A first electrode (6) is placed inside the distribution circuit and the second electrode (7) is placed outside the circuit near the nozzle opening so it is immersed in the liquid jet projecting from the nozzle upstream of its dispersal, thus measuring the flow of liquid from the nozzle. The device has a distribution circuit (1, 5) for the liquid (2) from a reserve (3) to the nozzles (4). At least one pair of electrodes (6, 7) designed to be in contact with the liquid are placed at each nozzle and are attached to means of alarm (11) to signal when the nozzle is blocked. The first electrode is placed inside the distribution circuit using a fixed support with easily reversed connectors, placed between two of the circuit elements. The second electrode is directly attached to the nozzle near its opening. The nozzles are supplied with means of fixing the electrodes, with the first electrode protruding from the nozzle body at its end near the inside of the circuit and the second electrode is carried by the other end of the nozzle body. The electronic means of comparing the analog information from the electrodes and from the instructions are placed between the electrodes and the alarm, so it can send a signal to the alarm when a threshold signal is reached, obtained from the instructions recorded by the user onto a recording device (18) via a collector (16). The means of comparing are means of transcribing analog data relative to real variation in the liquid jet from the nozzles into digital form transmitted to the alarm. The means of comparing are associated with means of identifying each nozzle to inform the alarm which data is for which nozzle. These means of identifying the nozzle are sequential addresses for each nozzle defining their position in the spray assembly. The nozzles are grouped in sections by a respective inlet valve. The alarms and control units are placed at a control point together with data from the means of comparing, recording and identifying the nozzles. The electrodes are connected by wires to this control post, which also includes the means of data treatment. Alternatively, a number of treatment units are each placed near their respective groups of nozzles and data is transmitted to the control point through wires, fibre optics, or ultrasound, infrared or radio transmitters. The means of control is designed so when a group of nozzles is shut down by the operator, the alarm is not triggered spuriously by the apparent blockage of these nozzles.
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