BS EN 13922:2011 pdf download – Tanks for transport of dangerous goods — Service equipment for tanks — Overfill prevention systems for liquid fuels
6.1 Overfill prevention system working characteristics
6.1.1 Overfill The overfill prevention system shall be an electronic system, gantry based and gantry operated. The interface wiring shall be suitable for a two-wire or a five-wire overfill prevention system and the gantry based controller shall automatically detect the difference between either overfill prevention system through a standardized 10 pin plug and socket see Figures A.2 and A.3
and perform its functions. Electrical specifications for the interface are included in Annex A. If no wet sensor or system fault is detected, the controller shall give a permissive to permit loading to begin. Upon an overfill condition or the detection of any overfill prevention system or controller fault, the controller shall switch to non-permissive.
The overfill prevention system shall be fail safe and shall be self-checking. The effective cycle time between self-checks shall be less than the overfill response time. The overfill prevention response time shall not exceed 700 ms. The overfill prevention system shall be capable of handling up to and including the following number of compartments for each type of installation:
two-wire system 8 compartments;
five-wire system 12 compartments.
6.1.2 Bonding The overfill prevention system shall provide an earth static bonding connection from the gantry to the vehicle chassis via the cable and connection plug and socket and shall continuously verify this connection throughout the loading operation. Should any fault be detected or the electrical resistance of the connection exceed a maximum of 10 kΩ, the gantry controller shall switch to non-permissive.
6.1.3 Severe environmental condition Where the overfill prevention system is subjected to temperatures outside the specified temperature range all applicable temperature values shall be extended. All other requirements shall remain unchanged.
6.2.1 General Any of the following types of sensors may be used:
6.2.2 NTC thermistor, two-wire optic or other compatible sensor Thermistor sensors shall have a negative temperature coefficient (NTC) and shall work at any temperature in the range from – 20 °C to + 50 °C. Thermistor sensors have a warm-up time which shall not exceed 75 s with the thermistor sensor at an ambient temperature of – 20 °C. NOTE Optic sensors have a negligible warm-up time. Two-wire sensors can be used on vehicles with no more than 8 compartments. The overfill prevention controller shall always monitor 8 sensors and stop all loading if any sensor detects an overfill. Vehicles equipped with two-wire sensors with less than 8 compartments shall employ an electronic dummy sensor for the unused channels of the controller. The electronic dummy sensor shall generate a permissive signal when it is connected to a controller. The signal shall correspond to a wave form as shown in Figure A.1 with the values according to Table A.4. A two-wire optic or other compatible sensors shall work at any temperature in the range from –20 °C to +50 °C. When connected to a gantry controller, a dry sensor shall generate a permissive signal, which shall correspond to a wave form as shown in Figure A.1 with the values according to Table A.4.
6.2.3 A five-wire optic or compatible sensor A five-wire optic sensor or other compatible sensors shall work at any temperature in the range from – 20 °C to + 50 °C. When connected to a gantry controller, a dry sensor shall generate a permissive signal, which shall correspond to a wave form as shown in Figure A.1 with the values according to Table A.1.
6.2.4 Sensor circuit A sensor circuit shall comply with the requirements according to 6.2.2 and 6.2.3 as applicable.
6.2.5 Response time The reaction time from sensor going wet to the change of state of the signal at the interface socket shall not exceed 250 ms.
6.2.6 Materials of construction The manufacturer shall provide with the equipment a full material specification for those parts that may come into contact with the liquid.
6.2.7 Electrical requirements At the interface each sensor or sensor circuit shall be suited for controller’s intrinsically safe parameters. The electrical connections of the 10-pin-socket shall comply with Figure A.4 for a two-wire-system and Figure A.5 for a five-wire-system. The socket shall comply with Figure A.2.