Showing papers on "Capacitive sensing published in 1968"

Capacitive moisture control system having a peak detector

Abstract: A meter for measuring moisture in soil electronically uses two probes spaced apart with soil between the probes. The probes may be insulated plates of metal or flat insulated cable made of a plurality of conductors. The circuit has an ultrasonic oscillator which transmits a signal to the probes, which function as a variable capacitor depending upon moisture content of the soil. An integrated-circuit peak detector provides a positive DC voltage proportional to input peak voltage, and its output is measured by a microammeter which thus measures moisture. The output of the detector may be used to control an irrigation valve. Several probes and valves may be used in a system. The soil may be contained in a plastic bag and the electrodes applied to opposite sides of the bag.

Graphical input tablet

Abstract: An a-c potential field is established on an electrographic tablet. A stylus that may be used to write upon the tablet comprises a capacitive pickup to provide a potential representative of the stylus position. The potential field is alternately switched at a rapid rate between vertical equipotentials and horizontal equipotentials in synchronism with output analog switches coupled to the stylus to provide an X analog signal output and a Y analog signal output representative of the horizontal and vertical coordinates, respectively, of the stylus tip above the tablet.

Protective rf attenuator plug for wire-bridge detonators

Abstract: THE PLUG PORTION OF A WIRE-BRIDGE DETONATOR IS REPLACED WITH A FILTER OF THE SAME PHYSICAL SHAPE AND SIZE. THE INPUT CONDUCTORS FOR THE BRIDGE WIRE ARE EACH SURROUNDED BY A SERIES OF CLOSELY SPACED FERRITE BEADS. A CONDUCTIVE SHIELD PLATE IS PROVIDED BETWEEN THE CONDUCTORS FROM WHICH THE FERRITE BEADS ARE INSULATED BY A STRIP OF CERAMIC MATERIAL ON EACH SIDE OF THE SHIELD PLATE. THE PLUG IS PROVIDED WITH END SHIELDS OF CONDUCTING MATEIRAL AND AN OUTER SHIELD CASING WHICH MAY BE OF STEEL OR OTHER CONDUCTING MATERIAL. THE FERRITE BEADS AND THE CERAMIC STRIPS PROVIDE THE INDUCTIVE AND CAPACITIVE ELEMENTS OF AN RF FILTER OR ATTENUATOR ON THE INPUT CONDUCTORS WHICH OPERATES TO ABSORB STRAY RADIATED ELECTROMAGNETIC ENERGY THAT MIGHT BE PICKED UP BY THESE CONDUCTORS, AND PREVENTS THIS ENERGY FROM PASSING THROUGH TO THE BRIDGE WIRE WHICH MIGHT THUS BE PREMATURELY FIRED THEREBY.

High Impedance Langmuir Probes

Abstract: The operating characteristics and limitations of high impedance resistive probes are discussed A new high impedance probe employing capacitive coupling to detect plasma floating potential is described The advantages of capacitive coupling for increasing the input impedance, reducing the size, and broadening the bandwidth are illustrated A typical measurement is described which illustrates some of the advantages of the capacitive coupled probe for measurements of plasma properties in a toroidal octupole

Capacitive displacement transducers with high accuracy and resolution

Abstract: Capacitive displacement transducers can be a particularly accurate and sensitive means of measuring displacement over a wide range They are equivalent to an almost perfect potential divider and when used with inductive ratio arms accuracies to 1 in 106 can be achieved Resolution of better than 1 in 107 is possible and apart from environmental and structural stability a displacement of less than 40 A can be observed

Inductive-capacitive probe in machine for handling sheetlike material

Abstract: Machine for handling sheetlike material, such as a printing press and a sheet feeder therefor, having a combined inductivecapacitive probe for discriminating among the presence of a single thickness of the sheetlike material, the absence of the material, and the presence of excessively thick sheetlike material, such as two or more superimposed sheets, or for determining the moisture content of the sheetlike material. The probe is substantially insensitive to machine vibrations.

Sensing probe and control for press inker embodying same

Abstract: Sensing probe for capacitively sensing the thickness of an ink film being transferred by a printing press inker. The probe has an inductive probe element which is insensitive to the ink film and which offsets changes in the probe''s capacitive response due to machine vibrations, so that the overall response of the probe is substantially insensitive to such vibrations. The probe is part of a control for automatically regulating the rate at which ink is being transferred by the inker.

Capacitive filter for suppression of spurious electrical radiation

Abstract: A capacitive filter arrangement coupled to the voltage supply circuit of an electrical energy generator to reduce undesired radiation of energy to acceptable levels in accordance with Federal Communications Commission specifications and requirements for such generators when employed in certain electronic equipment. Elimination of corona discharge at predetermined levels of alternating current and no breakdown of insulation material at predetermined levels of direct current are other characteristics of the structure of the invention.

Variable Gap Capacitive Detector for the Measurement of Ultrasonic Displacement Amplitudes in Solids

Abstract: A variable gap capacitive detector has been developed for displacement amplitude measurements of longitudinal ultrasonic waves in the frequency range 5 to 100 MHz. The gap spacing is controlled by differential gas pressure. With this device it is possible to maintain a constant detector capacitance for measurements of the temperature dependence of the third order elastic constants. This improves the precision of the measurements considerably.

Moving formant band-pass amplifier for an electronic musical instrument

Abstract: A circuit for achieving the moving or changing formant effect in an electronic musical instrument such as an electric organ. The circuit employs a band-pass amplifier with parallel T resistivecapacitive feedback circuits in which an FET (Field Effect Transistor) is employed as a variable resistance to cut in, by degrees, one of the T feedback circuits. The effective resistance of the FET and thus the band-pass of the amplifier are varied by a capacitive and resistive timing circuit that is controlled via a keying circuit from one or more keys or other player-operated controls, such as the manual keys of an electric organ.

Multiple Reflections from RC Loading of Pulse-Signal Transmission Lines

Abstract: —An analysis is made with equations developed for the capacitive effect of RC loading with multiple reflections on pulse-signal transmission lines. The capacitive hold waveshape and hold time are described and compared with experimental results. Isolating the capacitive effect from the purely resistive case is accomplished so that this effect can be used to modify existing solutions. The analysis results show that a significant capacitive hold time occurs before the wave approaches its final value with oscillations occurring about the initial voltage value. The number of cycles of oscillation are equal to the number of times the wave has been reflected, and the amplitude of oscillation increases with each cycle. These effects are independent of transmission line length. Results are applicable for any system with RC loading and transmission-line effects and, in particular, for high-speed pulse systems. The mathematical results can either be directly applied in reflection analysis or the relative capacitive hold-time results can be added as a corrective factor.

A New Transistor Square-Wave Generator Using Two Regenerative Switches

Abstract: The operation and performance of a new type of circuit for square-wave generation is presented. The circuit is based on the application of two identical regenerative switches using complementary transistors, the operation of which is controlled by a single timing capacitor. Rise and fall times of the output pulses can be made to depend almost entirely on the switching speed of the transistors, and are independent of the values of the elements used in the timing network. The frequency of oscillation can be varied continuously or in steps over a wide range of frequencies by changing one parameter only. With silicon planar transistors used in the regenerative switches, the temperature stability is quite satisfactory, but a simple method for further increase in temperature stability is also discussed. The capacitive (or resistive) loading of the output terminals does not affect the frequency of oscillation. These features make the circuit described very useful in many applications, and particularly in the design of wide-range square-wave generators. An experimental model of the circuit covering the frequency range from 1 Hz to 10 MHz has been built and some results of measurements are presented.

Position transducer using a sweeping field null

Abstract: THE POSITION OF A CAPACITIVE PROBE ON A WRITING TABLET IS CONVERTED INTO DIGITAL AND ANALOGUE SIGNALED BY DETECTING THE TIME AT WHICH A VOLTAGE NULL PASSES THE CAPACITIVE PROBE. A VOLTAGE NULL IS SWEPT ALONG ONE DIMENSION OF THE WRITING TABLET BY APPLYING A PAIR OF EQUAL FREQUENCY OUT-OF-PHASE SIGNALS, WHICH ARE AMPLITUDE MODULATED TO PROVIDE EQUAL RATES OF INCREASE AND DECREASE, RESPECTIVELY, TO THE OPPOSITE ENDS OF A RESISTOR PLACED ALONG THE DIMENSION TO BE MEASURED. THE NULL MOVES LINEARLY ACROSS THE TABLET ALONG THE DIMENSION TO BE MEASURED. THE OUTPUT FROM THE CAPACITIVE PROBE IS A WAVEFORM HAVING AN ENVELOPE WHICH REDUCES TO A NULL AT ONE POINT DURING EACH SWEEPING PERIOD. THE TIME DIFFERENCE BETWEEN THE START OF THE SWEEP AND THE OCCURRENCE OF THE NULL IS A MEASURE OF THE POSITION OF THE CAPACITIVE PROBE ALONG THE DIMENSION TO BE MEASURED. TWO DIMENSIONAL MEASUREMENTS CAN BE ACCOMPLISHED BY SWEEPING THE NULL ALONG THE SURFACE IN A PAIR OF ORTHOGONAL DIRECTIONS, USING EITHER A TIME MUL- TIPLEXING TECHNIQUE, WHEREIN THE NULL IS SWEPT ALONG A SINGLE DIMENSION AT A TIME, OR A FREQUENCY MULTIPLEXING TECHNIQUE, WHEREIN IN CARRIER FREQUENCIES USED TO SWEEP THE NULL ALONG THE ORTHOGONAL DIMENSIONS ARE DIFFERENT FREQUENCIES.

Diaphragms in evanescent waveguides

Abstract: Three diaphragms are considered (capacitive, inductive and tuned window) on a storage-energy basis to determine whether there is any change in the behaviour of these in evanescent guides. It is found that all three are inductive when a guide is operated below the H10 cutoff.

Measurement of surface impedance at microwave frequencies

Abstract: A technique for measuring the surface impedance of a plane stratified media at microwave frequencies is given, and preliminary tests are made for a variety of situations ranging from capacitive impedances to surfaces, which display a purely inductive reactance. The technique utilises a modulated scatterer to measure the elliptically polarised electric field of a TM wave propagation over the surface.

Toy having capacitance switch

Abstract: A SELF-PROPELLED MOTORIZED TOY WHOSE MOVEMENT IS CONTROLLED BY THE DISTANCE BETWEEN IT AND ANOTHER OBJECT, SUCH AS A HUMAN OPERATOR. A TRANSISTOR OSCILLATOR, RESONANT TANK CIRCUIT, CAPACITIVE DEVICE WHOSE CAPACITANCE IS DETERMINED BY THE DISTANCE BETWEEN IT AND THE OBJECT CONNECTED TO THE RESONANT TANK CIRCUIT, AND A TRANSISTORIZED AMPLIFIER ARE CONNECTED TOGETHER IN SUCH A MANNER THAT THE INCREASE OR DECREASE IN CAPACITANCE OF THE CAPACITIVE DEVICE CAUSES A DECREASE OR INCREASE IN THE INPUT SIGNAL APPLIED TO THE AMLIFIER. THE AMPLIFIER IS CONNECTED TO A RELAY SWITCH WHICH IN A FIRST STATE DIRECTS CURRENT FROM A POWER SOURCE TO A MOTOR WHICH OPERATES TO MOVE THE TOY, AND IN A SECOND STATE, DIRECTS CURRENT TO OTHER MEANS WHICH OPERATE OTHER MOVEMENTS OF OTHER PARTS OF THE TOY, SUCH AS FLAPS AND WHISTLES.

A 5-MHz switching multivibrator using a complementary pair of transistors

Abstract: The principle of operation of a novel free-running transistor multivibrator is presented. The circuit is based on the application of a complementary switch, the operation of which is controlled by a single timing network. This circuit provides a suitable means of generating rectangular pulses having rise- and fall-times in the nanosecond range.The circuit exhibits some other useful features which include excellent thermal stability and considerable loading capabilities for both resistive and capacitive loads, and less dependence on power supply variations.The experimental model which was built to verify the design operated properly in the frequency range extending from very low frequencies t frequencies over 5 MHz when only the timing capacitor was changed.

Directional displacement capacitive pickup

Abstract: There is disclosed herein a noncontact proximity-sensitive transducer having improved directional properties formed of an elongated rodlike pickup adapted to provide a distance-sensitive variable capacitance and an annular shielding member fitted onto the end of the pickup. The shielding member includes a conducting plane electrically isolated from the pickup, and maintained at the same electrical potential as the object under inspection. The capacity variation serves as a frequency control element to modulate the output in a high frequency oscillator in accordance with the distance variations being measured.

Synchronization bandwidth of capacitive transverse-field electrooptic modulators

Abstract: Expressions are given that can be used to calculate the synchronization bandwidth of center-fed and end-fed, capacitive electrooptic modulators that employ a modulation field transverse to the direction of optical beam propagation.

Theoretical effects of overlap capacitance upon MOS inverter output

Abstract: Gate overlap and capacitive feedthrough in digital circuits can cause performance degradation. Effects of overlap on a basic MOSFET inverter are considered. An example shows that the inverter output can be reduced significantly due to capacitive coupling.

Touch responsive control circuit

Abstract: A miniaturized solid state, touch responsive circuit wherein a touchplate connected to a regenerative feedback network of a transistor amplifier is operative when touched to supply sufficient capacitive impedance in the feedback network to dispose the circuit in an oscillatory condition. In a preferred form of the invention, an electrical detection circuit is connected to the amplifier and feedback network to respond to the touch induced signal oscillations and provide a rectified control signal for actuating a load switch or the like. Also a hold circuit is provided for sustaining the oscillatory condition of the amplifier circuit automatically after being momentarily actuated by touch, and wherein a second touch plate is provided for terminating this sustained condition again in response to touch.