A proximity sensor oscillator, having a resonant circuit in which the power loss is inversely related to the distance of a conductive body from a probe containing a part of the resonant circuit, produces an oscillating output signal in the resonant circuit with a peak amplitude that varies with power loss and distance. A power source provides either the current or the voltage component of electrical power at a substantially constant value independent of changes of resonant circuit power loss and is periodically switched to the resonant circuit to provide an average input power thereto. The power loss of the resonant circuit loads the source, and thus the other component of power oscillates within the resonant circuit at a peak amplitude linearly related to the inverse of the power loss. A control circuit is responsive to the phase of the oscillating component to maximize power input to the resonant circuit by applying the fixed power component substantially only throughout each alternate half wave of the oscillating component having the same polarity sense as the one component. Over the operating range where the inverse of the power loss has a linear variation with distance, the peak amplitude of the oscillating component varies linearly with distance. A detector circuit responsive to the amplitude of the oscillating component provides an indication of distance.
A proximity sensor oscillator is disclosed having controlled charge. The proximity sensor oscillator includes a resonant circuit which oscillates at a frequency determined by the components of the resonant circuit and with a power loss that is inversely related to the distance that a sensor element of the resonant circuit is to a conductive object. The peak amplitude of the resonant circuit varies with power loss and therefore measurement of this parameter provides an indication of the proximity of the conductive object to the sensor element. Power is provided to the resonant circuit by metering a fixed charge to the resonant circuit just before the peak of the resonant circuit voltage by means of a transistor switching circuit. By operating the oscillator within a range where power loss is inversely linearly proportional to the distance of the sensor element from a conductive object, the peak amplitude of the resonant circuit varies linearly with distance and hence, when detected, provides an indication of distance between the sensor element and the conductive object.
An oscillator/demodulator circuit arrangement for an inductive proximity switch with a transistor amplifier stage having an input circuit containing an attenuatable resonance circuit and having an output circuit, with a regenerative feedback from the output circuit to the input circuit of the transistor amplifier stage, the input circuit of the transistor amplifier stage having a limiter branch therein, includes a double current mirror operatively connected in the input circuit of the transistor amplifier stage and including a first and a second current mirror coupled to one another in a manner that currents supplied thereby are subtracted from one another at a circuit output, the transistors in the second current mirror having a larger emitter surface ratio in comparison with the emitter surface ratio of the transistors in the first current mirror.
A system to analyze the impedance of interference-tolerant proximity sensors. A lock-in amplifier (LIA) is implemented as a resonance-tracking oscillator. The control loop of the amplifier monitors the response of sensor in relation to the output of a local oscillator to adjust the oscillator's frequency to resonance. The nature of the sensor acts as a pre-filter of noise for a synchronous demodulator, which demodulates the sensor's response with the local oscillator's driving signal. The output of the system is a filtered version of this demodulated signal. This system is effective in sensing objects in the presence of electromagnetic noise that is many times stronger than the signal produced by the local oscillator.
An inductive measurement is carried out of the distance between a workpiece (3) and a working head (1), which bears an induction coil (8), through which an alternating current flows and which is part of a resonance circuit whose oscillation frequency is monitored for changes which occur as a consequence of changes in the distance between the workpiece (3) and working head (1). In this case, the working head (1) acts on the workpiece (3) with a material (2) having a dielectric constant greater than 1. The frequency of the alternating current is in the megahertz region or just therebelow. Last but not least, the induction coil is screened from external electric fields in order to avoid the influence of parasitic capacitances.
A new and improved method and apparatus is disclosed for detecting a target location with respect to an inductive tank circuit. A sensing field such as an electromagnetic field is established having an amplitude which changes in value due to the presence of a target in the sensing field. A first energy level is provided to maintain the field at an amplitude. A second energy level is provided to achieve a value for the field within the predetermined amount of time after initiation of the field.
