Instrument error
Encyclopedia
Instrument error refers to the combined accuracy and precision
of a measuring instrument
, or the difference between the actual value and the value indicated by the instrument (error
). Measuring instruments are usually calibrated
on some regular frequency against a standard
. The most rigorous standard is one maintained by a standards organization
such as NIST in the United States
, or the ISO
in Europe
an countries. However, in physics—precision, accuracy, and error are computed based upon the instrument and the measurement data. Precision is to 1/2 of the granularity of the instrument's measurement capability. Precision is limited to the number of significant digits of measuring capability of the coarsest instrument or constant in a sequence of measurements and computations. Error is ± the granularity of the instrument's measurement capability. Error magnitudes are also added together when making multiple measurements for calculating a certain quantity. When making a calculation from a measurement to a specific number of significant digits, rounding (if needed) must be done properly. Accuracy might be determined by making multiple measurements of the same thing with the same instrument, and then calculating the result with a certain
type of math function, or it might mean for example, a five pound weight could be measured on a scale and then the difference between five pounds and the measured weight could be the accuracy. The second definition makes accuracy related to calibration, while the first definition does not.
, that can't be removed. Sometimes the removal of instrument errors are very easy, but it is case dependent. In Engineering instruments, like voltmeter
or ammeter
for example, the instrument error is very difficult to remove. Ammeter has built in resistance, which can't be removed either way. So the only way is to minimize it. On the other hand, the removal of error of a thermometer is a bit simple. Only the calibration has to be removed and then again calibrate it carefully.
Sometimes, the user doesn't care for removal of error from the instrument, else he compensates it in calculation, for example, the zero error in Vernier Caliper
is eliminated by proper calculation.
Another way to deal with instrument error may be to reduce the reactivity
of the system to being measured by using some sort of Weak measurement
. That is, taking far more, but far less powerful readings to avoid changing the system by the act of measuring.
Accuracy and precision
In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which...
of a measuring instrument
Measuring instrument
In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...
, or the difference between the actual value and the value indicated by the instrument (error
Error
The word error entails different meanings and usages relative to how it is conceptually applied. The concrete meaning of the Latin word "error" is "wandering" or "straying". Unlike an illusion, an error or a mistake can sometimes be dispelled through knowledge...
). Measuring instruments are usually calibrated
Calibration
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....
on some regular frequency against a standard
Frequency standard
A frequency standard is a stable oscillator used for frequency calibration or reference. A frequency standard generates a fundamental frequency with a high degree of accuracy and precision. Harmonics of this fundamental frequency are used to provide reference points.Since time is the reciprocal of...
. The most rigorous standard is one maintained by a standards organization
Standards organization
A standards organization, standards body, standards developing organization , or standards setting organization is any organization whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise producing technical standards that are...
such as NIST in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, or the ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
an countries. However, in physics—precision, accuracy, and error are computed based upon the instrument and the measurement data. Precision is to 1/2 of the granularity of the instrument's measurement capability. Precision is limited to the number of significant digits of measuring capability of the coarsest instrument or constant in a sequence of measurements and computations. Error is ± the granularity of the instrument's measurement capability. Error magnitudes are also added together when making multiple measurements for calculating a certain quantity. When making a calculation from a measurement to a specific number of significant digits, rounding (if needed) must be done properly. Accuracy might be determined by making multiple measurements of the same thing with the same instrument, and then calculating the result with a certain
type of math function, or it might mean for example, a five pound weight could be measured on a scale and then the difference between five pounds and the measured weight could be the accuracy. The second definition makes accuracy related to calibration, while the first definition does not.
Removing Instrument Error
The instrument error is not like random errorRandom error
Random errors are errors in measurement that lead to measurable values being inconsistent when repeated measures of a constant attribute or quantity are taken...
, that can't be removed. Sometimes the removal of instrument errors are very easy, but it is case dependent. In Engineering instruments, like voltmeter
Voltmeter
A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to...
or ammeter
Ammeter
An ammeter is a measuring instrument used to measure the electric current in a circuit. Electric currents are measured in amperes , hence the name. Instruments used to measure smaller currents, in the milliampere or microampere range, are designated as milliammeters or microammeters...
for example, the instrument error is very difficult to remove. Ammeter has built in resistance, which can't be removed either way. So the only way is to minimize it. On the other hand, the removal of error of a thermometer is a bit simple. Only the calibration has to be removed and then again calibrate it carefully.
Sometimes, the user doesn't care for removal of error from the instrument, else he compensates it in calculation, for example, the zero error in Vernier Caliper
Caliper
A caliper is a device used to measure the distance between two opposing sides of an object. A caliper can be as simple as a compass with inward or outward-facing points...
is eliminated by proper calculation.
Another way to deal with instrument error may be to reduce the reactivity
Reactivity (psychology)
Reactivity is a phenomenon that occurs when individuals alter their performance or behavior due to the awareness that they are being observed. The change may be positive or negative, and depends on the situation. It is a significant threat to a research study's internal validity and is typically...
of the system to being measured by using some sort of Weak measurement
Weak measurement
Weak measurements are a type of quantum measurement, where the measured system is very weakly coupled to the measuring device. After the measurement the measuring device pointer is shifted by what is called the "weak value". So that a pointer initially pointing at zero before the measurement would...
. That is, taking far more, but far less powerful readings to avoid changing the system by the act of measuring.