Pre-Instrument Measurements

The Upper Third Of The Scale:

Before performing measurements, ensure that the instrument is suitable for the range of values in question. Switch on the instrument and check that the reading is 0 in the absence of a measurement signal. (In the case of an ohmmeter, the reading should be infinity; however, the instrument should indicate 0 when the test leads are shorted.)

Ensure that the instrument is not placed near equipment generating a strong magnetic field The test leads and terminals should be in good condition. These items should also be of a type made or recommended by the instrument manufacturer.

If the instrument is equipped with a range selector, commence measurement at the highest setting and work downwards until the correct range is reached. The aim should be to obtain a reading in the upper third of the scale.

Analogue Instrument:

Analogue instruments, in particular, are sensitive to the angle at which the scale is inclined when taking readings, otherwise the friction of the indicator bearing may give rise to inaccuracy. The correct orientation is shown by a marking on the instrument face.

|---| indicates that the scale should be horizontal, __/__ that it should be inclined and __|__ that it should be vertical.





When reading an analogue instrument, the eye should be positioned directly in front of the indicator to eliminate parallax errors.