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2.3 Measuring Instruments
Electrical Technology · Grade 10 · 14 lessons in the design
What this covers
- The principle of operation of coil-based (moving-coil) measuring instruments
- Extending range: shunts (for ammeters) and multipliers (for voltmeters)
- Calibrating measuring instruments
- Selecting a suitable scale and range
What you will be able to do
- explain the principle of operation of coil-based measuring instruments
- compute resistance values for shunts and multipliers
- calibrate coil-based measuring instruments
- select a suitable scale for measuring a specified electrical quantity
- recognise the importance of electrical measuring instruments
Key questions
“How does a measuring instrument work?”
“How are measuring instruments calibrated?”
Lessons
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Measuring instruments
40 min · 1 practice tasks · quizHow a coil-based (moving-coil) meter works using electromagnetism, how shunts and multipliers extend its range to make ammeters and voltmeters, how instruments are calibrated, how to select the right scale, and why measuring instruments matter.
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The moving-coil movement
40 min · 1 practice tasks · quizHow a D'Arsonval moving-coil movement turns a tiny current into a pointer reading: magnet, coil, hairspring, linear scale and full-scale deflection.
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Analogue and digital meters
40 min · 1 practice tasks · quizHow a pointer meter differs from a digital meter, when a Kenyan workshop uses each, and which connection rules stay the same.
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The ammeter
40 min · 1 practice tasks · quizWhat an ammeter measures, why it must go in series, why its resistance is very low, and the damage caused by connecting it across a supply.
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Computing a shunt for an ammeter
40 min · 1 practice tasks · quizHow to calculate the shunt resistor that extends a moving-coil movement to a chosen current range, using Ohm's law.
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The voltmeter
40 min · 1 practice tasks · quizWhat a voltmeter measures, why it must go in parallel, why its resistance is very high, and how a Kenya socket is tested.
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Computing a multiplier for a voltmeter
40 min · 1 practice tasks · quizHow to calculate the series multiplier that extends a moving-coil movement to a chosen voltage range.
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The ohmmeter
40 min · 1 practice tasks · quizHow an ohmmeter uses an internal battery to measure resistance, why the analogue scale is reversed, and why the circuit must be dead.
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The multimeter
40 min · 1 practice tasks · quizHow one instrument combines voltmeter, ammeter and ohmmeter: function switch, COM and V/ohm sockets, the 10 A socket, and Kenyan workshop practice.
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Selecting a suitable scale and range
40 min · 1 practice tasks · quizHow to choose a meter range so the reading is accurate: start high, aim for the upper part of the scale, and match AC/DC to the quantity.
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Connecting meters in the workshop
40 min · 1 practice tasks · quizA Kenyan workshop procedure: isolate, choose function and range, connect A in series or V in parallel, keep ohms dead, and never short a socket with the 10 A leads.
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Calibrating coil-based instruments
40 min · 1 practice tasks · quizHow to calibrate a moving-coil meter: mechanical zero, compare with a standard, fine-tune full-scale, verify other points, and why honest calibration is a value.
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Measuring voltage, current and resistance
40 min · 1 practice tasks · quizA bench practical: measure V and I on a 12 V lamp with calibrated meters, compute R, then check R with an ohmmeter on the disconnected lamp.
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Why measuring instruments matter
40 min · 1 practice tasks · quizElectricity is invisible: meters let Kenyan technicians test, find faults, set up equipment and work safely. Honest, calibrated readings are a professional value.