Method and device for detecting a filling threshold for an electrically insulating reservoir containing an electrically conductive product, for example a printing ink

A method of detecting a predetermined threshold for filling, with an electrically conductive product a reservoir made of electrically insulating material having a storage cavity for containing the product and having an outlet channel for the product in which the storage cavity is disposed in a capacitive arrangement, said method comprising:

• defining a measuring procedure having an excitation step of applying, in periodic square waves, an electrical excitation signal to the capacitive arrangement and a capture step of taking a measurement signal from the capacitive arrangement, the electrical excitation signal being chosen so that the measurement signal has a characteristic varying substantially when the quantity of product contained in the storage cavity reaches the predetermined filling threshold;
• defining a conversion procedure including steps of identifying an instantaneous value of a quantity representing the characteristic, comparing the instantaneous value with a reference threshold representing the predetermined filling threshold, and deriving therefrom a first binary signal representing the situation of the instantaneous value with respect to the reference threshold;
• defining a digital filtering procedure including a convolution step of generating a third binary signal whilst effecting convolution product of the first binary signal and a second binary signal derived from the first binary signal by introducing a delay equal to a multiple at least equal to one times the period of the square waves;
• defining a processing procedure including a test step of deriving from the mean value of the third binary signal a binary value representing the situation of the quantity of product with respect to the predetermined filling threshold;
• and
• effecting at least one measuring cycle including steps of monitoring the measuring procedure, the conversion procedure, the filtering procedure and the processing procedure, and of capturing the binary value.