Abbott Firestone Curve
Also known as a Material Ratio Curve. It is a graph showing the percentage of material that would be present after slicing through the surface at varying depths below the highest peak.
Abbott Firestone Curve is often used on cylinder liners for example to check and predict wear characteristics.
Amplitude Distribution
Amplitude Distribution is a graph showing the amount of data points of the profile that would be present after slicing through the surface at various depths below the peak. Amplitude Distribution can aid in analysis by showing whether the surface has more peaks or valleys or more valleys that peaks, or an equal amount of both.
Analogue instrument
This is an instrument that operates with a signal that can vary continuously. Some instruments use analogue electronic signals to represent the profile. On most modern instruments, the signal used for analysis is digital.
Anisotropic Surface
A surface with a directional lay – a visible direction in its roughness.
Arcuate Correction
This is the correction applied to the measured data to compensate for the fact that the stylus (whose arm is pivoted) moves in an arc rather than in a true vertical motion. Not all surface finish instruments have the benefit of arcuate correction. Only when measuring certain types of profile over certain ranges is arcuate correction necessary. Systems that measure form as well as surface finish usually require arcuate correction.
Assessment Length
The data left after filtering used to analyse the surface.
Auto Lift-off
Some instruments have the ability to lift the stylus from the surface after measurement. This can be done by use of mechanisms either on the gauge or by use of a column movement on the instrument. This prevents stylus damage when either moving the stylus back to the start position in the non-measuring direction or for lifting the stylus clear in order to load a new component.
Auto Reverse
A facility to reposition the stylus at the start position automatically after a measurement.
Axis Calibration
For automatic programming and for some types of analysis it is critical that all movement axes (column, arm, and spindle) are capable of being calibrated. If a component is to be measured at known heights then the column on the instrument should have some capability of recording those heights. If horizontal or radial measurements are to be made, then calibration of the instrument’s arm is necessary. Spindle position is critical, especially on roundness instruments and some means of calibrating this is also required.
Balance and phase
This term used to describe the resistive balance and phase characteristics that relate to inductive gauges
Bandwidth
The ratio between Lc Cut-off (upper) and Ls Cut-off (lower) values. For example, on surface finish instruments, if the upper cut-off Lc was 0.8mm and the lower cut-off Ls was 0.008mm, then the bandwidth would be Lc/Ls = 100:1
For roundness instruments the bandwidth would be the ratio between the upper and lower filters. For example, a 50 – 500 UPR filter would have a bandwidth of 500/50 = 10:1.
Bearing Ratio
Alternative term for Material Ratio
Calibration
A set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument and the corresponding known values of a standard.
Calibration Constant
A numerical value which is used to compensate for inaccuracies in an instrument
Calibration Standard
A test artefact, or master reference item, having known values
Center Line
A reference line parallel to the general direction of a profile, which divides the profile into two equal parts.
Co-axiality Value
The diameter of a cylinder that is coaxial with the datum axis and will just enclose the axis of a second cylinder.
Co-ordinate System
All measured points on a metrology instrument will have some form of
co-ordinate. For example, a surface measured using a roughness instrument will collect data whose co-ordinates will consist of x (arm movement) and z (gauge movement) values.
On a roundness system a roundness plane’s data may have co-ordinates for radial (arm position and gauge reading), height (column position) and angular (spindle position) values.
Concentricity
Concentricity is twice eccentricity and can be described as the diameter of a circle that is created when the centre of a component is rotated around the datum axis. Two roundness planes can be considered concentric if they have the same centre.
Contact Direction
This relates to the measuring direction of the stylus. If an operator was measuring a component for flatness on a surface facing upwards, then the contact direction would be down.
Contact Speed
The speed at which an axis moves when commanded to move into contact with the component.
Crowning (cresting)
For surface measurement, crowning (sometimes referred to as cresting) is the process of determining the highest point of a component that has a convex form, or the lowest point of a concave form. On some instruments crowning can be done automatically by using the measured data.
The term Cresting is more properly applied to the alignment of the stylus to the axis of rotation of an instrument designed for the measurement of roundness. See section on cosine errors.
Cut-off
In basic terms, a cut-off is a filter and is used as a means of separating or filtering the wavelengths of a component. Cut-offs have a numerical value that when selected will reduce or remove the unwanted wavelengths on the surface. For example, a roughness filter cut-off with a numeric value of 0.8mm will allow wavelengths below 0.8mm to be assessed with wavelengths above and around 0.8mm being reduced in amplitude; the greater the wavelength, the more severe the reduction. For a waviness filter cut-off with a numeric value of 0.8mm, wavelengths above 0.8mm will be assessed with wavelengths below 0.8mm being reduced in amplitude.
Cut-off Length
A term often used to mean the same as Sampling Length.
Cylindricity
The amount by which a part departs from a perfect cylinder.
Data Collection
The term used to describe the action of drawing the stylus across the component and acquiring data from a transducer.
Datum
A fixed reference to which analysed data can be compared. For example, when measuring cylindricity, it is possible to store the cylindricity axis as a datum. It is then possible to use this is a reference for further analysis such as measuring flatness of the cylinder top and analysing for squareness to the stored cylinder axis.
Eccentricity
The amount by which the centres of two shapes are displaced from one another in a single plane, or, if in separate planes, relative to an axis which is at 90? to the reference plane
EIM
Electronic Interface Module. The device which provides the interface between the instrument and the controlling computer.
Evaluation Length
The length of the data used for analysis. This will be different in most cases from the measurement length.
Filtered Profile
The profile representation after passing through a filter. This can also be termed as 'modified data' and is different from raw or measured data because it has been adjusted or modified in some way by filtering or form removal etc.
Flatness
Flatness can be analysed by quantifying deviations from a least squares reference plane. A least squares reference plane is a plane where the areas above and below the plane are equal and are kept to a minimum separation. Flatness is calculated as the highest peak to valley normal to this reference plane.
Flatness can also be analysed by a minimum zone calculation, defined as two parallel planes that totally enclose the data and are kept to minimum separation. The flatness error can be defined as the separation of the two planes.
Form
The overall ‘shape’ of the object under test.
Form Analysis
The calculation carried out in the software which creates a form fit. For example, if a bearing is to be measured that is designed to be a true arc, it is possible to fit a best fit arc to the data in order to assess the deviations from it. It is the variation between this form fit and the real profile which enables form parameters to be calculated.
There are many types of form analysis based on measuring and comparing the actual form to the desired form
Form Fit Exclude
Marking of those parts of a profile displayed in Data Selection View which are not to be used in calculation of the form fit. For example as ‘hole’ in the surface profile.
Gauge
The gauge on most measuring instruments is a transducer that converts mechanical or optical measurement into a signal in order to carry out an analysis of the component. Sometimes called the 'pick up' or 'probe'.
Gauge Calibration
This is the measurement of an appropriate calibration standard (ball, flick, prism or 3-line standard) to derive a set of calibration constants. These constants will be used in any calculations to ensure integrity of results.
Gauge Range
This is the linear distance over which the gauge can measure. It should be noted that the specific gauge doesn't always dictate the range, changing the stylus from one length to another will affect and change the range.
Gauge Resolution
The smallest numerical value that the gauge can resolve a defect.
Harmonic
A harmonic is a repeated undulation in 360?. For example a third harmonic has 3 undulations of equal wavelength in 360?. Any surface can be broken down into its individual harmonic elements. The ability to analyse harmonics is very useful in order to predict a component’s function or to control the process by which the component is manufactured.
Inductive Gauge
A type of transducer for converting the movements of the stylus into electrical signals. An inductive transducer employs the very small movements of the stylus to move an armature between two coils to change their relative electrical inductance. The amplitude and direction of these changes provide the output from the gauge.
Interferometric Gauge
The application of interferometery to a gauging system (application of light wave interference phenomena for measurement purposes).
Isotropic Surface
A surface having no directional lay – no obvious pattern direction, grinding for example.
Kurtosis
Kurtosis is a measure of the sharpness of the surface profile.
Lay
Many machined surfaces will have a distinct directional characteristic which is called a lay. Lay refers to the predominant direction of the surface texture. Ordinarily lay is determined by the particular production method and geometry used.
Surfaces having a directional lay are called anisotropic while those without a predominant lay direction are isotropic. It is sometimes necessary, if the lay is functionally important, to specify on drawings the direction or type of lay. For example, a turned cylinder will have a lay that is at right angles to its axis.
Lc Cut-off
The Lc Cut-off specifies the high pass cut-off length for the selected filter. Wavelengths around and greater than this length will be removed or attenuated in amplitude by the filtering process.
Least Squares Circle
The Least Squares Reference Circle is a circle where the sum of areas inside this circle are equal to the sum of the areas outside the circle and kept to a minimum separation.
Least Squares Cylinder
The least squares cylinder is constructed from the average radial departure of all the measured data from the least squares axis.
Least Squares Line
A least squares line is a line through a profile such that the sum of the squares of the deviations of the profile from the mean line are at a minimum.
The most common application of a least squares mean line is to "level" the measured profile by calculation rather than mechanical means.
Local Peak
A local peak is a region of a profile between two successive local valleys in the profile.
Local Valley
That part of a profile flanked by a peak on either side.
Ls Cut-off
The Ls Cut-off specifies the low pass cut-off length for the selected filter. Wavelengths around and less than this length will be removed or attenuated in amplitude by the filtering process.In a primary analysis, Ls is the only cut-off specified.
Material Ratio
The ratio of the length of surface at any specified depth in the profile to the evaluation length, expressed as a percentage.
Maximum Inscribed Circle
The Maximum Inscribed Circle is a reference circle of maximum radius that is totally enclosed by the measured profile. (Roundness measurement only)
Mean line
The mean line for the primary profile is determined by fitting a least squares line of nominal form through the primary profile. The mean lines for the roughness and waviness profiles are defined by profile filters as detailed in ISO 11 562.
Measured profile
The representation (usually trace) of the profile obtained by a roundness or surface texture measuring instrument. This is usually raw data and not analysed data.
Measurement Axes
The axes from which the direction of measurement is taken.
Micron
1 Micron is 1,000,000th of a meter or 1,000th of a mm.
Minimum Circumscribed Circle
The smallest reference circle which totally encloses the measured profile. (Roundness measurement only)
Minimum zone circle
The minimum zone circle can be described as the total separation of 2 concentric circles which totally enclose the data and are kept to a minimum separation.
(Roundness measurement only)
Modified Profile
This is the profile that remains after filtering or manipulating the measured profile. For example, Primary, Roughness and Waviness profiles (associated with surface finish) are all modified profiles as the measured data has been filtered
Nanometre (nm)
1 nanometre is 1,000,000,000th of a metre or 1,000,000th of a mm.
Origin
The point that is regarded, by definition, as being 0,0 in terms of co-ordinates.
Parallelism
There are different ways of measuring parallelism. For specific information please consult the type of measurement. For example, cylindricity, flatness, straightness.
Parameter
Terms used to analyse characteristics of a measured component in quantitative terms. For example, Ra is a parameter that quantifies Roughness Average of a surface profile.
PGI
Phase Grating Interferometric transducer. This device is housed within a gauge and converts the movements of the stylus into an electrical signal. This type of transducer employs a laser diode in conjunction with a fine optical grating to detect very small movements of the stylus and provides a high resolution output of both amplitude and direction.
Pick up
Also referred to as the gauge. This can take the form of an electrical transducer which converts movement of styli into electrical signals
Pitch
The "straight line", or Euclidean distance, between the origin and the feature or measurement point. For example, the centres of two circle.
Plug Gauge Circle
See Maximum Inscribed Circle definition.
Primary Filter
This is a low pass filter used on the measured data in order to remove or reduce wavelengths around or below the value of this filter.
Primary Parameters
Parameters used to quantify the primary profile
Primary Profile
The primary profile is the traced profile after subtracting the form
(see Form Analysis) and subjecting it to a low pass filter.
Profile
A section taken through a workpiece. When using surface finish equipment, the profile is the trace made of the real profile. The Roughness, Waviness and Primary analyses show the modified profile.
Qualifier
The optional variable(s) used in the calculation of a parameter. For example, High Spot Count (HSC) requires a reference line in order to calculate the number of peaks passing through that line. This reference line needs qualification of its positional height. This prompts input from the user and the term qualifier is used for this type of parameter.
R & W
An assessment of roughness and waviness components of a profile based upon surface characterisation by the Motif Method. See ISO 12085. This method of roughness and waviness calculation was developed by the French automotive industry.
Raw Profile
A display of the surface without any filtering or form removal applied. Usually the measured data prior to analysis.
Ring gauge circle
See “Minimum Circumscribed Circle”
Roughness
This is usually the process marks or witness marks produced by the action of the cutting tool or machining process, but may include other factors such as the structure of the material.
Roughness Filter
Selecting a roughness filter will remove waviness elements, leaving the roughness profile for evaluation.
Run-up Length
The amount of travel allowed for a traverse mechanism to stabilise before data collection begins. Most measuring instruments also have a run down length.
Runout
Runout is a useful parameter in that it combines the effect of form error and concentricity to give a predicted performance when rotated about a datum.
Sample Length
After the data has been filtered using a cut–off, we then sample it. Sampling is done by breaking the data into equal sample lengths. The sample lengths have the same numeric value as the cut-off.
Skid
The small polished 'sledge' or 'follower' on the end of the nosepiece which maintains contact with the component to shorten the measurement loop and provide a reference data
Spacing parameters
The features that determine a spacing parameter usually relate to peaks and valleys or to average wavelengths. Spacing refers to the distance between features on a profile in the x direction, parallel to the nominal direction of the trace.
Stylus
When measuring surface finish or roundness by contact method, some means of touching the surface is required. A stylus can be likened to a gramophone needle and is used as a means of transferring information to a gauge or transducer by means of deflection.
Transducer
A device that converts movement to an electrical signal output in order to represent the surface or measurement under test.
Traverse Length
The full distance over which the stylus is drawn for a data collection operation.
Undulations
The peaks and valleys on the periphery of a profile.
Waviness
This is usually produced by instabilities in the machining process, such as an imbalance in a grinding wheel, or by deliberate actions in the machining process. Waviness has a longer wavelength than roughness which is superimposed on the waviness.
It should be noted that there are no guidelines that indicate when wavelength can be considered to be waviness. On optical components, the considered waviness wavelength may be equal to the roughness wavelength on an automotive component.
Waviness Filter
A filter that separates roughness from waviness to leave the waviness profile for analysis.