Artykuły :: Transport :: Conference papers
|Issues of monitornig systems and industrial TV|
Availability of a broad game of monitoring equipment on the marker allows construction of an observation system that is both flexible in expansion and functional. Selection of appropriate components of such a system (cameras, displays, recorders, transmission media) is based mainly upon the assessment of equipment quality and work parameters.
The camera point consists of several components. A basic component is a camera i.e. a device provided with a visual transducer, either monochromatic or color. The cameras are equipped with lenses in order to adjust the transducer’s capacities to the work conditions (lighting, distance and observation field).
Fig.1. Instances of a camera and lens with automatic diaphragm
Add-ons ensuring adaptation to the environmental parameters of camera operation are housings, heaters and rotational heads.
Lenses tat are available on the market may be divided as follows:
1. with fixed diaphragm,
2. with movable diaphragm,
- fixed focus
- variable focus
- with automatic diaphragm and manual focus
- with automatic diaphragm and electrical focus
The installation places determines selection of appropriate lenses. Lenses with fixed focus and fixed diaphragm are used at the locations where no change of viewing angle during camera operation is necessary. Knowledge of operation parameters before a camera is installed is also important (monitored surface – depth of focus, lighting intensity).
Lenses with manually regulated focus (and diaphragm) are more versatile. They may be used at locations where it may be necessary to adjust the position of camera during its operation.
A drawback of lenses with fixed and manually regulated diaphragm (and focus) are “narrow” operating (lighting) conditions, depending of camera parameters. Advantage are cost of these lenses and their high reliability during operation.
Cameras with mechanically regulated working parameters feature high versatility. Lenses with automatic diaphragm (Auto-Iris) controlled by the camera itself based upon lighting intensity, find their application in variable conditions (for example in very sunny places).
Cameras with automatic diaphragm and electrically controlled focus are the most advanced of industrial cameras. In addition, they are equipped with rotating positioners thus allowing monitoring of very large areas. Variable focus enables large zooms till x27. Such cameras find their application in monitoring of urban areas, department stores, industrial workshops and railway stations .
Spreading and low prices of wireless technology appliances resulted in appearance on the market of wireless cameras and wireless visual and sound signal transmission systems (up to 4 tracks in one channel). Reach of such devices, amounting, according to 2,4 GHz standard up to 400 m in open areas , results in a reduction of cable infrastructure, especially when local grid may be used for power supply to the cameras.
Till recently, the television systems used excusively CRT displays. Today LCD displays are more frequently used, although their durability is not as high as that of CRT displays. Implementation of LCD displays is caused mainly by the tendency to improve the systems users’ working conditions, and the LCD displays, for guaranteed safety, require additionally a mechanism protecting them against picture freezing. For this reason, complete disappearance of CRT displays is not to be expected very soon, especially at places where the human life is at the stake. An important item during design of monitoring systems is planning of positioning of displays in the observation room. In this respect, very helpful are various types of hangers or poles for display mounting, enabling such positioning of the screen that it is away from direct sunlight that may lead to partial or total loss of picture visibility.
Fig.2. Instances of pole hangers
Recorders available on the market may be divided into two groups. First are frame recorders, recording on a magnetic tape. Nowadays, because of a range of drawbacks, they are almost entirely replaced by the digital recorders. Their basic disadvantage are long search time and short archiving time on a single carrier, as well as high cost of the device itself and high operating costs.
A second group of recorders are digital recorders, that may be divided into computerized ones (consisting of a PC equipped with special cards for connecting cameras), and autonomous ones. Both these design use hard disks as recording medium. The size of hard disk in autonomous recorders are limited mainly by the manufacturer (forced by the device performance).
Fig.3. DVR Cards (4 and 16 channel) – component of a computerized recorder
In the case of use of a computerized recorder the advantage is lack of limits in the storage capacity. It is possible to use network solutions, such as a disc array or creation of a local independent disc array (in the computer) using a built-in or additional RAID controller to create a continuous data space.
An instance recording time from 4 camera points on an autonomous recorder equipped with a hard disk with capacity 240 GB is ca. 50 h . This approximate time value is caused by picture compression where volume of one frame may vary. It depends of picture complexity, as less place is needed for the storage of a picture with small number of details, dark or overexposed. The quantity of data composing one frame is also affected by the applied method of picture compression (each frame separately or recording of changes with a wider spread key frames with full picture information). The quality of recorded picture depends also of assumed compression ratio. A very good quality is assumed with picture readability of 640 vertical lines (tests performed using special patterns). Such a resolution allows to read a license plate. Fig.4 presents instances of autonomous recorders.
Fig.4. Autonomous recorders – 4 and 16 inputs
Most of recorders is equipped with alarm inputs and outputs. They enable control of external equipment and switching on the recording at the signal detection on the input. The outputs may be configurable as relay contact outputs or voltage outputs (with low load about 50 mA). An instance of application may be also cooperation with an alarm system (definition of movement detection in a remote area enables replacement of a movement watchdog with cabling at a long distance from the alarm center), or warning system (for example a system for a large railway station – replaying of the message “please withdraw from platform edge”). Alarm outputs may be also used for a full duplex system (using two recorders where one is a basic one and the second a standby) to switch on the standby recorder when the basic one becomes out of order.
1.4. TRANSMISSION MEDIM
Requirements for transmission medium includes mainly maximum reach and transmission reliability. First parameter is established using cable attenuation (maximum length where a proper communication is possible – with acceptable noise level). For copper cables this distance is 6 km. Now very often for transmission purposes optical cables are used, enabling transmission up to 70 km without a repeater. Price of the optical wire is also a considerable advantage, as it is lower than that of copper cables at the higher reach and higher throughput. Drawbacks of this modern medium are costs of transmission equipment (special converters) and costly repairs of damaged cables (welding).
Optical converters may be provided with additional functions, for example they enable transmission of signal in the following standards RS485, RS232, TTL, sound channel (also bidirectional) as well as contact status (programmable NO, NC). An instance of such a converter with bidirectional RS485 and four contacts (two in each direction) is presented on Fig.5.
Fig.5. Instance of an optical wire converter
An alternative for wire systems is wireless picture and sound transmission systems (and data). Radio devices use mostly two frequencies 2,4GHz and 5GHz. Railway regulations accept use of such devices. Sometimes it is an only economically justified possibility to install a camera point (as well as other devices) at a location where the power supply is available and the costs of telecom cabling would be very high. Available transmission coding standards guarantee safety at the level that is sufficient for wireless picture transmission systems.
2. SELECTION OF SOLUTIONS OF INDISTRIAL TV FOR RAILWAYS
The most important problem encountered during selection of cameras and housings is fulfillment of environmental requirements. Cameras and elements placed outdoors have to operate correctly at the temperatures ranging from -40 to +55°C. For negative temperatures heaters may be used (special camera housings with built-in heater and thermostat system). Containers (trackside boxes) have usually resistance heaters. The upper temperature limit may be fulfilled by using fans. Parameters of lens and housing operations are similar to those of cameras. Fig.6 shows placement of equipment inside a trackside cubicle with installed heating element using resistance heater (bottom right part of cubicle).
Fig.6. Train end detection cubicle equipment
2.1. TRAIN END DETECTION SYSTEMS
Location of cameras is of special importance for train end detection and for level crossing monitoring system. Visibility of train end signals may ensure their proper reading. This is a problem, especially on stations, where the station geometry causes cameras blinding by sunlight at certain hours of day and where bad lighting conditions exist.
Blinding may take place also on two-track lines with two oppositely placed camera points at an angle close to the track axis. Cameras operating at the train end detection points may be blinded in winter also by the end signals, because of point type of light source and prolonged accommodation of camera. This may lead to the unreadable picture causing “white spots” on the display screens at the certain section of train travel.
Various site conditions at each system installation point result in a lack of possibility to state the uniform requirements for train end signal visibility section. The main indicator of camera vision field should be opinion of traffic controllers using it at the certain location. Because of changing lighting conditions over the seasons (level of lighting, atmospheric precipitations) a possibility of camera position correction should be provided. Fig.7a, b and c presents blinding, that may occur when two trains pass each other on a two track line and go straight to the camera, and visibility of reflective train end signals (classic plastic reflective triangles used on railways and triangles from reflective foil) from two locations with infrared lighting.
Fig.7. Instances of a picture from camera: a) blinded by a coming train; b), c) with additional lighting with infrared emitters –visibility of reflective endings
2.2. VEHICLE PASSING OBSERVATION SYSTEMS
Monitoring of vehicle passing is an auxiliary system that may fulfill safety conditions. Variety of vehicle geometry causes the companies offering vehicle observation systems to execute special flexibility in designing. Change of road cross-section or number of tracks results in a necessity to re-analyze the positioning of camera points and their equipment (lenses, infrared emitters). It is necessary to place and direct the cameras in such a way as to enable the operator to see both the level crossing and appropriate track sections upstream it before he makes a decision about lowering the barriers. In addition, when selecting the observation system it is important to ensure readability of vehicle license plates. This is a requirement protecting the railway operator and gatemen on the remotely controlled level crossings without direct visibility in the case of barrier damage and accidents.
An additional issue affecting the traffic safety both on the road and on board of the vehicle is lighting of level crossings. The regulations in force require lighting of a remotely operated level crossing with use of industrial TV at the level of at least 30 lx . These are very high values and difficult to comply with. This value should be reduced because of parameters of presently available cameras and for the sake of traffic safety. Contemporary cameras enable recognition of an object moving at night through an unlighted level crossing (lighting intensity from 0 to 1 lx – the closest light is a mercury lamp at the distance of ca 10 m from the crossing).
Readability of license plates on the level crossing may be achieved using infrared radiator lighting – light with wavelength invisible for human eye. This will enable much better lighting of important places with simultaneous lack of possibility of blinding either the car or train drivers. Level crossing lighting may be reduced to much less values – at the acceptable level for normal level crossings i.e. 10 lx. Fig.8 shows differences between two cameras observing surfaces with different lighting intensity.
Fig.8. Instances of level crossing lighting – lighting with lower intensity on the left
An additional advantage if infrared radiators based on diode matrix supplied with 12 V is a possibility of its direct connection to the standby power supply system. This enables maintaining the level crossing lighted at the good level of readability from cameras in the situation of power supply voltage decay.
Also voice communication systems are installed at level crossings expanding the system functionality with a possibility of information exchange with road users.
The presently available system solutions enable operation of cameras practically without lighting. Use of modern lighting solutions will enable enhancement of system readiness at the power supply voltage decay and will remove discomfort of the drivers related with too much light while maintaining sufficient conditions for improvement of camera operation .
Revision of regulations governing level crossing lighting is justified and supported by tests. Further tests will enable minimum intensity of light for railway level crossings controlled from remote, where the observation takes place through industrial TV systems.
 Rozporzadzenie Ministra Transportu i Gospodarki Morskiej z dnia 26 lutego 1998r.
 PN EN 50125-3: Railway applications – Environmental requirements for the equipment – part 3: Equipment for signaling and telecommunications
 VESTENICKĂ P.: Optimization of Selected RFID System Parameters. AEEE 3, 2004, No. 2, pages 113-114.
 VESTENICKĂ P.: Increasing of RFID systemread range. AEEE 5, 2006, No. 1-2, pages 171-173.
Faculty of Transport, Silesian University of Technology