“indicator”的概念、定义、翻译、参考文献-科学参考

indicator

Chemistry

A substance used to show the presence of a chemical substance or ion by its colour. Acid–base indicators are compounds, such as phenolphthalein and methyl orange, that change colour reversibly, depending on whether the solution is acidic or basic. They are usually weak acids in which the un-ionized form HA has a different colour from the negative ion A⁻. In solution the indicator dissociates slightly
$HA ⇌ H^{+} {+ A}^{-}$
In acid solution the concentration of H⁺ is high, and the indicator is largely undissociated HA; in alkaline solutions the equilibrium is displaced to the right and A⁻ is formed. Useful acid–base indicators show a sharp colour change over a range of about 2 pH units. In titration, the point at which the reaction is complete is the equivalence point (i.e. the point at which equivalent quantities of acid and base are added). The end point is the point at which the indicator just changes colour. For accuracy, the two must be the same. During a titration the pH changes sharply close to the equivalence point, and the indicator used must change colour over the same range.
Other types of indicator can be used for other reactions. Starch, for example, is used in iodine titrations because of the deep blue complex it forms. Oxidation-reduction indicators are substances that show a reversible colour change between oxidized and reduced forms. See also adsorption indicator.

Chemical Engineering

1. A substance that indicates the completion of a chemical reaction. It is often used to determine the end point in titrations, and involves a sharp colour change.

2. A type of process controller that provides measures and controls a process variable such as temperature. On a piping and instrumentation diagram a TIC is a temperature indicator controller while a LIC is a level indicator controller.

Computer

1. A bit or bit configuration that may be inspected to determine a status or condition. Examples are an overflow bit, a device status, any portion of the program status word. See also qualifier register.
2. A visual, sometimes aural, indication of the occurrence of a specific status or condition, e.g. system running (halted), undefined instruction.

Geology and Earth Sciences

See erratic.

Economics

A variable used to determine the employment of policy instruments. An indicator is used to show when a policy should be introduced, or when the level of an existing policy instrument should be changed. Policy indicators are distinguished from both targets and instruments. Economic policy targets include objectives such as high levels of employment and growth, low and stable levels of inflation, or maintenance of particular exchange rates. Policy instruments are variables the government or central bank can control, or at least influence, such as tax rates or the money supply. Policy indicators may themselves be targets, but frequently are not. They are preferred to targets for use in decision-making because they are available sooner or can be measured more reliably than targets. Policy instruments cannot be indicators for the authority that decides them, but where decision-making is decentralized, one authority’s instrument may be used as another’s indicator. See also economic indicators; leading indicator.

单词	indicator
释义	indicator Chemistry A substance used to show the presence of a chemical substance or ion by its colour. Acid–base indicators are compounds, such as phenolphthalein and methyl orange, that change colour reversibly, depending on whether the solution is acidic or basic. They are usually weak acids in which the un-ionized form HA has a different colour from the negative ion A⁻. In solution the indicator dissociates slightly $HA ⇌ H^{+} {+ A}^{-}$ In acid solution the concentration of H⁺ is high, and the indicator is largely undissociated HA; in alkaline solutions the equilibrium is displaced to the right and A⁻ is formed. Useful acid–base indicators show a sharp colour change over a range of about 2 pH units. In titration, the point at which the reaction is complete is the equivalence point (i.e. the point at which equivalent quantities of acid and base are added). The end point is the point at which the indicator just changes colour. For accuracy, the two must be the same. During a titration the pH changes sharply close to the equivalence point, and the indicator used must change colour over the same range. Other types of indicator can be used for other reactions. Starch, for example, is used in iodine titrations because of the deep blue complex it forms. Oxidation-reduction indicators are substances that show a reversible colour change between oxidized and reduced forms. See also adsorption indicator. Chemical Engineering 1. A substance that indicates the completion of a chemical reaction. It is often used to determine the end point in titrations, and involves a sharp colour change. 2. A type of process controller that provides measures and controls a process variable such as temperature. On a piping and instrumentation diagram a TIC is a temperature indicator controller while a LIC is a level indicator controller. Computer 1. A bit or bit configuration that may be inspected to determine a status or condition. Examples are an overflow bit, a device status, any portion of the program status word. See also qualifier register. 2. A visual, sometimes aural, indication of the occurrence of a specific status or condition, e.g. system running (halted), undefined instruction. Geology and Earth Sciences See erratic. Economics A variable used to determine the employment of policy instruments. An indicator is used to show when a policy should be introduced, or when the level of an existing policy instrument should be changed. Policy indicators are distinguished from both targets and instruments. Economic policy targets include objectives such as high levels of employment and growth, low and stable levels of inflation, or maintenance of particular exchange rates. Policy instruments are variables the government or central bank can control, or at least influence, such as tax rates or the money supply. Policy indicators may themselves be targets, but frequently are not. They are preferred to targets for use in decision-making because they are available sooner or can be measured more reliably than targets. Policy instruments cannot be indicators for the authority that decides them, but where decision-making is decentralized, one authority’s instrument may be used as another’s indicator. See also economic indicators; leading indicator.
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