Understanding of Introductory Concepts of Measurement and Testing and the Meaning of Related Terms and Expressions

Q1.Distinguish between measurement and testing

A1.Measurement is defined as the collection of data, the values of certain variables such as resistance, voltage and current may be found at certain points in a circuit or system. These values are obtained using relevant measurement instruments and techniques.

Testing is defined as manipulating the values gained during the measurement phase described above to determine whether or not a circuit or system under test is operating correctly or at maximum efficiency.

Q2.Explain the meaning of resolution and indicate what determines it for an analogue and for a digital measuring device.

A2.Resolution is defined as the magnitude of signal equivalent to one count of the least significant digit of the display. This means the smallest signal strength that it is possible to measure. For a digital device the resolution is determined by the number of digits after the decimal point on a particular range. For an analogue device resolution is determined by the width of the needle and the space between adjacent graticules on the display.

Q3.Distinguish between accuracy and sensitivity of an instrument, quote examples of typical figures for analogue and digital meters

A3.Accuracy is the limit, usually expressed as a percentage of full scale deflection (FSD) not exceeded by errors when the instrument is under reference conditions ie if the accuracy of a certain device is 1% of FSD between certain temperatures, if the device if used between those temperatures to measure voltages on a 10V range, the maximum difference between the voltage being measured and that displayed should be 1% of 10V (0.1V). The accuracy figure is required as no instrument will ever be perfectly accurate.

Typical accuracy for a digital device is +/- 0.1V + 2LSD (Least Significant Digit).

Typical accuracy for an analogue device is +/- 2.5% FSD.

Usually quoted...