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Instrumentation Laboratory Exercise 23
Laboratory Exercise 3
Motor current characteristics
Apparatus
• One 0.5 Ω, 5 W resistor
• Small permanent magnet (PM) DC motor
• Test/prototyping board
• Agilent U2351A, U2352A, U2353A, or U2354A USB multifunction
data acquisition device
• Agilent E3620A 50 W dual output power supply or Agilent
U8001A/U8002A single output DC power supply
3.1 Introduction and Objectives
The purpose of this lab is to measure the current (I) versus
voltage (V) characteristics of a permanent magnet DC motor. A small
DC motor will be supplied with power from a variable power supply.
The negative side of the motor will be connected to ground through a
5 W, 0.5 Ω current sense resistor. The voltage of the current sense
resistor and the motor voltage will be read into the DAQ system.
The difference in voltage will be calculated and displayed as the
Motor Voltage. The current sense resistors voltage will be converted
to a current by dividing by the resistance (0.5 Ω). This current will be
displayed as the Motor Current. On a two- dimensional graph, the
current will be plotted as a function of voltage.
The power supply will be set to various voltage levels (2 V, 3 V, and
4 V). Initially the motor will operate at its no- load speed. At each
voltage a frictional break (folded paper pad) will be applied to the
motors output disk, gradually slowing the motor to a stop. The break
should be applied such that it takes several seconds for the motor to
spin to a stop, during which time the motor voltage and current are
recorded and plotted.