Terms and definitions
| Accuracy | A qualitative concept that defines the extent to which the weight readouts of a scale approach the true value of the quantities weighed. Accuracy is quantified by an instruments readability, standard deviation, resolution, accuracy class or the uncertainty of measurement given (e.g. in a DKD or NKO calibration certificate). See also “Error calculations”. | |||
| Accuracy class | Class divisions according to the specific metrological requirements of OIML or verification standards for weighing instruments or for weights. | |||
| Actual scale interval | See “scale interval”. | |||
| Adjustment | Adjusting (= intervention in) a weighing instrument so that the deviation between the displayed value and the true mass is reduced as much as possible, and, at the very least, the instruments maximum permissible errors are not exceeded. It is especially necessary to re-adjust the sensitivity of high-resolution balances each time they have been moved to a different location. Many of these instruments have a built-in weight to do this. | |||
| Automatic weighing instrument | A weighing instrument that does not require the intervention of an operator during weighing. Example: a checkweigher integrated into a conveyor belt. | |||
| Autotaring / autozero | See “Zero tracking device”. | |||
| Auxiliary indicating device | Analog indicator: Device for interpolation between two scale marks. Digital display: An additional, specially identifiable, numeric display with a scale interval less than the verification scale interval “e” (on weighing instruments acceptable for legal verification) | |||
| Calibration | Calibration determines the relationship between the displayed value and true mass by comparison with a known mass. During calibration no intervention occurs which would change the parameters of the weighing instrument (Then it would be Adjustment). The result of calibration is a measured value and and a value for uncertainty of measurement. | |||
| Complimentary indicating device | See “Auxiliary indicating device” | |||
| Conventional mass | The conventional mass of an object is equal to the mass of a standard with a density of 8.000kg/m³, which keeps this object in equilibrium at 20°C and an air density of 1.2kg/m³. | |||
| Corner load error | See “Eccentric loading error”. | |||
| Deviation | See “Error of measurement”. | |||
| Digit (d) | Abbreviated term for scale interval (refer to “Scale interval”). | |||
| Discrimination threshold | The value of the smallest change in load that is gently added or removed from the weighing pan and that results in a perceptible change in the readout displayed. | |||
| Disturbance | A quantity that is not the subject of a measurement, but influences the weighing result, and is outside the specified rated operating conditions of the instrument. | |||
| Drift | Gradual change in the readout of a weighing instrument at a constant load (see “instrument errors“). | |||
| Dual range Instrument | See “Multiple range instrument”. | |||
| Eccentric loading error | Also referred to as “corner load error” or “off-center loading error”. This is the change in readout when the same object is placed in various positions on the weighing pan. | |||
| Error (of measurement) | Difference between the displayed value and the true or reference value (often called deviation). | |||
| Gravitational acceleration (g) | The acceleration imparted to an object by attraction due to gravity. Gravitational accelleration depends on the location: Due to centrifugal force, it is less at the equator than at the poles of the earth. It also decreases as the altitude increases. The mean value for g on earth is 9.8 m/sec². Gravitational acceleration is simultaneously the proportionality factor between the weight “W” and the mass “m” of a body: W = m . g. Other terms for g : “acceleration of gravity”, “acceleration of free fall”, “apparent gravity”, “earths attraction”. | |||
| Hysteresis | Hysteresis means that at a constant load , the displayed value depends on the previous load. Quantitavily, hysteresis is expressed as the difference between the readouts obtained when the same load is weighed once following a lighter load and once following a heavier load. Hysteresis occurs particularly with strain-gauge load cells and weighing instruments subject to mechanical friction. | |||
| Integration time | The time during which the instantaneous weighing signal is totaled and averaged in a weighing instrument. A long integration time yields good results in suppressing interference, a short integration time allows rapid response to changes. | |||
| IP protection | Degrees of protection, indicated by the abbreviation IP (International Protection) and two reference numbers, specifying the degree of protection of electrical equipment against contact an ingress of solid foreign bodies or dust (the first number) and water (the second number). For details on this see European standard EN 60529. | |||
| Kilogram | Unit of measure for mass. | |||
| Kilogram prototype | See “prototype” | |||
| Level indicator or spirit level | Device used as a guide to find the horizontal position of a balance or scale. Usually consists of a small, liquid-filled, slightly curved container in which an air bubble shows the highest point. | |||
| Linearity error, Linearity | The deviation from the theoretically straigt-lined Linear slope of two interdependent values. For weighing instruments this means the positive or negative deviation of the readout from the actual load, when the zero point and the span have been correctly adjusted. See also the chapter “Errors” on this page. | |||
| Mass comparator | Common term for extremely accurate balances used for comparing weights. Often these instruments have a limited weighing range that does not start at zero, and very high readability. For instance: from 9.9900000kg to 10.0500000kg for a comparator that is used for 10kg weights. | |||
| Mass unit | Physical quantity, A base unit of the international system of units (SI). | |||
| Material measure | A device intended to reproduce or supply, in a permanent manner during its use, one or more known values of a given quantity. | |||
| Maximum capacity (max) | Upper limit of the weighing range. It does not take into account the additive tare capacity of a tare device (see “Taring”). | |||
| Maximum permissible errors in use / in service | Limits of error of a legally verified weighing instrument, which must not be exceeded when this instrument is operated. The max. perm. errors in use are twice the maximum permissible errors on initial and subsequent verification. | |||
| Maximum permissible errors on verification | Limits established in a table for the errors of measurement of a weighing instrument. These must not be exceeded during verification. | |||
| Measurement standard | See “standard”. | |||
| Minimum capacity | Lower limit of a weighing range on a legally verified instrument. The value of a load below which the weighing results may be subject to an excessive relative error. Therefore, a weighing instrument may not be used below its minimum capacity. | |||
| Multi-interval | See “variable scale interval”. | |||
| Multiple range instrument | Weighing instrument that has two or more weighing ranges, which differ in their maximum capacity and scale interval. Each range extends from zero to its individual maximum capacity. | |||
| Newton | (N) Unit of force. 1 N = 1 kg . 1m/sec2; | |||
| Non- automatic weighing instrument | A non-automatic weighing instrument requires the intervention of an operator, e.g. to place the load on the scale and to obtain the weighing result. | |||
| OIML | Organisation Internationale de Métrologie Légale. International organisation for legal metrology, located in Paris, which is responsible for standardization of legal metrology in the associated countries. | |||
| Overload protection | A locking device which prevents weighing above the maximum capacity of a scale or which protects components from overloading and damage. | |||
| Polyrange | See “variable scale interval”. | |||
| ppm | Abbreviation for parts per million; 1ppm =  . | |||
| Prototype | The prototype is the material measure of a primary standard. | |||
| Range of uncertainty | In automatic checkweighers , which sort objects according to several weight classes: The range within which the checkweigher is unable to allocate an object to a specific class. | |||
| Readability | Smallest difference that can still be read on a display. For balances and scales with a scale indicating device (analogic), the readability is equal to the smallest fraction of a scale interval that can still be estimated with reasonable reliability or which can be determined by an auxiliary device. For balances and scales with a numeric indicator (digital display), the readability is equal to one digital step. | |||
| Repeatability | The ability of a weighing instrument to display corresponding results under constant testing conditions, when the same load is repeatedly placed onto the weighing pan in the same manner. In general, the difference between the largest and the smallest result is used to specify this quantity. | |||
| Reproduceability | See previous term: Repeatability. | |||
| Resolution | A term that has not yet been precisely standardized. It is commonly used for the quotient of the maximum capacity and the readability (“a resolution of 10000 steps or digits”), or for the readability (“a resolution of 0.1g”). | |||
| Response time | Corresponds to the stabilization time | |||
| Scale interval (d) | For weighing instruments with an analog indicator: The difference between the values, corresponding to two consecutive scale marks. For instruments with a digital display, this is the smallest digital step; i.e., the difference between any two consecutive indicated values. | |||
| Sensitivity | Change in the displayed value divided by the load on the weighing instrument, which causes this change. For a correctly adjusted weighing instrument with a digital display, the sensitivity must always be exactly 1.0g/g=1.0 . For a scale with an analog indicator, the sensitivity can also be indicated in scale divisions/g or mm/g. | |||
| Span | Difference between the indication of a weight at the instruments maximum capacity and the indication at zero load. | |||
| Stabilization time | The time between complete placement of an object on the pan and display of the final result. | |||
| Stability | For mechanical balances / scales: The mechanical system has stopped moving. For Electronic balances / scales: Two or three consecutive readouts do not deviate by more than the limits of the previously selected stability range. | |||
| Stability control / Stability detector | In electronic balances / scales: An electronic circuit or program for monitoring whether a readout is still changing. The severity of this control can be pre-adjusted by selecting the stability range. Some balances additionally allow a delay time to be set. | |||
| Standard | Material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit. In weighing technology, these are primarily weights that are used as mass standards. The standards with the highest accuracy are called primary standards or prototypes. | |||
| Standard deviation | A mathematic quantity for evaluating a weighing instrument (or a sequence of measurements) in terms of repeatability: The standarddeviation “s” is defined as:
To determine the standard deviation with sufficient certainty, the number of measurements must be high enough (at least 6). | |||
| Standby | Operating state of electronic equipment in which one part of the components is switched off, while another part is still on. The standby mode is used to save energy (e.g. when using batteries), to protect aging-sensitive components, or to attain the instruments operating temperature as soon as possible after switching on. | |||
| Taring | Zeroing the display when a weighing instrument is loaded. This allows the weight readout of an empty container to be reset to zero and the net weight to be read after filling the container. A subtractive taring device reduces the available weighing capacity by the tare value; an additive taring device does not. | |||
| Temperature coefficient | The change of a measured value, (e.g. zero point or sensitivity) when the temperature changes, divided by the degree of temperature change. | |||
| Temperature compensation | A device or measure that either reduces or eliminates the influence of a change in temperature on mechanical or electronic systems. | |||
| Traceability | The property of a result of measurement whereby this result must be related to a national or international standard, through an unbroken chain of documented comparisons. | |||
| Uncertainty (of measurement) | The uncertainty of measurement “u” specifies the range for a measured value, within which the unknown, error-free result lies, usually with a statistical certainty of 95%. (This corresponds to u=2s, see also the chapter “errors”). | |||
| Variable scale interval | Weighing instruments with readouts in partial weighing ranges; for example 60g readable to 0.1 mg; between 60g and 120g, to 0.2mg; and between 120g and 200g, to 0.5mg. The variable scale interval depends on the net weight displayed. Therefore, after taring, the display will start with the smallest scale interval. Also called “multy-interval” or “Polyrange” instruments. | |||
| Verifiable weighing instrument / Weighing instrument acceptable for verification. | Weighing instrument whose type has been tested for conformity and accepted for verification by the approval authorities (“notified body” in the EU). | |||
| Verification | Verification comprises the metrological tests to be performed in accordance with the legal verification requirements and subsequent marking (stamping). The marking certifies that the weighing instrument, at the time of testing, met the legal verification requirements. Verification is carried out by the local verification officer who is responsible for metrological testing and approval. Since 1993, verification of a weighing instrument for use as a legal measuring instrument can also be obtained through manufacturers with an approved quality assurance system. | |||
| Verification scale interval ( e ) | A scale division expressed in legal mass units (mg, g, kg, ct). This division is used for classification of balances and scales and refers to the permissible tolerances. See chapter “Tables”. | |||
| Warm-up time | The time span from switching on the instrument on to the moment at which the instrument is capable of providing the accuracy indicated on its specifications sheet. | |||
| Weighing cell | A mechanical-electrical transducer that converts the force (weight) exerted by the mass of an object into a signal which is uniquely allocated to that particular force. | |||
| Weighing performance | In terms of metrology: Determination of errors of measurement (of a weighing instrument). (See “error of measurement”.) In accordance with verification requirements, weights used to test the weighing performance of an instrument may not deviate by more than 1/3 from the maximum permissible errors of this instrument. | |||
| Window range | Small weighing range, not starting at zero. See “mass comparator”. | |||
| Zero-setting device | Device for zeroing the digital display or analog indicator when the weighing pan is unloaded. On laboratory balances, the zero-setting key function is usually implemented in the tare key. | |||
| Zero-tracking device | Device for maintaining the zero readout of a weighing instrument, within certain limits, automatically. The unofficial term is “auto zero” or “autotaring”. Generally, on laboratory balances, zero tracking is performed even when the balance is tared while a load is on the weighing pan. As a rule, zero tracking can be turned off for certain applications (e.g. for measuring the smallest quantities added or for measuring evaporation from zero). |
