Reliability, Accuracy and Precision

http://en.wikipedia.org/wiki/Accuracy_and_precision

As a start I will define Accuracy & precision from course I have

Accuracy

Accuracy indicates the closeness of the measured value with the actual or true value, and is expressed in the form of the maximum error (= measured value – true value) as a percentage of full scale reading. Thus, if the accuracy of a temperature indicator, with a full scale range of 0-500 ^{oC is specified as ±0.5%, it indicates that the measured value will always be within ±2.5 oC of the true value, if measured through a standard instrument during the process of calibration. But if it indicates a reading of 250 oC, the error will also be ±2.5 oC, i.e. ±1% of the reading. Thus it is always better to choose a scale of measurement where the input is near full-scale value. But the true value is always difficult to get. We use standard calibrated instruments in the laboratory for measuring true value if the variable.}

Precision

Precision indicates the repeatability or reproducibility of an instrument (but does not indicate accuracy). If an instrument is used to measure the same input, but at different instants, spread

over the whole day, successive measurements may vary randomly. The random fluctuations of readings, (mostly with a Gaussian distribution) is often due to random variations of several other factors which have not been taken into account, while measuring the variable. A precision instrument indicates that the successive reading would be very close, or in other words, the standard deviation eσof the set of measurements would be very small. Quantitatively, the precision can be expressed as:

Precision = measured range/σ (5)

The difference between precision and accuracy needs to be understood carefully. Precision means repetition of successive readings, but it does not guarantee accuracy; successive readings may be close to each other, but far from the true value. On the other hand, an accurate instrument has to be precise also, since successive readings must be close to the true value (that is unique).

Can you please elaborate the following statement in the "accuracy" definition pararaph:

" Thus it is always better to choose a scale of measurement where the input is near full-scale value"

i'm not able to relate this to the lines written above in the paragraph

satyendra

this was long definitions from sientific paper so it is long sorry for that but

I had to paste it as it is

now any body can help with reliability and avaliability?

regards

reliability = how dependable

availability = how obtainable

Sweet!

hello!!

Is it possible for you to send me that scientific paper. At least that part which explains how to find accuracy %.

thanks

satyendra

Hi there,

Reliability - The probability that that a device will peform its objective adequately, for the period of time specified, under the operating conditions specified.

Availability - The time that the instrument is needed and able to provide a reading vs the time the instrument is needed and unable to provide a reading.

Regards,

Craig

Please tell me what is "Full scale value" for a instrument such as flue gas analyzer measuring volume % of a gas

satyendra

reliablity------------your girl friend

avaiiablity-----------your wife

accuracy-------If you locate your GF with another guy in discothae

Precision---------Your spectacle you weared that time