1. ECE 3301 General Electrical Engineering
Presentation 08
Voltmeters and Ammeters

2. Analog Multimeter

3. DC Meter Movement
A simple DC ammeter/voltmeter is constructed as shown

4. DC Meter Movement The meter may be modeled as a resistance.
For example, consider a meter that shows a full scale deflection of the pointer when 50 mV is placed across the coil and the resulting current through the coil is 1 mA.
The corresponding resistance is

5. DC Voltmeter
How does one use this meter to measure a maximum of 100 V?

6. DC Voltmeter
Resistance RS is called a “series” resistance.

7. DC Voltmeter
Applying the voltage divider formula to this circuit reveals the equation:

8. DC Voltmeter
Solving the equation for RS

9. DC Voltmeter
Solving the equation for RS

10. DC Voltmeter
Making the numerical substitutions reveals

11. DC Voltmeter
A multiple-range DC voltmeter may be constructed as shown.

12. AC Voltmeter
A multiple-range AC voltmeter may be constructed as shown.

13. DC Ammeter
How does one use this meter to measure 10 Amps?

14. DC Ammeter
RS is called a “shunt” resistance. Applying the current divider formula to this circuit reveals:

15. DC Ammeter
Solving the equation for RS:

16. DC Ammeter
Solving the equation for RS:

17. DC Ammeter
Substituting the numerical values:

18. DC Ammeter
A multiple-range Ammeter may be constructed:

19. Ohmmeter
An Ohmmeter may be constructed as follows :