E014 - Glossary of Loadcell Terms
This glossary contains brief definitions of commonly used loadcell terms. Some of the terms are explained in greater detail on other Engineering Sheets.
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AL |
Applied load. |
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Average output of a loadcell, obtained from tension and compression outputs at rated load. |
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Axes |
Plural of axis. |
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Axial |
Relating to a single axis. |
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Axial compensated |
Exhibiting extraneous force immunity that is focused solely on the preservation of measurement integrity on a single measurement axis. |
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A fixed reference line referring to a single orientation of applied load. |
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A reaction caused by the application of a force at a distance from the loadcell force centre, off line from the principal axis. |
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Operating in both tension and compression |
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The complete wired arrangement of strain gauges, modulus resistors and zero balance elements within a 'Wheatstone Bridge'. |
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Bridge resistance |
The electrical resistance of the loadcell bridge circuit measured at the excitation connections of the loadcell in the presence of no external influences. Expressed in ohms (Ω). |
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The theoretical point through which calibration load will be applied if it is known that the real-world load application will not pass through the force centre. Note that this is required for all multi-axis loadcells. |
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Creep |
The slow and progressive change in loadcell output that occurs with time following the application of a static load with environmental and other variables remaining constant. Expressed as a percentage of the applied load over a specified time (usually 20 mins). |
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The erroneous output that results in one axis as a result of loading in another separate orthogonal axis. Common in multi-axis loadcells due to the unavoidable mechanical coupling between the sensing elements. |
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Relating to a load that is reducing towards zero in either tension or compression. |
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A 'live' load that regularly changes with time, or involves a cycle or driven actuation, as opposed to a static load. |
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EFI |
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The supply voltage to the bridge circuit delivered through two colour coded wires, one positive and one negative. |
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Excitation voltage - Maximum |
The maximum voltage that can be supplied to the bridge circuit without permanent damage to the loadcell. Expressed in Volts (V). |
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Excitation voltage - Recommended |
The optimum voltage that should be supplied to the bridge circuit to ensure the loadcell maintains its performance specification. Expressed in Volts (V). |
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The ability to significantly reduce errors resulting from cross talk or off axis loads, either through mechanical design or electrical compensation of the bridge circuit. |
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An approximate measure of the total number of times a loadcell can be subjected to a complete load cycle up to full rated load, without a change in performance. Expressed as a number of rated load cycles. |
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A physical product of an object's mass and acceleration. The most common example is an object's weight, which is a product of it mass and the acceleration due to gravity. Note that the scientific unit for weight is the Newton and not the kilogram. This gives rise to the concept of kilogram force, widely used in our labelling (abbreviated to kgf). |
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The theoretical point through which the force should be applied to avoid off axis loads. This will always be along the principal axis. If this is not possible, the variance should be made clear when discussing a loadcell application with our engineers. See also calibration centre. |
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A measure of an amplifier's ability to increase the amplitude of a signal, such that the output is greater than the original input. |
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Hysteresis |
The maximum deviation in loadcell output from the same applied load during decremental loading when compared to incremental loading. Expressed as a percentage of rated load. |
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Relating to a load that is increasing towards rated load in either tension or compression. |
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Insulation resistance |
The resistance measured between the bridge circuit and metal of the loadcell body. Expressed in megohms (MΩ) at a stated voltage (V). |
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A measure of how much error may occur if two loadcells are swapped without altering the scaling of the associated instrument. This arises from variations in span from one loadcell to another. Rationalised loadcells of the same type can be swapped for minimal error. See rationalisation tolerance. |
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A unit of force defined as the mass of one kilogram multiplied by the acceleration due to gravity. |
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Load |
The force applied to the loadcell. Expressed in appropriate scientific or engineering units such as the Newton or kilogram force. |
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A single peak to peak duration of varying load either between zero and rated load, or encompassing both tension and compression in the case of a bi-directional loadcell. Continuous load cycles up to full rated load are considered in the estimation of fatigue life. |
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Elements within the bridge circuit used to provide temperature compensation for span drift. See temperature range - compensated. |
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Relating to any loadcell that is designed to measure load inputs on more than one axis. |
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A unit of force defined as that required to give a mass of one kilogram an acceleration of one metre per second per second. 1kgf = 9.80665N. |
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The maximum deviation in loadcell output from a straight line, which can be drawn between zero load output and rated load output, during incremental loading. Expressed as a percentage of rated load. |
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Normalisation |
See rationalisation. |
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Any load that does not pass through the force centre of the loadcell. Also often used to describe general extraneous forces, which typically include bending moments and sideloads. |
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Output symmetry |
The difference in the rated output for tension and compression, for a universal loadcell, with respect to the average output (AO). Expressed as percentage of average rated output. |
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Overload - Safe |
The maximum load in excess of the rated load that can be applied along the principal axis without a permanent degradation in loadcell performance. Expressed as a percentage of the rated load. |
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Overload - Ultimate |
The maximum load in excess of the rated load that can be applied along the principal axis without a serious risk of structural damage or failure. Expressed as a percentage of the rated load. |
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The electrical summing and averaging of multiple loadcells outputs to achieve a singular output signal. This is typically implemented so that a single piece of instrumentation can be used measure the total load experienced by a given number of loadcells. This should only be done with rationalised outputs and care must be taken to ensure that the instrument is capable of powering the required number of loadcells. This information is given on the individual instrumentation data-sheets. |
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The axis along which the loadcell is intended to be loaded. |
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The maximum load that a loadcell is designed to measure. Expressed in appropriate engineering units such as the Newton or kilogram force. Individual loadcell data-sheets often provide multiple ranges to choose from, each measuring from zero load to full rated load. |
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The nominal output obtained when the loadcell is loaded to the rated load. Expressed in millivolts per volt (mV/V). |
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Rated output - Rationalised |
The output obtained when the loadcell is loaded to the rated load, subject to rationalisation. Expressed in millivolts per volt (mV/V). |
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Relating to a loadcell that has undergone rationalisation. |
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The process of trimming a loadcell output at the rated load specific target value, with a tight rationalisation tolerance. Required for parallel connection, interchangeability or to suit the limited gain adjustment of some amplifiers. |
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An extremely small variance from a predetermined output after rationalisation, such that two rationalised loadcells of the same type are almost identical, facilitating increased interchangeability of parts. The rationalisation tolerance is provided on each loadcell data-sheet. Expressed as a percentage of the rated load. |
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Repeatability |
The maximum deviation in loadcell output during successive measurements of the same given load, applied in the same direction. |
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The smallest step change in applied load that can be accurately measured by the loadcell. See scaling. |
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RL |
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RO |
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A calibration function stored within an instrument. Expressed as rated load x resolution (for example 500 x 0.1kgf indicates 5000 steps of 0.1kgf resolution within a 500kgf rated load). |
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Screen |
A colour coded wire for connection at the instrument only, provided to help reduce electrical noise. |
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Sense |
See voltage sensing. |
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An extraneous force perpendicular to the desired measurement axis |
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The voltage output from the bridge circuit delivered through two colour coded wires, one positive and one negative. |
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The full mV/V range between zero load output and rated output. |
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A long term consistent load that does not vary much with time, as opposed to a dynamic load. |
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Where a specified variable is no longer changing with time. |
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Resistive element for which the electrical resistance is a function of the applied strain. |
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Temperature effect on rated output |
The change of rated output for a specified temperature change at steady state conditions. Expressed as a percentage of the output per °C. |
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Temperature effect on zero load output |
The change of zero load output for a specified temperature change at steady state temperature conditions. Expressed as a percentage of the rated output per °C. |
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The temperature range over which the loadcell will maintain its stated performance specification. |
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Temperature range - Safe |
The temperature range over which the loadcell may be used and experience no permanent degradation in loadcell performance. |
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Traceability |
The ability to verify the accuracy of loadcell calibration through common standards, practices and documentation. Calibration certificates are supplied as standard for all loadcells and systems that have been calibrated to traceable standards. A calibration uncertainty document is available for download under the information button. |
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See bi-directional. |
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A method using two colour coded wires, one positive and one negative, to 'sense' and correct for voltage drop. A loadcell with 6 wire 'voltage sensing' cable will not have its calibration invalidated should the length of cable be later changed from its original specification. |
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A circuit of resistive elements connected to form a quadrilateral. Used in strain gauge loadcells as a form of potential divider, such that changes in resistance can be amplified and measured to calculate the magnitude of an unknown force applied through the loadcell. |
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Relating to the zero load output and/or the components used to trim the zero load output to within data-sheet specification. |
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The loadcell output when it is not subject to a load of any kind. Expressed as a percentage of rated output. |
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A calibration comprising 3 incremental load points followed by 2 decremental load points, to give measurements at 0%, 50%, 100%, 50% and 0% rated load sequentially. This is the minimum number of points that are needed to assess all aspects of a loadcell's performance. For a bi-directional calibration the same is repeated for each direction. |
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5 Point calibration |
A calibration comprising 5 incremental load points followed by 4 decremental load points, to give measurements at 0%, 25%, 50%, 75%, 100%, 75%, 50%, 25% and 0% rated load sequentially. This gives a better picture of the non-linearity than a 3 point calibration. Some instruments come with a linearisation feature which can help to mitigate some of this error if provided with enough calibration points.For a bi-directional calibration the same is repeated for each direction. |
