hand unit proves that its switch is both fully home and locked.

Fig 5.5 below shows a typical detection circuit for a left hand turnout, single ended set of Chairlocks. The BX supply to the WKR is always fed to the right-hand unit on terminal 3:3 (this is also the same for a right-hand turnout) from here it is looped to 2:2 on the same unit. The feed then goes to 3:3 on the left hand unit to the WKR. The NX returns via 4 and 4:4 on the left hand unit.

As with Four Foots the looping in the units is there to change swap the BX and NX supplies over in order to drive the three position WKR Normal or Reverse.

Left-hand turnout, single ended Chairlock detection circuit

It should be noted that there is no WL proving contact in the circuit as it is indirectly proved via the mechanical design of the Chairlock unit. The contact box is sprung to the neutral position and relies on the WL to maintain pressure on the cam follower arm which in turn follows the profiles of the lock and switch detection cams to make the contacts.

If the WL is not fully de-energised it will not apply pressure on the cam follower arm and therefore the contacts will remain broken (regardless of whether the points are actually mechanically home and locked).

Fig 5.6 below is an example of a left hand turnout, double ended layout detection circuit.