Abstract: Apparatus and associated methods relate to sensing a physical parameter and verifying correct operation of a system used to sense the physical parameter. A sensing device includes four resistive elements configured in a Wheatstone bridge configuration is configured to sense the physical parameter. A biasing network selectively provides first and second biasing conditions to the sensing device. First and second output electrical signals are generated by the sensing device in response to the first and second biasing conditions, respectively, selectively provided to the sensing device. The first and second output electrical signals are each indicative of the parameter value of the physical parameter, but not necessarily equal to one another. A verification module verifies correct operation of the system based on a consistency determination of first and second output electrical signals.

Abstract: A system may include a display driven using display driving circuitry to present an image via pixels. The display driving circuitry may include a sensor core compatible with one or more strain sensing circuits. The same sensor core may be used by a control system of the display to sense a stress applied to a strained region of a display using a current divider sensing circuit and/or a Wheatstone bridge sensing circuit.

Abstract: A three-dimensional integrated circuit includes a first layer including at least one sensing element configured to output at least one temperature-dependent voltage; and a second layer disposed vertically with respect to the first layer and coupled to the first layer by at least one via. The second layer includes: a compare circuit configured to generate at least one intermediate voltage in response to comparing the at least one temperature-dependent voltage to a feedback voltage; a control circuit configured to generate at least one control signal in response to the intermediate voltage; and a switching circuit configured to couple a capacitor coupled to a feedback node to one of a first voltage supply and a second voltage supply in response to the at least one control signal to generate an output signal that is based on a temperature sensed by the sensing element.

Abstract: An electric vehicle may include a board having two deck portions each configured to receive a foot of a rider, and a wheel assembly disposed between the deck portions. A motor assembly may drive the wheel assembly in response to board orientation and rider presence information. A rider detection mechanism may include one or more strain gauges, and may be configured to detect rider presence and rider weight information. A responsiveness of the motor may be automatically adjusted based on the rider weight information.

Abstract: A strain amplification sensor having a first base portion being coupled to a first member to be strain measured, a second base portion being coupled to a second member to be strain measured, and an amplifying lever system pivotally coupled between the first base portion and the second base portion. The amplifying lever system includes attachment locations that induce opposing relative motion resulting in detectable deflection of the amplifying lever system in response to application of strain between the first base portion and the second base portion.

Abstract: A signal compensation unit includes an adjustment section configured to adjust temporal variation characteristics of a detection signal obtained by a bend sensor. The adjustment section includes: a signal amplifier including a positive input terminal, a negative input terminal, and an output terminal, and amplifying the detection signal; and a resistor for adjustment of the temporal variation characteristics disposed between the positive input terminal and the negative input terminal of the signal amplifier.

Abstract: An apparatus for the nondestructive measurement of materials that includes at least two layers of electrical conductors. Within each layer, a meandering primary winding is used to create a magnetic field for interrogating a test material while sense elements or conducting loops within each meander provide a directional measurement of the test material condition. In successive layers extended portions of the meanders are rotated so that the sense elements provide material condition in different orientations without requiring movement of the test circuit or apparatus. Multidirectional permeability measurements are used to assess the stress or torque on a component. These measurements are combined in a manner that removes temperature effects and hysteresis on the property measurements. This can be accomplished through a correction factor that accounts for the temperature dependence.

Abstract: Apparatus and methods for applying stress-induced offset compensation and/or scale factor correction in sensor devices are provided. One sensor device (100, 300, 500, 700) includes an integrated circuit device (110, 310, 510, 710), a transducer (120, 320, 520, 720) coupled to the ASIC device, and a stress sensor (130, 330, 530, 730) coupled to the transducer or the integrated circuit device and configured to measure stress on the sensor device independent of the transducer. Another sensor device (900) includes a transducer, a sensor package (940) enclosing the transducer, and a stress sensor (930) coupled to the sensor device package and configured to measure stress on the sensor device independent of the transducer. A method includes detecting, via a stress sensor, an amount of stress being applied to the sensor device and adjusting, via the stress sensor and independent of the transducer, an output of the sensor device by the detected amount of stress.

Abstract: A methodology for selecting and properly placing foil strain gages on a transducer in a Wheatstone bridge, which provides a more consistent creep response, especially when the transducer temperature is changed. A transducer includes a counterforce subjected to a predetermined physical load that provides tension and compression strains (positive and negative, respectively). The transducer also includes a plurality of strain gage grids that are operatively attached to the counterforce in the tension and compression strain areas of the counterforce and generate electrical signals. The plurality of strain gages are electrically connected in a Wheatstone bridge circuit where their electrical signals due to creep are cancelled.

Abstract: A device includes a structure, a strain sensor and a light curable adhesive. The structure has a structure surface. The light curable adhesive bonds the strain sensor to the structure surface.

Abstract: A mechanical property testing device and method for reliably measuring strain and fatigue characteristics of material specimens is described. An input electrical signal is applied to create an electric field around a first piezoelectric member. The resultant deformation of the first piezoelectric member transfers a force to the specimen being tested which transfers a force to a second piezoelectric member causing deformation. The deformation of the second piezoelectric member generates an output electrical field which is measured. The stress state of the specimen is calculated from fundamental material constants and the measured output electrical field.

Abstract: A correcting circuit includes a correction current synthesizer synthesizing a correction current based on an output signal of a sensor, a current adjuster adjusting a determining current which corresponds to a correction amount based on the correction current, and a correction voltage generator generating a correction voltage for correcting a voltage signal based on the determining current, so as to correct an output characteristic of a voltage signal output in correspondence to the output signal of the sensor.

Abstract: Apparatus and methods for applying stress-induced offset compensation and/or scale factor correction in sensor devices are provided. One sensor device (100, 300, 500, 700) includes an integrated circuit device (110, 310, 510, 710), a transducer (120, 320, 520, 720) coupled to the ASIC device, and a stress sensor (130, 330, 530, 730) coupled to the transducer or the integrated circuit device and configured to measure stress on the sensor device independent of the transducer. Another sensor device (900) includes a transducer, a sensor package (940) enclosing the transducer, and a stress sensor (930) coupled to the sensor device package and configured to measure stress on the sensor device independent of the transducer. A method includes detecting, via a stress sensor, an amount of stress being applied to the sensor device and adjusting, via the stress sensor and independent of the transducer, an output of the sensor device by the detected amount of stress.

Abstract: A rail stress monitoring system is disclosed. This system includes a sensor module that further includes a sensing device that is adapted to be mountable directly on a length of rail. The sensing device further includes a generally flat metal shim and at least one, and typically two or more, sensors mounted on one side of the shim. The sensors are typically strain gauges, which are mounted on the shim in a specific, predetermined configuration. At least one data acquisition module is in electrical communication with the sensing device and a data processing module receives and processes information gathered by data acquisition module.

Abstract: A mechanical property testing device and method for reliably measuring strain and fatigue characteristics of material specimens is described. An input electrical signal is applied to create an electric field around a first piezoelectric member. The resultant deformation of the first piezoelectric member transfers a force to the specimen being tested which transfers a force to a second piezoelectric member causing deformation. The deformation of the second piezoelectric member generates an output electrical field which is measured. The stress state of the specimen is calculated from fundamental material constants and the measured output electrical field.

Abstract: The output signal from a measuring transducer in a force-measuring device is processed by filtering a measuring signal (ms), representing a load that is acting on the transducer, to suppress interfering signal portions caused by extraneous influences including mechanical disturbances, or changes of the load. The measuring signal (msE) passes through a first delay element (141A) to a measurement value unit (145) which holds the value of the currently received measuring signal (msE), a mean value based on the most recent values of the measuring signal, or an expected value (msE) based on the most recent values of the measuring signal. The measuring signal (msE) is monitored for signal disturbances using a first detector module (151). After detection, a switching means (142) is actuated and the output signal (msX) of the measurement value unit is processed further, if applicable, and sent to the output end of the device, instead of the currently received measuring signal (msE).

Abstract: A structure includes a structure surface and a protective cover. The protective cover includes a circuit having a component, a moisture detector, and a radio frequency transmitter. The component is adhesively connected to the structure surface with an adhesive connection. The moisture detector is positioned to provide information about moisture in the protective cover. The circuit is for providing data derived from the component and from the moisture detector to the radio frequency transmitter for external transmission. The component may be a strain sensor. The moisture detector may be a capacitor. A moisture barrier may also be provided.

Abstract: A deformation detection sensor including: a piezoelectric element which generates an output signal due to a deformation; a reference signal input device which inputs a reference signal of a predetermined cycle to the piezoelectric element; a first signal extraction device which extracts a first output signal due to the deformation of the piezoelectric element out of an output signal from the piezoelectric element; a second signal extraction device which extracts a second output signal due to the reference signal out of the output signal from the piezoelectric element; a first evaluation device which evaluates the first output signal extracted by the first signal extraction device; and a second evaluation device which evaluates the second output signal extracted by the second signal extraction device.

Abstract: A method and system for reducing operational shock sensitivity of a MEMS device includes a closed-loop control circuit for controlling the MEMS device and a shock detector for detecting a shock experienced by the MEMS device. The closed-loop control circuit includes a movable MEMS structure, a detector for sensing a position of the MEMS structure and for providing a first feedback signal related to the sensed position, and a processor for receiving the first feedback signal and for providing a control signal used to control the MEMS device. The shock detector, which according to a preferred embodiment is the MEMS structure itself, is used for detecting the shock experienced by the MEMS device and for generating a second feedback signal, which is used to alter the control signal such that a response of the closed-loop control circuit to the shock is minimized.

Abstract: A strain sensing apparatus for use in the presence of thermal gradients has a strain gauge and resistance temperature gauge in a planar assembly bonded to, deposited on or diffused or implanted in a substrate surface. The apparatus can sense strain and temperature independently and can be used alone or with a plurality of installations in strain gauge based transducers or experimental stress analysis. The output from the temperature gauge can be used accurately to compensate for unwanted thermal effects in the strain gauge and to measure temperature at the strain gauge site.

Abstract: A temperature compensated strain gauge assembly comprises a strain gauge (10) having two or more resistor or piezoresistors (Rb) in half bridge or full bridge configuration and one or more temperatures compensating resistors or piezoresistors (Rc) connected in series with the bridge resistors or piezoresistors. The resistance of the temperature compensating resistor(s) or piezoresistor(s) is such that, as temperature changes, the compensating resistor(s) or piezoresistor(s) compensates for a change in span of the strain gauge so that, for a given load applied to the substrate, the span of the strain gauge will remain constant or substantially constant and compensate(s) the null shift of the strain gauge when the bridge resistors or piezoresistors are such as to provide a known offset at a given temperature.

Abstract: A self-compensated strain gage sensor having a temperature co-efficient of resistance (TCR) of essentially zero comprised of a wide band semiconductor and a compensating metal functioning as serial resistors. Based on the resistivity of the semiconductor and the metal and the temperature range in which the sensor will operate the dimensions of the semiconductor and the metal are determined to provide a zero TCR.

Abstract: A screwer test bench includes a coupling designed for connection with the head of a screwer and connected to a controlled braking unit and a sensor unit for detection of mechanical magnitudes transmitted between the coupling and the braking unit. The braking unit includes a thin cap constrained to said coupling at least in the direction of rotation and arranged between a first pressure surface thrust axially against the cap by an actuator and a second fixed opposition surface.

Abstract: The invention creates a micromechanical component, in particular a pressure sensor, comprising: a substrate (2) that has a membrane region (10) and a surrounding region of the membrane region (10); at least one measuring resistance (4a, 4b; 41, 42) provided in the membrane region (10) and modifiable by deformation of the membrane region (10); a corresponding evaluation circuit (50) provided in the surrounding region, an interference effect on the measuring resistance (4a, 4b; 41, 42) being producible by way of a deformation of parts, in particular conductor paths, of the evaluation circuit (50) relative to the substrate (2); and at least one patch (60; 70, 70′) provided in the surrounding region and/or in the membrane region (10) and made of a material such that by way of a deformation of the patch or patches (60) relative to the substrate (2), an analog interference effect can be generated in such a way that the interference effect acting on the measuring resistance (4a, 4b; 41, 42) can be compensated

Abstract: A method and system for calibrating a sensor is disclosed The method and system include receiving data relating to a plurality of temperature parameters and providing polynomial compensation of a temperature coefficient (TC). When providing polynomial compensation of the temperature coefficient, the method and system further include providing a first output and adding a second value to the first output. The first output is a distal temperature multiplied by a first value.

Abstract: A method and apparatus for pre-straining a bolt-on strain sensor. The pre-strain is preferably adjusted by inserting a strain adjusting tool through strain adjusting holes in the sensor and the structural member. The portion of the tool engaging the sensor is preferably offset from the portion of the tool engaging the hole in the support structure to provide a camming function. After the strain has been adjusted to a desired value, a bolt adjacent the strain adjusting hold of the sensor is tightened to fixedly secure the sensor to the support structure and maintain the preadjust strain at the desired value.

Abstract: A capacitive transducer (10) which provides an output voltage in response to the application of a mechanical stimulus such as pressure or acceleration includes a signal conditioning integrated circuit (12) to which are connected a variable capacitor (C.sub.VAR), a reference capacitor (C.sub.REF), a linear correction capacitor (C.sub.LIN) as well as an integrating capacitor (C.sub.INT) and associated filtering components. The linear correction capacitor (C.sub.LIN) is used to offset a fixed parasitic charge associated with the variable capacitor. Any net error charge appearing on a detect, common node (pin 4) between the variable capacitor and the reference capacitor is cancelled out by means of an analog feedback network (22). In a modified embodiment a thermal compensation network (40) allows for correction for thermal error at a second temperature without having any affect at a first temperature.

Abstract: An apparatus for trimming gain of an accelerometer to a desired gain value G.sub.t. The apparatus includes an accelerometer for providing an electric signal indicative of experienced acceleration with an intrinsic gain G.sub.s. An amplifier amplifies the accelerometer signal with an amplification value responsive to the accelerometer's intrinsic gain G.sub.s so as to have the desired gain value G.sub.t.

Abstract: An analog input apparatus comprises bridge measuring devices 11 and 31 connected to a bipolar voltage power supply 5, analog multiplexers 18, 19, 38, and 39 responsive to an output level of an oscillator 4B for switching a polarity and outputting two outputs of each of the bridge measuring devices 11 and 31, amplifiers 12 and 32 for amplifying bipolar outputs provided through the analog multiplexers 18, 19, 38, and 39, and an analog-to-digital converter 2 for converting outputs of the amplifiers 12 and 32 into digital form and outputting the resultant digital values.

Abstract: An analog input method comprises the steps of correcting a measured value with the digital value output when voltage at either middle point of a bridge circuit is fed into both input terminals of a differential analog amplifier or feeding two middle-point voltages of a bridge circuit into input terminal of an analog amplifier in order and providing a measured value based on the difference between the digital values output from the analog amplifier.

Abstract: A circuit for generating a linear current proportional to the displacement of the movable member of a transducer receives an undetermined supply voltage from a monitoring circuit which has a relatively high internal resistance. The circuit is provided with two parallel current paths with one path including a resistive potentiometer strip and other path including a transistor and resistor connected in series. The movable member of the transducer has an electrical contact member attached thereto with the contact member having one end making contact with the resistive potentiometer strip and with the other end thereof making contact with a conductive strip which is connected to the gate of the transistor so that the current drawn by the circuit will be linearly related to the movement of the movable member.

Abstract: A sensing apparatus for sensing at least two physical quantities is disclosed. The sensing apparatus includes a first transducer that provides a first output signal proportional to a first measured quantity represented and a second transducer that provides a second output signal proportional to a second measured quantity. An excitation regulator device is connected to the first transducer and the second transducer. The excitation regulator device provides an excitation signal to the second transducer so that the second transducer output signal is referenced to the first transducer output signal in order to obtain a resultant output signal which is a combination of the first and second output signals.

Abstract: A clamp-on structural strain-gage sensor that is mounted to dynamic load-bearing structures, such as sucker-rod type oil well pumps, to produce an electrical output proportional to the deflection of such structures. The apparatus uniquely includes an active electronic temperature correcting circuit to provide compensation for the erratic effects caused by uneven thermal heating of the load-bearing structure.

Abstract: An analog input apparatus comprises bridge measuring devices 11 and 31 connected to a bipolar voltage power supply 5, analog multiplexers 18, 19, 38, and 39 responsive to an output level of an oscillator 4B for switching a polarity and outputting two outputs of each of the bridge measuring devices 11 and 31, amplifiers 12 and 32 for amplifying bipolar outputs provided through the analog multiplexers 18, 19, 38, and 39, and an analog-to-digital converter 2 for converting outputs of the amplifiers 12 and 32 into digital form and outputting the resultant digital values.

Abstract: A circuit for measuring variations in the capacitance of a variable capacr forming part of a sensor includes an oscillator which generates an alternating signal which is supplied to two branches of a detection bridge. The first branch includes the variable capacitor connected in series with a variable capacitance diode. The second branch includes a capacitor connected in series with a variable capacitance diode. A differential stage has each of its in puts connected to the common point of a respective one of the branches. Synchronous demodulation means connected to the oscillator, are connected to the output of the differential stage for delivering a DC unbalance voltage Ve which is injected by a feedback line to the common point of the first branch, thereby continuously balancing the detection bridge.

Abstract: Disclosed is a method of compensating any of a plurality of different pressure transducers for their characteristic pressure sensitivity, zero pressure offset, and self-heating error. The method comprises selecting a gain resistor that adjusts the gain of an output signal of the pressure transducer in use so that the pressure transducer appears as an ideal pressure transducer to a pressure monitor. The self-heating error is compensated by measuring an initial bridge voltage that drives the transducer and an initial output signal of the pressure transducer when the transducer is first energized. After a period of time a second bridge voltage and a second output signal are determined. The self-heating error is determined as a function of the difference between the initial and second values. The zero pressure offset is compensated by determining the output signal of the pressure transducer at zero gauge pressure after the pressure has been compensated for the self-heating error.

Abstract: A load measuring device has a plurality of links 2 arranged in a chain to which a load to be measured is applied, respective sensing elements G disposed on two or more links for detecting the strain on the links 2 and giving output signals dependent on the strains, and electronic processing circuitry including a microcomputer system 12 to process the signals and to compute a value for the applied load.

Abstract: A heater control device for an air-fuel ratio sensor which comprises: an air-fuel ratio sensor comprising a sensor element which detects an air-fuel ratio state of exhaust gas of an engine, and a heater which heats the sensor elements; a heater current flow control means for controlling a value of a resistance of the heater to be a target resistance value; a harness having a couple of couplers at both ends thereof which connects between the air-fuel ratio sensor and the heater current flow control means; and a current detecting resistance which is incorporated in the coupler on the air-fuel ratio sensor side, or provided adjacent to said coupler on the air-fuel ratio sensor side, and which is connected to the heater in series and detects current of the heater.

Abstract: A device used in an apparatus, such as weigher, pressure gauge or the like, for essentially measuring a force, which utilizes a flexural member of elastic material for detecting the force by converting its deflection or strain caused by application of the force into an electric signal, and adapted to compensate for measurement error caused by a time-dependent change in the detection output as a result of creep and/or stress reluxation of the flexural member by removing error components by an electric circuit constructed in accordance with a principle of digital filter.

Abstract: A device and method for trimming diffused or implanted resistors incorporated within a silicon sensor. Current pulses are applied to cause the migration of aluminum contacts in silicon, resulting in controllable incremental reductions in resistor value. The resistors are symmetrically positioned within a Wheatstone bridge to correct offset voltage and sensitvity erros that result from manufacturing tolerances.

Abstract: A method of error compensation for transducers having non-linear characteristics is shown. A computer-supported measuring circuit is used. In a first factory alignment, the output characteristic of the transducer is set so that it can be linearized by the computer using a power function. The appropriate exponent of the power function is stored. At the place of use, at least three calibration measurements are performed with the installed transducer using defined calibration measured values substantially spanning the measuring range of the transducer equidistantly. The power function is solved with the calibration measuring results and the stored exponent, so that the constants not yet known can be calculated. During every following service measurement, the actual measuring result is put into the now solved power function. The result of the equation is then outputted as the error-compensated measuring result.

Abstract: Methods and apparatus by which a transducer is employed to create a digital signal representing numerically the value of a changeable physical parameter. The signal from the transducer is subject to large and unpredictable amounts of offset due to either or both (i) manufacturing tolerance departures from the desired target of creating a zero output signal value when the sensed parameter is zero and (ii) changes in offset due to changes in one or more physical conditions (other than the sensed parameter) to which the transducer and its associated electrical components are subjected. A bistate device is associated with the transducer and controlled so as (a) to first apply substitutionally to the transducer a known, and preferably zero, value of the parameter--with the output signal value being stored so as to represent the then-existing offset, and then (b) to apply the changeable physical parameter to the transducer.

Abstract: A self-calibrating sensor system is disclosed wherein a processing circuit, normally including an amplifier, receives the output of at least one sensor to develop a processed sensor signal. To compensate for errors (gain error, etc.) in the processing circuit, the preferred embodiment includes a microprocessor which senses certain signals developed by the processing circuit, computes correction factors based on the sensed signals, and then modifies the processed sensor signal so as to substantially eliminate the effect of the errors.

Abstract: A resistance-gauge force transducer comprises a resilient bar having one end adapted to be fixed to a stationary support and the other end subjected to the force to be measured. The bar carries two pairs of resistance gauges symmetrically disposed on both sides of the center of gravity of the bar. The direction of the lines of current of a gauge of one pair is parallel to the bar axis and perpendicular to that of the other gauge of the same pair. The gauges are electrically connected together so as to form a wheatstone bridge delivering a signal which is a function of the force applied to the end of the bar. The two gauges of one pair are adjacent and connected to each other in the wheatstone bridge. This arrangement renders the force transducer insensitive to thermal variations.

Abstract: A force transducer comprises a resilient bar (1) which carries a measuring bridge formed by resistance gages (R.sub.1, . . . R.sub.4). One end of the bar is attached to a stationary support (2) and the other end is subjected to a force (P) to be measured. A method for ensuring that the signal delivered by the measuring bridge is proportional to the applied force and insensitive to parasitic couples consists in determining the initial characteristics of the transducer, in computing the relative errors arising from a displacement of the force (P) applied as a function of the angle made between the resistance gages (R.sub.1, . . . R.sub.4) and the longitudinal direction (O.sub.x) of the bar (1) and in cancelling these errors by making changes in one or a number of gages in order to modify the angle aforesaid.

Abstract: In the case of sensors having a characteristic for which the offset in the quiescent condition has a first temperature coefficient and the slope of the characteristic has a second temperature coefficient, while the quotient of the offset and slope coefficients is approximately constant, a point can be determined in which the characteristics for different temperatures (T) intercept. A temperature corrected measurement value can be determined, preferably with a microcomputer, from the sensor signal, the coordinates of the above-described intersection point, the sensor temperature and the temperature coefficient either of the offset or of the slope.

Abstract: A method and apparatus for precisely controlling plastic strain rate during plastic deformation testing of a solid material such as a metal or plastic are described in which the effects of elastic strain rates associated with the specimens and machines used for such testing are eliminated by applying corrections proportional to the load on the specimen. Thus strain rate sensitivity, unaffected by the machine or specimen modulus can be measured. Strain rate sensitivity can be used to measure the activation volume of the specimen which may be used for quality control of material processing and/or manufactured articles.

Abstract: A transducer unit comprised of a pair of transducers coupled together in a manner such that the offsets, drifts and the like of the circuit elements of one transducer are opposed by and cancelled out by the circuit elements of the other transducer. The transducers can be in the form of Wheatstone bridges and each of the branches of the bridge contains a circuit element of each transducer, respectively, the circuit elements of the branches of the transducer unit being in opposition to each other so as to cancel out the effects due to temperature, acceleration, aging and the like.

Abstract: A miniature, solid state, cantilever beam accelerometer is constructed with an arrangement of strain sensing elements which provides for simpler temperature compensation, dual-axis acceleration measurement, and the capability of correcting for nonlinearity in a strain sensing element. Temperature compensation is facilitated by locating two strain sensing elements on the cantilever beam and two on the main body of the accelerometer and connecting the four elements in a Wheatstone bridge. Instead of a single bridge, two half bridges may be formed to allow for independent adjustment of each side of the Wheatstone bridge. Independent adjustment is also possible by using two full bridges with all strain sensing elements oriented in the same direction. If the elements of one bridge are oriented in an orthogonal direction, the accelerometer is capable of measuring both on-axis and off-axis accelerations.

Abstract: A force or fluid pressure transducer comprises two plate-like crystals. The force is applied to the first of the two crystals in a direction generally along the crystal faces by two seatings situated at opposing edges of the crystal.An oscillating portion of this first crystal changes its frequency by an amount which is a very accurate measure of the force, providing the ambient temperature of the instrument remains constant.The present invention resides in a second crystal secured to the first crystal at particular force insensitive points, there being very small spacing between the two crystals. The second crystal sustains a negligibly small amount of the force and hence a similar oscillating portion of this second crystal undergoes negligibly small frequency change.Means are provided for adjusting the steady-state temperature behavior of one crystal with respect to that of the other in order to remove residual errors.