Glossary of Terms

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Acceleration Sensitivity: On a pressure or force transducer, the undesirable output caused by acceleration (shock or vibration).

Acceleration Compensation: A method used to reduce acceleration sensitivity in pressure transducers. This compensation consists of a tuned acceleration system connected in series, and with opposite polarity, to the pressure measuring system.

Antistrain: Patented Kistler design for pressure transducers which provides mechanical isolation between the mounting thread and the measuring element thereby minimizing mounting torque sensitivity.

Bar: A metric unit of pressure measurement equivalent to 14.503 ... psi.

Bias Voltage: DC (no load or quiescent) output level of a low impedance transducer powered by constant current excitation.

Charge Amplifier: Electronic unit which utilizes a high-gain voltage amplifier with negative, capacitive feedback for converting a charge from a piezoelectric transducer into a low impedance output voltage.

Charge Output: Output in picoCoulombs (pC) from a piezoelectric transducer without a built-in charge-to-voltage converter (see High Impedance)

Circuit Integrity indication: A quick-look reference on couplers or dual mode charge amplifier for identifying whether a low impedance system has the proper bias voltage. Analog meters and multi-color LEDs are the most commonly used indicators.

Constant Current Excitation: Method of powering low impedance transducers to insure minimal sensitivity variation over a wide voltage range.

Coupler: Electronic unit which supplies constant current excitation to low impedance transducers and decouples the subsequent bias voltage.

Cross Talk: Another term for cross axis or transverse sensitivity; used on Kistler multi-component force transducers to describe the output on one axis caused by inputs on the others.

Drift: An undesirable change in output signal, over time, which is not a function of the measurand.

Dual Mode: Refers to a charge amplifier which can be used either with high impedance, charge output or with low impedance, voltage output transducers.

Gage Factor: In piezoresistive transducers, refers to the measure of relative resistance change for a given relative change in length or strain.

Ground Isolation: The electrical resistance between the signal return/common and mounting ground of a transducer, or between an electrical connector shield and power ground of a charge amplifier/coupler.

High Impedance: Another term for a piezoelectric transducer with charge output (i.e. pC/mechanical unit),

Hysteresis: The maximum difference in output, at any measurand value within the specified range when the value is approached first with increasing and then decreasing measurand.*

Impedance Converter: A miniature electronic unit with MOSFET input and Bipolar output for converting high impedance, charge outputs (from a transducer) into low impedance, voltage outputs. Impedance converters can be built into the transducer (see Low Impedance) or can be used externally for special applications.

Insulation Resistance: The leakage resistance of a high impedance transducer, cable or charge amplifier measured between the signal lead and connector ground.

K-BEAM®: Kistler's solid-state, variable capacitance based line of accelerometers which are suitable for measuring low frequencies or even steady state conditions.

K-SHEAR®: Newest member of Kistler's accelerometer family. Low impedance accelerometer which utilizes a shear quartz sensing element.

Linearity: The closeness of a calibration curve to a specified straight line.* Kistler uses "Best Straight Line through Zero" which is defined as follows: Two parallels are sought, as close together as possible but enclosing the entire calibration curve. In addition, the median parallel must pass through zero (no measurand, no output signal). The slope of this median parallel is the Sensitivity of the transducer. Half the interval between the two parallels, expressed as a percentage of full-scale Output (FSO), is the linearity.

Low Impedance: Another name for a piezoelectric transducer with a miniature, built-in charge to voltage converter. Output is typically in mV/mechanical unit. K-SHEAR®, PIEZOTRON®, PICOTRON® and PiezoBEAM® are all forms of low impedance transducers.

Low Pass Filter: An electronic network for passing low and attenuating high frequencies. Many plug-in types are available for Kistler charge amplifiers and couplers.

Measurand: A physical quantity, property or condition which is measured (i.e. pressure, force or acceleration).

Multi-Component Force Transducer: Patented Kistler design utilizing compressive and shear quartz elements for measuring up to three force components and three moments.

Natural Frequency: The frequency of free (not forced) oscillations of the sensing element of a fully assembled transducer.*

Newton (N): A metric unit of force measurement equivalent to 0.2248 ... lb.

picoCoulomb (PC): A unit of electrical charge equivalent to 1 x 10^-12 amps per second.

PICOTRON®: Miniature accelerometer with PIEZOTRON circuitry.

PiezoBEAM®: Low impedance accelerometer. Incorporates a bimorph ceramic element and hybrid charge amplifier for ultra high sensitivity in a small, rugged package.

Piezoelectric Transducer: Transducer with a sensing element that generates an electrical charge when mechanically loaded.

Piezoresistive Transducer: Transducer with a semiconductor bridge as the sensing element. The measuring bridge must be electrically excited to produce an output signal.

Piezoresistive Transmitters: Refers to Kistler piezoresistive pressure transducers with current (4 to 20mA) output. Some have voltage output as well.

PIEZOTRON®: Patented Kistler piezoelectric transducers with miniature, built-in impedance converters (see Impedance Converter).

Polystable: Patented Kistler quartz element incorporated into pressure transducer designs for operating temperatures up to 350°C.

Quasistatic: Term which denotes Kistler's ability to make short-term static or near DC measurements with high impedance transducers and charge amplifiers.

Resonant Frequency: The measurand frequency at which a transducer responds with maximum output amplitude.*

Rise Time: The length of time for the output of a transducer to rise from 10% to 90% of its final value as a result of a step-change of measurand.*

Sensitivity: The ratio of the change in transducer output to a change in the value of the measurand.* Expressed in pC or mV per mechanical unit.

TAP®: Translational-Angular PiezoBEAM. Incorporates a single sensing element that simultaneously measures translational and angular accelerations.

Temperature Coefficient of Sensitivity: The change in sensitivity of a transducer at different (constant) operating temperatures. Typically expressed as a percent change per unit temperature change (%/°C).

ThermoCOMP®: Kistler's new generation of combustion engine sensors. Design incorporates twin diaphragm and TiN coating to minimize thermal shock sensitivity and to protect against abrasions during heavy fuel/oil usage. Other features include high sensitivity; high natural frequency and excellent zero point stability.

Time Constant: (TC) Refers to the discharge time of an AC coupled circuit. In the time domain, a DC signal will decay to 37% of its original value in a period of time equivalent to one time constant.

In high impedance systems, the time constant is the product of the charge amplifier's range capacitor and time constant resistor. In low impedance systems, the system time constant can be approximated by taking the product of transducer and coupler time constants and dividing by their sum.

In the frequency domain, time constant can be related to a high pass filter network with a low frequency cutoff (-5% pt.) equal to 0.5/TC.

Threshold: The smallest change in the measurand that will result in a measurable change in transducer output.*

For charge output transducers, threshold denotes the equivalent noise level in a standard charge amplifier. For voltage output transducers, threshold denotes the equivalent noise level of its built-in charge to voltage converter.

Transverse Sensitivity: The output of an accelerometer caused by acceleration perpendicular to the measuring axis.

TriMOUNT®: PiezoBEAM accelerometer with patented design for mounting via stud, adhesive or internal magnet.

Voltage Output: Output (in mV) from a piezoelectric transducer with a built-in charge to voltage converter (see Low Impedance).

* ANSI/ISA-37.1-1975 (R1982) "American National Standard, Electrical Transducer Nomenclature and Terminology"