Warning device for indicating critical condition of starter batteries in vehicles

Claim 1

A warning installation for indicating a critical charge condition of starter batteries in vehicles, especially in motor vehicles, according to the areometer principle, characterized by an areometer housing means connected with the interior space of a battery housing means by way of aperture means, float means movable in said areometer housing means, a coil disposed in said areometer housing means and protected against the battery acid, warning means connected to said coil, a core of magnetizable material connected with said float means, said float means being arranged for sinking in said areometer housing when the acid concentration falls below a predetermined level so that said core is immersed within said coil, said coil being responsive to the immersing of said core therein for changing the inductance thereof and triggering said warning means to provide at least one of an acoustic and optical warning signal indicating that the acid concentration of the battery is below the predetermined level, the coil forming part of a tuned circuit of an oscillator means connected thereto, said tuned circuit being tuned to resonance upon immersion of the core into the coil, thereby causing the oscillator means to generate a signal with a frequency corresponding to the resonance of the tuned circuit, the signal being amplified in an amplifier connected in the output of the oscillator means and the amplified signal triggering a warning signal in an indicating means connected to the amplifier, a delay means being connected in front of the indicating means which prevents the triggering of a warning signal as a result of a sinking of the float means caused by vibrations.