Measuring speed and distance for arriving trains and shunting locos at the railway station in dead-ends and other positions.
See also: Locomotive Radar SDM-76L.
SDM-76 is an all-weather specialized radar (measurer) for use in railway stations. Its functionality is an analogue of the parking sensor on the auto vehicle.
SDM-76 radar is based on automotive radar design, it operates at a frequency spectrum of 76 GHz, which does not require a license in Europe, the USA and many other countries. A frequency of around 76-77 GHz is belonged to W-band and is worldwide devoted to license-free applications like automotive cruise control radar.
Practical use of the SDM-76 requires that each radar has to be connected to the computer system of train traffic control. This is just as well as sensors on the bumper of a vehicle having to be connected to the vehicle parking system to inform the driver of an obstacle.
Speed and distance of arriving train are transmitted to the dispatcher (to the traffic control room) and locomotive driver, telling them on approaching a deadlock end on the exact track of the railway station. SDM-76 can also be used within a computerized safety system for automatic emergency braking of the train when it approaches a deadlock end track at unusually high speed.
Why SDM-76 radars
Earlier, laser range and speed meters were usually installed on deadlock ends of tracks. Due to the errors that are common for laser measuring devices when operating in adverse weather conditions such as optical noise of heavy rain, snow, smoke, and dust, — they have to be replaced with all-weather radar SDM-76.
SDM-76 operates in the millimeter wave range (W-band), which is insignificantly attenuated by fine substances such as smoke, dust and precipitation. In other words, these 76GHz radars have virtually no weather restrictions at short distances. At the same time, the radars have a very narrow quasi-optical beam which allows monitoring only those objects that are on the exact railway track, not reacting to trains arriving on the adjacent track or passengers walking on the platform.
Typically, SDM-76 radars are equipped with 60 cm diameter antennas. This ensures the desired antenna pattern is as narrow as 4.3 m at a distance of 500 m.
For example, the distance between the axes of tracks in European railways is from 4.1 to 5.0 m according to national standards. Thus, the radar will not “see” the train on a neighbour track. In the real environment of stations with deadlock end tracks, the length of platforms is not more than 500m (500 m = 20 passenger carriage train length). The distance of 500 m is enough to automatically stop a passenger train from a speed of 60-70 km/h to zero.
SDM-76 radars can be equipped with an antenna of diameter from 10 cm to 90 cm, in accordance with conditions of SDM-76 radar use in a specific project. The larger the diameter of the antenna, the narrower the radar beam (also known as antenna directivity pattern) is.
SDM-76 Interface and Data
SDM-76 transmits data on the speed and distance of the train (as the target) in response to a request from the hub (LAN concentrator) of the railway operator’s server. The server requests data from radar during all times of train occupies the exact track. In case there is no train, data are not transmitted. This has been done to not to overload the railway LAN with currently unused data.
Each set of data transmitted from the radar to the traffic control server includes the following information:
• speed of the target in km/h
• distance to the target in meters
• service information about the availability of the radar
• service information that data goes beyond the measurement ranges (in case of very high speed of the target).
• Connection Interface: 1000Base-Tx UTP Ethernet.
|Distance measurement range||1.5 – 500 m|
|The max distance measurement error||+/- 0.25 m|
|Speed measurement range||1 – 100 km/h|
|Speed measurement range||max 1.0 km/h|
|Radar frequency||76.5 +/- 0.15 GHz *|
|Output power at Swept frequency modulation||10 mW|
|Antenna diameter||600 mm|
|Beam width||0.42 degrees|
|Diameter of a spot at 500 m||4.3 m|
|Output Interface||1000Base-Tx UTP Ethernet|
|Measurements update time||20 ms|
|Consumed electrical power||20 W|
|Environment protection class||IP65|
|Environment operating temperature, °С||-45 to +55 °С|
* 76.5 GHz frequency is belonged to W-band and is worldwide devoted to license-free applications like automotive cruise control radar. 94 GHz version is also available by request.
Deadlock end track monitoring
SDM-76 control zone corresponds to a circular cone with an angle of 0,5° and a height of up to 500 m. The length of the meter control zone along the direction of movement is controlled from 1.5 m to 500 m, width of the control zone is from 0.01 m to 4 3 m.
The radar unit is designed to be mounted on a vertical pole (mast) with a diameter of 50 mm to 120 mm. The radar has to be installed on the centre of the track at the height calculated as 1/2 of the antenna pattern diameter on the max specified distance. In the described case, the antenna pattern on 500 m is 4.3 m in diameter. Thus, the radar installation height is 2.15 m.
• Radar unit for measuring distance and speed of a train,
• Antenna to form a narrow beam pattern,
• Alignment-fixing device for fixing the meter and the possibility of precise adjustment of the antenna to the monitored railway track.