Series 200: Electrical Systems

Course 204.1: Electrical Measuring Instruments

Covers the principles on which electrical test instruments operate. Basic instruments covered include voltmeter, ammeter, wattmeter, ohmmeter, and megohmmeter. Covers AC metering, split-core ammeter, use of current and potential transformers. Includes detailed coverage of modern multimeters. Explains functions and uses of oscilloscopes.

Lesson 1 - Principles of Meter Operation

Topics:

Digital meter design; Integrated ADCs; Displays; Introduction to analog meters; D'Arsonval movement; Magnetic shielding; Parallax error; Accuracy

Learning Objectives:

• Define the terms digital meter and analog meter.
• Describe the purpose of the analog-to-digital converter in a digital meter.
• Identify and label graphs of integrator output from a dual-slope integrating meter.
• Explain how time is related to voltage measurement in an integrating digital meter.
• Differentiate among the terms accuracy, sensitivity, and resolution.
• Explain how a D'Arsonval meter movement works.
• Describe the parallax effect, and explain how to avoid it when using an analog meter.
• State the sensitivity formula for an analog meter.

Lesson 2 - Ammeters, Voltmeters, and Wattmeters

Topics:

Measurement considerations; Measuring direct current; Multirange ammeters; Measuring alternating current; Voltmeters; Wattmeters

Learning Objectives:

• Describe the differences and similarities between an analog ammeter and a voltmeter.
• Explain how ammeters and voltmeters are protected internally from overcurrent.
• Explain how a make-then-break switch works.
• Identify which meters should be connected in series in a circuit and which should be connected in parallel.
• Describe how an analog wattmeter works.
• Explain how it is possible to overload a wattmeter, even with the meter's pointer at less than full-scale deflection.

Lesson 3 - Resistance Measurement

Topics:

Measuring resistance with an ohmmeter; Checking and calibrating an ohmmeter; Shunt ohmmeters; Megohmmeters

Learning Objectives:

• characteristic differences between a series ohmmeter and a shunt ohmmeter.
• Explain why ohmmeter scales read from right to left, instead of left to right, and why they are nonlinear.
• Describe the internal circuits and basic operation of an opposed-coil megohmmeter.
• State the primary safety precaution to take when using an ohmmeter.
• Describe two methods used by ohmmeter manufacturers to extend the range of their instruments.
• Explain how to test for opens, shorts, and grounds, using a megohmmeter.
• Describe how to make zero-adjustments on ohmmeters and megohmmeters.
• Explain why variable resistors are needed in battery-powered ohmmeters.

Lesson 4 - Multimeters

Topics:

Graphical DMM; Advanced meter functions; Multimeter accessories and safety

Learning Objectives:

• Demonstrate how to measure ac and dc current and voltage with a multimeter.
• Describe the function of a current probe.
• Explain how to isolate the source of a glitch with a graphical multimeter.
• Demonstrate how to read the screen display of a graphical multimeter in the Trend mode.
• Explain why you set a meter to its highest range before taking your first measurement.
• Define autoranging and auto-polarity.
• List three safety precautions to take when using multimeters.

Lesson 5 - Oscilloscopes

Topics:

Kinds of oscilloscopes; Triggering; Digital oscilloscopes; Dual-trace oscilloscopes; Controls; Probes; Oscilloscopes in troubleshooting

Learning Objectives:

• Describe how an analog oscilloscope works.
• Describe advantages of a digital oscilloscope over an analog oscilloscope.
• Demonstrate how to measure voltage with an oscilloscope.
• Show two methods of determining phase angles with an oscilloscope.