- High Cost Service Applications
- Heavy Loads
- Corrosive or Washdown
- Temperature Extremes
- Wet or Dirty Environments
- Electrically Noisy Environments
Air Gap - The distance between the face of the magnet and the face of the sensor.
Total Air Gap - The distance between the face of the magnet and the active sensing element inside the sensor housing.
Closed Circuit This exists when the flux path external to a permanent magnet is confined within high permeability materials that compose the magnet circuit.
Coercive Force (Hc) The demagnetizing force, measured in Oersteds, necessary to reduce observed induction, B, to Zero after the magnet has previously been brought to saturation.
Curie Temperature (Tc) The temperature at which the parallel alignement of elementary magnetic moments completely disappears, and the material is no longer able to hold magnetization.
Demagnetization Curve The second quadrant of the hysteresis loop, generally describing the behavior of magnetic characteristics in actual use, also known as the B-H curve.
Eddy Currents Circulating electrical currents that are induced in electrically conductive elements when exposed to changing magnetic fields, creating an opposing force to the magnetic flux. Eddy currents can be harnessed to perform useful work (such as damping of movement), or may be unwanted consequences of certain designs which should be accounted for or minimized.
Ferromagnetic Material A material whose permeability is very much larger than 1 (from 60 to several thousand times), and which exhibits hysteresis phenomena.
Fringing Fields Leakage flux particularly associated with edge effects in a magnetic circuit.
Induction (B) The magnetic flux per unit area of a section normal to the direction of flux. Measured in Gauss, in the cgs system of units.
Intrinsic Coercive force (Hci) Measured in Oersteds in the cgs system, this is a measure of the material's inherent ability to resist demagnetization. It is the demagnetization force corresponding to zero intrinsic induction in the magnetic material after saturation. Practical consequences of high Hci values are seen in greater temperature stability for a given class of material, and greater stability in dynamic operating conditions.
Irreversible Loss Defined as the partial demagnetization of a magnet caused by external fields or other factors. These losses are only recoverable by remagnetization. Magnets can be stabilized to prevent the variation performance caused by irreversible losses.
Isotropic Magnet A magnet material whose magnetic properties are the same in any direction.
Magnetic Field Strength (H) A measurement of the magnetic ability to induce a magnetic field at a given point. This is measured in Oersteds.
Magnetizing Force (H) The magnetomotive force per unit length at any point in the magnetic circuit. this is measured in Oersteds.
Magnetomotive Force (F) The magnetic potential difference between any two points.
Maxwell A unit of magnetic flux. One Maxwell is one line of magnetic flux.
Oersted, Oe A unit of magnetic field strength or magnetizing force.
Orientation Direction The direction in which an anisotropic magnet should be magnetized in order to optimize the magnetic properties.
Saturation This is a condition where all magnetic moments have become oriented in one direction.
Accuracy is a measure of how close the output is to where it should be. It is usually expressed in units of distance, such as ±30 arcseconds or ±0.0001 inch. If it's expressed as a percent, make sure to state whether it's a percent of full scale (not usually meaningful with a rotary encoder) or a percent of nominal resolution.
Angular Misalignment is the maximum deviation in perpendicularity between the encoder shaft and the face of the mounting surface. It is the total of shaft misalignment, shaft runout and mounting face runout.
Bit is an abbreviation for BInary digiT; it refers to the smallest element of RESOLUTION.
CPR can mean either cycles/rev or counts/rev. To avoid confusion, this term should not be used.
Error is the algebraic difference between the indicated value and the true value of the input.
Frequency Response is the encoder's electronic speed limit, expressed in kilohertz (1 kHz = 1000 Hz = 1000 cycles/sec). For calculations, rotational speed must be in rev/sec (rps = rpm/60); linear speed must be either in/sec or mm/sec, depending on the scale line count.
(cycles/rev) x (rev/sec)/1000 = kHz
Index Signal is a once-per-rev output used to establish a reference or return to a known starting position; also called reference, marker, home, or Z
Interpolation involves an electronic technique for increasing the resolution from the number of optical cycles on the disc or scale to a higher number of quadrature square waves per revolution or per unit length. These square waves can then be QUADRATURE DECODED.
Measuring Step is the smallest RESOLUTION element; it assumes QUADRATURE DECODE.
PPR = Pulses per revolution.
Commonly (but mistakenly) used instead of cycles/rev when referring to QUADRATURE square wave output.
Quadrature refers to the 90-electrical-degree phase relationship between the A and B channels of incremental encoder output.
Quadrature Decode (or 4X Decode) refers to the common practice of counting all 4 quadrature states (or square wave transitions) per cycle of quadrature square waves. Thus, an encoder with 1000 cycles/rev, for example, has a resolution of 4000 counts/rev.
Quantization Error is inherent in all digital systems; it reflects the fact that you have no knowledge of how close you are to a transition. It is commonly accepted as being equal to ±1/2 bit.
Quantum (plural is QUANTA) = BIT. It is the smallest RESOLUTION element. (QUANTA and BIT are more commonly used with absolute encoders; counts/rev or MEASURING STEPS are more common with incremental encoders.)
Repeatability is a measure of how close the output is this time to where it was last time, for input motion in the same direction. It's not usually specified explicitly, but it is included in the accuracy figure. (As a rule of thumb, the repeatability is generally around 1/10 the accuracy.)
Resolution is the smallest movement detectable by the encoder. It can be expressed in either electrical terms per distance (e.g., 3600 counts/rev or 100 pulses/mm) or in units of distance (e.g., 0.1° or 0.01 mm).
Slew Speed is the maximum allowable speed from mechanical considerations. It is independent of the maximum speed dictated by FREQUENCY RESPONSE.