The Philosophy and Consequence of Measurement – Accuracy

The Philosophy and Consequence of Measurement – Accuracy (continued)

Published: 24th February 2014

From our venture into the world of atomic clocks, relativity and possible time travel let’s focus more into accuracy. The quality or state of being correct or precise: technical- the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.

Let’s look at a some typical specifications

Digital Multimeters where accuracy is fundamentally described as ± % of reading. For example, if the basic meter accuracy in the dc volts range is ±1 %, and the true voltage is 1.00 V, the meter is expected to display a reading of 1.00 V ±1 %, or 0.99 V to 1.01 V. However, basic accuracy does not take into account the inner workings of the ADC (tolerances, nonlinearities, offsets etc.) To give meter users a more accurate value, DMM manufacturers present accuracy specifications in the following format:

Complete accuracy specifications: ±(% of reading + number of LSD) Where: Reading = the true value of the signal that the DMM measures and LSD = least significant digit

Oscilloscopes - dc Gain Accuracy, ± 1.25% of full scale. An oscilloscopes accuracy is often specified in terms of gain accuracy and offset accuracy. Gain accuracy is related to how well it handles high-frequency noise and can be called its relative accuracy. Offset accuracy is related to how well it handles the low-frequency issues and can be referred to as absolute accuracy. Accuracy refers to the oscilloscopes ability to represent the true value of a signal. The factors that reduce the accuracy of an oscilloscope can be mostly lumped into high- and low-frequency errors. Noise is generally the cause of high-frequency errors, while low-frequency errors are caused by drift stemming from temperature, aging, bias currents, etc.

Spectrum Analysers and Power Meters (High resolution/accuracy +/- 50 Vdc DVM and associated). The accuracy of a spectrum analyser might not be up to that of a dedicated power meter for example, the accuracy of the individual level measurements need to be accurate to enable useful measurements to be made. The amplitude accuracy specification of a spectrum analyser is determined by a number of factors, including the basic accuracy of the instrument as well as its frequency response. This means that the frequency elements should also be taken into consideration. Some spectrum analysers incorporate a power meter to provide a very accurate measurement specification. For this, the spectrum analyser has a special power sensor that calibrates the input level at a number of absolute level points, then uses the very good linearity of the analyser to very accurately measure levels over the full range.

Signal Generators- RF Level Accuracy. The RF output level accuracy of a signal generator is considered to be a prime specification parameter.

So, wherever you look you will see reference to accuracy and you will consider how that fits into the measurement that you are looking to provide and the decisions you are looking to make. Rejoice in your measurements. Demand more and enjoy this series.

From our venture into the world of atomic clocks, relativity and possible time travel let’s focus more into accuracy. The quality or state of being correct or precise: technical- the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.

Let’s look at a some typical specifications

Digital Multimeters where accuracy is fundamentally described as ± % of reading. For example, if the basic meter accuracy in the dc volts range is ±1 %, and the true voltage is 1.00 V, the meter is expected to display a reading of 1.00 V ±1 %, or 0.99 V to 1.01 V. However, basic accuracy does not take into account the inner workings of the ADC (tolerances, nonlinearities, offsets etc.) To give meter users a more accurate value, DMM manufacturers present accuracy specifications in the following format:

Complete accuracy specifications: ±(% of reading + number of LSD) Where: Reading = the true value of the signal that the DMM measures and LSD = least significant digit

Oscilloscopes - dc Gain Accuracy, ± 1.25% of full scale. An oscilloscopes accuracy is often specified in terms of gain accuracy and offset accuracy. Gain accuracy is related to how well it handles high-frequency noise and can be called its relative accuracy. Offset accuracy is related to how well it handles the low-frequency issues and can be referred to as absolute accuracy. Accuracy refers to the oscilloscopes ability to represent the true value of a signal. The factors that reduce the accuracy of an oscilloscope can be mostly lumped into high- and low-frequency errors. Noise is generally the cause of high-frequency errors, while low-frequency errors are caused by drift stemming from temperature, aging, bias currents, etc.

Spectrum Analysers and Power Meters (High resolution/accuracy +/- 50 Vdc DVM and associated). The accuracy of a spectrum analyser might not be up to that of a dedicated power meter for example, the accuracy of the individual level measurements need to be accurate to enable useful measurements to be made. The amplitude accuracy specification of a spectrum analyser is determined by a number of factors, including the basic accuracy of the instrument as well as its frequency response. This means that the frequency elements should also be taken into consideration. Some spectrum analysers incorporate a power meter to provide a very accurate measurement specification. For this, the spectrum analyser has a special power sensor that calibrates the input level at a number of absolute level points, then uses the very good linearity of the analyser to very accurately measure levels over the full range.

Signal Generators- RF Level Accuracy. The RF output level accuracy of a signal generator is considered to be a prime specification parameter.

So, wherever you look you will see reference to accuracy and you will consider how that fits into the measurement that you are looking to provide and the decisions you are looking to make. Rejoice in your measurements. Demand more and enjoy this series.

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