Structure and design
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3
Structure and design
3.1
Description
The Overfill Prevention Sensors consist of a probe which extends into the tank and the height
of which can be adjusted, a screw-in unit which carries the probe and a connection fitting.
The probe is sealed in the screw-in unit and can be moved and fixed within the adjustment
range. The screw-in unit is secured in place with a stuffing box fitting and additionally with a
locking screw. It is suitable for the pressure range from 0.67 – 2 bar (absolute). The sensor
(steel-enclosed PTC resistor) is located at the lower end of the probe. The PTC resistor in the
steel capsule is liquid-tight and gas-tight enclosed.
The connection fitting is a pipe fitting (direct filling) or a junction box with connection to the
wall fitting (remote filling). A 2-core connection cable (2 x 1 mm²) is installed from the junction
box to the wall fitting.
The Overfill Prevention Sensors are manufactured in probe lengths from 100 to 6,000 mm in
100 mm steps. The probe length is permanently engraved on the upper end of the probe tube
above the groove marking. The probe length represents the distance between the groove
marking on the upper end of the probe and the groove marking on the protective sleeve at
the height of the sensor.
3.2
Function
The PTC resistor is heated up after connecting the Overfill Prevention Sensor with the signal
amplifier of the Overfill Prevention Controller on the tank truck. After achieving a certain tem-
perature, the change in resistance caused by this process prompts a signal in the signal ampli-
fier "Overfill prevention device ready for operation".
The delivery of the liquid can now take place. As soon as the liquid reaches the sensor of the
Overfill Prevention Sensor, the heated PTC resistor is cooled down, thereby causing the re-
sistance to change; this prompts a signal "close actuator" in the signal amplifier. The actuator is
automatically closed and the delivery therefore is stopped.
The reaction time for the closing process from the time the liquid is recognised to the end of
the product flow must not exceed 5.5 seconds: from the recognition of the liquid by the sensor
up to the output signal of the Overfill Prevention Controller max. 2.5 seconds, from the output
signal of the controller to the end of the product flow max. 3 seconds. [prEN16657, Section
5.4.2]
