Abstract: A method of measuring the impedance of a sensor by applying a sine-shaped AC voltage and transforming the response signal proportional to said impedance into a DC voltage such that even for very little measured voltage highest linearity is present. The method comprises the steps of generating a square wave voltage together and in synchronism with said AC voltage, applying said AC voltage to said sensor impedance, filtering the resulting AC voltage and bringing it into a defined phase relation to the square wave and rectifying the AC voltage by means of a switch controlled by said square wave. The rectifier circuit is a low-pass circuit having a grounded resistor which by said switch intermittedly is short-circuited.

Abstract: A metal detector is disclosed which has a transmit coil, a receive coil, and circuit means for detecting metal objects due to a change in the magnetic coupling between the coils. Circuit board arrangement techniques are disclosed which enable the close placement of the transmit and receive coils and the circuit board, thereby allowing packaging of the metal detector in a small package. A low battery voltage indicator circuit is provided to warble an audio indicator signal to indicate sufficient battery voltage. In the event the battery voltage drops below a certain level, the warbling of the indicator signal ceases and a steady tone is generated thereby indicating a low battery voltage condition.

Abstract: In the disclosed device, a signal forming circuit produces a signal having a frequency corresponding to the voltage of a power source. A level detector detects the level of the voltage of the power source and is arranged to produce a signal when the voltage of the power source drops below a predetermined level. A control circuit coupled to the signal forming circuit is arranged to change the frequency of the signal produced by the signal forming circuit in response to the signal produced by the detector. An indicator operates at the frequency of the signal produced by the signal forming circuit. In a specific embodiment, a detector detects whether the voltage of a battery is at and below a first level, between the first level and a second higher level, and at and higher than the second level.

Abstract: The present invention relates to apparatus and methods for measuring the different potential drops in electrochemical cells (EC), i.e. measuring independently the following: anodic and cathodic over potentials (IR free) each half cell ohmic solution resistance and each half cell solution potential drop (IR drop). This invention is applicable to electrochemical cells such as: batteries, electroplating baths, water electrolyzers and other EC operating continuously.

Abstract: When the battery voltage is sufficient, and not nearing the point of insufficiency, a light-emitting diode is steadily illuminated. As the battery voltage decreases, the steady component of illumination decreases and also, when the decrease has proceeded to a certain extent, a superimposed pulsating component of illumination is introduced, causing the illuminated LED to begin to flicker, informing the user that the battery voltage is nearing insufficient values. As battery voltage drops further, the steady component of illumination ceases altogether, and the flicker converts to on-off blinking, indicating that the battery voltage is at the verge of an insufficient value. When the battery voltage drops fruther, the LED ceases to be illuminated. During part or all of the flicker phase, and/or during part or all of the blinking phase, the frequency of the pulsating component of illumination progressively increases with decreasing battery voltage, to create an effect of increasing urgency.

Abstract: Apparatus for indicating the level of the electrolyte in a battery cell. A three-electrode sensor probe having the electrodes partially embedded in an electrically insulating housing suspended in the electrolyte so that a portion of the probe is immersed in the electrolyte. The electrolyte provides the only conduction path between the electrodes so that the resistance between the electrodes varies according to the level of the electrolyte. An AC or pulsed DC sensing signal is applied between two of the electrodes and an output signal related to the level of the electrolyte is produced. A polarizing current is applied to the other electrode to prevent the buildup of surface contamination on the two sensing electrodes due to the sensing signal.

Abstract: A system for determining the presence or absence of coolant liquid as well as for monitoring the effectiveness of corrosion inhibition of the liquid includes a high impedance differential amplifier to which two electrodes, adapted to be immersed in the liquid, are connected. The high impedance differential amplifier measures the d.c. potential of the electrodes as an indication of the effectiveness of the corrosion inhibition characteristic of the liquid. The output of the amplifier is connected to a detector which in turn is connected to conventional indication means such as a light emitting diode. A conventional power source provides positive and negative power to the amplifier. The output of the amplifier is also connected to one of its two inputs through a feedback network comprising a capacitor and a resistance which includes the resistance between the electrodes.