TERMINOLOGY

Accuracy | The ratio of error to full scale output (FSO), expressed as a ±X percentage of full scale output. |

A/D converter | A device that converts a continuous analog signal to digitally quantized information. |

Analog output | Output voltage of a system that is a continuous function of the target position relative to the sensor. |

Conductivity | Reciprocal of resistivity. |

Dimensional standard | A standard of measurement or precision reference against which the output of a system is correlated, i.e. a micrometer fixture, feeler gage, precision ceramic spacer, laser interferometer, etc. |

Drift | Undesirable change in system output over a period of time while the sensor/target position is constant. This may be unidirectional or cyclical and caused by such things as aging of the electrical components or environmental changes impacting the system. |

Effective resolution | An application-dependent value determined by multiplying the equivalent RMS input noise specification by the square root of the measurement bandwidth. |

Electrical run out | An error voltage introduced to the output as a result of variations in the permeability of rotating ferromagnetic targets. |

Equivalent RMS input noise |
A figure of merit used to quantify the noise contributed by a system component. It incorporates into a single value factors influencing a noise specification, such as signal-to-noise ratio, noise floor, and system bandwidth. Given a measurement system’s sensitivity and the level of white noise, equivalent RMS input noise can be expressed in actual measurement units. |

Error | The algebraic difference between the indicated displacement and the true displacement of the target. Usually expressed as a percentage of the full scale output. |

Frequency response | The change with frequency of the output/target amplitude ratio (and the phase difference between output and the target) for dynamic targets as applied to a transducer within a stated measuring range. |

Full scale output (FSO) | The voltage output measured at full scale displacement or the maximum displacement for which a system is calibrated. The algebraic difference between the end points. |

Gain | The function of increasing or decreasing sensitivity (see Scale factor/sensitivity). Changing gain will increase or decrease the slope of the output curve. |

Hysteresis | The difference in system output at any given displacement when that displacement is approached first from one direction and then from the opposite direction. When activating switch points, this refers to a designed lag effect between switch point pull-in and drop-out. |

Measurement bandwidth | The difference between the upper and lower frequency response limits of a system. |

Measuring range | The full range of target motion over which the various specifications such as resolution, linearity, and sensitivity can be met. Expressed as the upper and lower limits of a sensor’s measuring capability. |

Noise | Any unwanted electrical disturbance or spurious signal that modifies the transmitting, display, or recording of desired data. |

Non-linearity | The maximum deviation of any point of a calibrated system’s output from a best-fit straight line. Expressed in actual units; e.g. microinches. |

Null gap | The point at which the target is equidistant from each sensor of a differential pair. The system output is expressed as A – B = 0 Vdc. The actual gap is measured from the sensor face to the corresponding target face and includes a desired effect. |

Offset | The required gap between the sensor face and the target at minimum specified range. Offset is required to both optimize performance and prevent the target from striking the sensor face. This is usually specified in mils and dependent upon sensor type. |

Output | The electrical quantity produced by the sensor and modified by the system as a function of target position relative to the sensor. |

Permeability | The ability of a material to become magnetized by an external magnetic field. |

Repeatability | The ability of a system to consistently reproduce output readings when applying the same dimensional standard to it repeatedly, under the same conditions, and in the same direction. |

Resistivity | The resistance to electrical current flow through a unit length and cross sectional area. Express in µΩ-cm. |

Resolution (dynamic) | An application-specific value determined by multiplying the equivalent RMS input noise specification by the square root of the measurement bandwidth. |

Resolution (static <1Hz) | The smallest discernable change in target position relative to a reference. |

Scale factor/sensitivity | The ratio of change in system output relative to a change in target position (volts out per unit of displacement). Expressed as volts or millivolts per mil or millimeter. |

Skin depth | In target thickness, the depth at which the current density is only 36% of the density of the surface. |

Stability | The ability of the system to retain its performance throughout its specified operating and storage life. |

Synchronization | A process where two or more systems are slaved to a master system. This prevents beat note interference (crosstalk) between multiple sensors in close proximity and driven by the same oscillator. |

Thermal sensitivity shift | A change in the slope of the calibration curve (sensitivity) that is a function of temperature only. |

Thermal zero shift | A change in output at zero measurand due to the effects of temperature only. Usually expressed in percentage of full scale output per unit change of temperature. |

Transducer | A device that provides a usable output in response to a specified measurand; e.g. a sensor that converts a mechanical position displacement to an electrical signal. |

Zero shift | Movement of the output curve up or down across the x-axis without changing the slope (gain) or linearity of the curve. |

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