Abstract: A method of null balancing a hand field-strength meter is described in which the effect of the measurement probe on the balancing is suppressed by short-circuiting the measurement probe by two MOS-FETs connected in series across the probe outputs so that the null balancing can be performed when the field-strength meter is located in the vicinity of a high strength field. In a preferred embodiment of the null balancing circuit for the meter another circuit branch consisting of two other complimentary MOS-FETs connected in series with each other is connected in parallel across the first two MOS-FETs via two resistors R1,R2.

Abstract: A feedback operated DC bridge circuit for monitoring the voltage variations in a voltage divider circuit using a voltage controlled resistance component to reach a null balance across the bridge. Amplification is provided at higher accuracy near the null point when the voltage difference across the bridge is zero. The feedback bridge circuit includes an integrator which directly drives the controlling component to the value of the resistance in an unknown branch to force the null condition. The voltage controlled component (configured as a discrete metal oxide semiconductor device or bipolar junction transistor) and the balancing scheme are suitable for microfabrication and provides noise-rejection enhancement. The interconnected integral feedback of the autonulling DC bridge enables both a neural network for pre-processing sensor input in a spatial domain as well as general analog computation that mimics a first order differential equation in the form of the system state equation.

Abstract: An apparatus for monitoring current through a lamp circuit that uses a series resistance shunt in the circuit with one end connected to a current source and the second end connected to the lamp. The apparatus includes a comparator that is connected across the shunt and has a threshold switching voltage wherein a voltage across the shunt that is larger than the threshold switching voltage will switch the comparator on and a voltage across the shunt that is smaller than the threshold switching voltage will switch the comparator off. A biasing circuit, connected to and controlling the comparator, temperature compensates the threshold switching voltage such that the threshold switching voltage changes proportionally to absolute temperature and controls a sensitivity of the threshold switching voltage to changes in a supply voltage of the circuit. In a preferred embodiment, the shunt is a portion of the printed board trace.

Abstract: A thermal power sensor for providing an output signal that is linearly related to the amount of power derived from a power source over a first range and that is square law related to the amount of power derived from a power source over a second range which may overlap the first range. The apparatus comprises a pair of matched transistors connected in a common emitter configuration. Each of the matched transistors is thermally coupled to a matched resistor so that heat generated in the resistor is transmitted to its respective transistor to cause temperature variations therein. The current through each transistor is a function of the temperature of the transistor. The matched transistors are connected in series with a pair of cascode transistors. The cascode transistors are connected to a first differential amplifier which senses and amplifies the differential voltage which results from any difference in current flow through the matched transistors.

Abstract: A self-contained autonulling bridge circuit based on phase-sensitive deteon of an impedance to be measured is described. The system utilizes a feedback structure to control a variable impedance in order to establish the null of the bridge. The system utilizes a voltage-variable impedance having both resistance and capacitance and provides the phase sensitive relationship in the control means in order to provide highly accurate measurement of an unknown test impedance. The ability to measure small changes in impedance provides particularly useful application to the area of biological sensor impedance measurement or electrochemical impedance measurement using silicon-based devices.

Abstract: A voltage measuring apparatus comprises an optical probe furnished with an electro-optic material whose refractive index is changed in accordance with a voltage developing in a given part of an object and an auxiliary electrode for terminating electric lines of force coming from the given part, a light source for producing light to be inputted to the electro-optic material, a light polarization detector for detecting a polarization state of output light from the electro-optic material, and a power source for applying a variable voltage to the auxiliary electrode. An absolute value of the voltage in the given part can be determined as a specific value of the variable voltage obtained when no change is detected in the polarization state of the output light.

Abstract: A capacitance to voltage conversion circuit for converting changes in capacitance of a capacitive bridge-type probe to voltage includes a detector for detecting changes in an excitation signal across a sensitive arm of the probe due to changes in capacitance of the sensitive arm. A variable gain amplifier having a gain control amplifies the output of the detector. The output of the amplifier is fed to a synchronous detector, and the output of the synchronous detector is fed to a comparator whose other input is fed from a source of reference voltage. An offset circuit provides a predetermined imbalance to the bridge, and a switching circuit are provided for switching the offset circuit in the sensitive arm. Both the synchronous detector and the offset circuit are clocked by a reference oscillator.

Abstract: A true RMS instrument using a multijunction thermal converter with two beaters automatically determines and displays the RMS value of an unknown voltage using two steps or modes. In an AC mode, the unknown voltage is attenuated and balanced in the thermal converter with a DC voltage. DC voltage is stored in digital form in a first latch. In the DC mode, the unknown attenuated voltage is replaced by a chopped DC voltage which is then balanced with the DC voltage obtained in the AC mode. The unknown voltage is determined by decoding the contents of a second lath which controls the chopped DC voltage.

Abstract: A variable resolution system for a potentiometer converts the analog output of the potentiometer to digital steps which are multiplied to provide a number of digital output steps dependent upon the extent of potentiometer movement since last reversal. Upon each reversal, the number of output steps per input step is reduced to provide greater resolution.

Abstract: A differential thermal wattmeter of the type disclosed in U.S. Pat. No. 4,045,734 is modified to remove undesirable in-phase a.c. ripple at the fundamental frequency in the feedback path. This result is achieved by a closed loop system in which the in-phase signal in the feedback path is detected and driven to zero by injecting sufficient signal in opposite polarity into the feedback path to cancel the ripple. The advantages are reduction of error and the ability to use standard, low cost components.

Abstract: An electrical interlock to prevent unauthorized access to potentially hazardous equipment and an associated detection circuit to detect if a safety shield or closure member is open, not securely closed or has been tampered with and to thereupon automatically de-energize the equipment. The detection circuit may comprise a balanced bridge incorporating the electrical interlock into a leg thereof and may also provide a visual or audible indication whenever the bridge is unbalanced thereby indicating an improperly closed safety shield.

Abstract: A security system of the bridge circuit type has in one of its arms a conducting element whose impedance is to be monitored and in its other arms reference and/or compensating elements, for detecting an unbalance of the bridge resulting from a sudden change in the impedance of the conducting element. At least one of the reference elements has a variable impedance. The phase shift of the signal obtained at the output of the bridge circuit is detected, due to the drift of the bridge circuit, with respect to the A.C. supply frequency. The detection signal is then used for compensating the drift by acting on the reference element having a variable impedance in order to bring the bridge circuit back to balanced condition.

Abstract: A substantially non-loading circuit for measuring voltages in a range with relatively high upper limit uses a resistive voltage divider for scaling down these voltages for application to a digital voltmeter capable of measuring voltages in a range with relatively low upper limit. The loading that the input circuit of the resistive potential divider would place on the circuit being measured is reduced by placing the loading of the potential divider input circuit on an electrically adjustable voltage supply, rather than the circuit being measured. The current loading on the circuit being measured is sensed; and the output voltage of this supply is automatically adjusted by feedback to reduce the sensed circuit. In this way, loading of the circuit being measured is reduced, thus avoiding undesirable reduction of the voltage across the circuit owing to its being loaded.

Abstract: A digital alarm system for monitoring a variable process signal utilizing a variable, digitally controlled alarm hysteresis capability. The system includes a means for establishing a preselected count level at which an alarm condition occurs. The preselected count level may be established in a high alarm or a low alarm state depending upon the process signal being monitored. Digital signals representative of the process variable are compared with the preset count level signals and upon a coincidence, an output signal is generated to provide alarm signals and also to reset the preselected count level signal to a second preselected count at a level which is a wide variation from the original preselected level so a relatively large change in the process signal occurs before the system is reset to its original alarm condition.

Abstract: A voltage indicating meter is connected between the outputs of two high impedance operational amplifiers, the first of which receives an input signal to be measured through a range setting resistance dividing network and having a gain which can be set to one of a plurality of different values. A zero control network applies a bias voltage to the inverting input of the second operational amplifier for zeroing the meter. The non-inverting input of the second amplifier can be connected either to the output of the first operational amplifier or to a source of reference potential. When, during operation, the non-inverting input of this amplifier is connected to the source of reference potential, the one terminal of the meter is clamped to the bias level and the other receives a voltage proportional to the voltage of given polarity being measured and the meter needle swings in a given direction.

Abstract: A vacuum fluorescent display has a filament heated below incandescence and phosphor coated anodes. A foraminous charge-control electrostatic lens between the filament and the viewer both controls uniform illumination of the anodes and also comprises part of a contrast-enhancement element. An embodiment of the invention with a linear array of anodes and an analog-to-digital power supply forms a linear scale indicator.

Abstract: A bridge circuit for measuring or use in a temperature-responsive servo-mechanism. A chain of four or alternatively five resistors is connected between power supply rails, an inner two resistors of the chain being shunted by the track of a potentiometer. A balancing potentiometer is connected directly across the supply rails and has its wiper connected to one side of a balance detector through a high value resistor. The signal to be measured is applied between the chain of resistors and the other side of the balance detector. There is a resistive connection from the wiper of the first-mentioned potentiometer and the resistor chain to the end of the high value resistor nearer the detector. The signal to be measured is derived from a resistance-type or thermo-couple temperature sensor. Reference junction compensation for the latter is described.

Abstract: A pressure measuring system which includes a variable reluctance pressure transducer energized from an alternating voltage source, wherein the ratio of the output voltage to the source voltage is proportional to the pressure being sensed. Precision full wave rectifiers convert the source and output voltages to reference and sensing direct voltage signals, respectively. A switching regulator regulates the higher amplitude reference voltage signal to have exactly the same average voltage as the sensing voltage signal. The switching regulator also regulates a constant voltage DC signal from a regulated power supply at the same switching duty cycle as the regulated reference voltage signal, to produce a direct voltage, pressure-sensing signal which is uneffected by voltage fluctuations in the alternating voltage source for the pressure transducer.

Abstract: An apparatus and method for detecting metabolic activity in a medium which includes an electrical circuit suitable for passing electrical current through a medium which contains a suspected metabolic agent. The circuit includes means for generating a reference voltage. When metabolic activity occurs in the medium the voltage drop thereacross changes. To balance the changing voltage developed across the medium with the generated reference voltage, an adjustment of current has to be performed. By monitoring such adjustments, made electrically and automatically, there is a correlation made between those adjustments and the metabolic activity in the medium. Use of this apparatus and method allows large quantities of sample media to be tested for detection of metabolic activity rapidly, accurately and reliably.

Abstract: The output voltages produced by two directional couplers are applied to analog circuitry for generating a voltage that is directly proportional to return loss. An analog meter scale is calibrated to indicate return loss in decibel units and/or voltage standing wave ratio (VSWR) directly.

Abstract: A digital indication for a selectable impedance circuit consisting of a plurality of serially connected impedances and a selector which is connectable to a common junction of any of them is provided by connecting an electric signal source to the end terminals of the circuit to develop a signal between the selector and at least one of the end terminals which is compared with the output of a digital/analog converter, the converter being connected to the output of a digital counter which continues to receive clock pulses until disabled from doing so by a comparison difference within a predetermined tolerance.

Abstract: A device for accurately measuring the quantative value of the real part of complex impedance without the measurement affecting or being affected by the reactive component of that impedance. The device is useful for impedance matching, and especially for tuning antennaes and the like such that the real part of the impedance can be appropriately matched with the source or receiver during tuning. The device operates by comparing the power delivered to the load with the power dissipated in a resistance R when a current proportional to the main line current passes through it. When both power readings are the same, which may be determined by a null indicator, the real part of the load impedance equals the resistance R.

Abstract: A bridge circuit for combination with a variable resistance sensor whose resistance may vary as a function of a sensed variable and also as a function of a parasitic variable such as, for example, temperature. The bridge circuit includes at least one variable resistance which varies as a function of the parasitic parameter and is relatively insensitive to the sensed parameter. The bridge circuit comprises a first leg incorporating the sensor resistor having a tap junction whose voltage varies as a function of the sensed parameter and of the parasitic parameter, a second leg including the parasitic parameter responsive resistance and having a voltage tap whose voltage varies only as a function of the parasitic parameter and a third leg interconnecting the first and second leg voltage taps and having a signal tap whose voltage varies only as a function of the sensed parameter.

Abstract: There is disclosed a motor control circuit that is particularly useful for the control of a damper motor in a heating and ventilating system. The control circuit comprises a bridge circuit having a pair of operational amplifiers with cross connected input terminals. An input signal is provided by input signal circuit means to one of the cross-connecting conductors and a reference signal is provided to the other of the conductors by a reference signal circuit means. The operational amplifiers are provided with feedback circuit means between their output and noninverting terminals to drive the amplifiers into an unstable condition where they function as on and off switches. Dead band means in the form of a load dropping resistor is provided between the input signal circuit and the noninverting terminal of one of the amplifiers.

Abstract: The invention relates to the supervision of a measuring circuit which is connected to a load by way of measuring leads. This load is connected to a generator via supply leads. The load is bridged by a resistor. If one of the four said leads is interrupted, the potential on one of the ends of the resistor changes. As a result, a transistor becomes conductive, which implies an error signal. In a preferred embodiment, two transistors are provided, the first transistor being rendered conductive by a voltage difference. The second transistor is rendered conductive either by a voltage difference or by the fact that the first transistor becomes conductive.