Agilent Technologies U8001A Specifications download pdf (Page 33)

Instrumentation Laboratory Exercise 30

Laboratory Exercise 4

Foto-optic measurements of speed and flicker

Apparatus

• One 10 kΩ Resistor

• One Cadmium Disulphide (CdS) fotoresistor

• 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

4.1 Introduction

The purpose of this laboratory exercise is to measure the frequency

response of the Cadmium Disulphide (CdS) fotoresistor, and to

measure the flicker frequency of fluorescent lights. The CdS cell is an

inexpensive light sensitive resistor. Its resistance may be on the order

of 100 Ω when fully illuminated, and as high as 100,000 Ω in

darkness.

The CdS cell will be mounted below the holes of the motor's disk. As

the motor spins the opaque portions of the index wheel will shield

the CdS cell from light, changing its resistance, and producing a

measurable voltage. This voltage will be measured (peak- to- peak) as

the motor speed is changed. The amplitude will be displayed on the

computer, along with the raw signal.

As the motor speed is increased the frequency increases, and the

amplitude of the signal will decrease due to the low- frequency nature

of CdS cells. You should measure the maximum reasonable frequency

(at which the amplitude is equal to 50% of the DC amplitude) of the

CdS cell. Finally, the background noise of the florescent light flicker

should be measured.

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Agilent Technologies U8001A Specifications Page 33