*
Basic Measuring
Instruments
*There are 3 types of instruments we use in 50A:
*Ammeter
*Voltmeter
*Ohmmeter
*
*
*To understand loading effects
*To understand a practical use for series and
parallel circuits
*To what you are doing when you use them
*
Ammeter
*
*
*
Ammeter
*
*
Ammeter
*
*
*
Ammeter
*
*
*
Ammeter
* When you turn the knob to
change scales on an ammeter,
you are changing the shunt
resistor.
*
*
*
*
*
*
*
*
*
*
* AN IDEAL AMMETER HAS 0 OHMS OF
INTERNAL RESISTANCE!!
* Since no ammeter is perfect, the
result is called loading effects.
*
http://www.youtube.
com/watch?v=lkwh4Z
axHIA&feature=email
What about Voltmeters?
Voltmeter
*
*
*
*
Voltmeter
*
Voltmeter
*
*
*
Multi-range Voltmeter
*
*
*
*
*
*
*
* AN IDEAL VOLTMETER HAS ∞ OHMS OF
INTERNAL RESISTANCE!!
* Since no voltmeter is perfect, the
result is called loading effects.
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.
*
*
*
voltmeter sensitivity
Multi-range Voltmeter
*
*
Multi-range Voltmeter
*
*
* The internal resistance of our DMM is
always 10MΩ no matter range is selected.
(That’s because there is no range to select.
*
51.3V
95.2kΩ
*
*
*
*
*
*
Loading Effects
48.7V
What about Ohmmeters?
*
What about Ohmmeters?
*
*
What about Ohmmeters?
Ammeter
*
*