1. Basic Measuring Instruments

2. * There are 3 types of instruments we use in 50A: * Ammeter * Voltmeter * Ohmmeter

3. * To understand loading effects * To understand a practical use for series and parallel circuits * To what you are doing when you use them

5. Ammeter

9. * When you turn the knob to change scales on an ammeter, you are changing the shunt resistor. Ammeter

12. * AN IDEAL AMMETER HAS 0 OHMS OF INTERNAL RESISTANCE!! * Since no ammeter is perfect, the result is called loading effects.

14. Voltmeter What about Voltmeters?

15. Voltmeter

17. Multi-range Voltmeter

18. * AN IDEAL VOLTMETER HAS ∞ OHMS OF INTERNAL RESISTANCE!! * Since no voltmeter is perfect, the result is called loading effects.

19. Multi-range Voltmeter Voltmeter sensitivity is expressed in ohms/volt (Ω/V). A voltmeter is considered more sensitive if it draws less current from the circuit. The sensitivity of a voltmeter that draws 50uA is the inverse of this, 20,000 ohm per volt.

20. Multi-range Voltmeter

21. * The internal resistance of our DMM is always 10MΩ no matter range is selected. (That’s because there is no range to select.

22. 51.3V 48.7V 95.2kΩ

23. What about Ohmmeters?

25. Ammeter