Optical Attenuation Sensor forProcess Control

Eric A. Borisch

Jeremy D. Protas

Scott D. Ruppert

Christopher J. Spiek

Francis L. Merat, Advisor

April 21, 1999

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Project Background

Originated by a company in theCleveland area

Robotic binary epoxy sprayer Currently using an optical spectrum analyzer

for process control

Looking for an inexpensive alternative

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Project Goals

Decreased cost

Wide dynamic range

Strong correlation

Stability

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Our Solution

Frequency source Light emitting diode phototransistor

pair Amplify & rectify the detected signal Take the DC value of the AC component

DC OUTPUTLNA AD630

OSCILATOR LED PHOTO-NPN DC BLOCK LOCK-IN LPF

REFERENCE SIGNAL

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Design Considerations

Oscillator design

Optical transmission and detection

Attenuation measurement

Output

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Oscillator Design

Onboard

Sine wave orsquare wave

Wien Bridgeoscillator -6V

+6V

450p 330k

+

- LM741N1.5k

2.7k

50500

330k

450p

Wien Bridge oscillator

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Optical Transmission

High output infraredLED

Separate AC & DCdrive controls

+6V

Q2N3904Q2N3904

10027

1M10k

10k

LED

10mH

AC CONTROL DC OFFSETCONTROL

LED Drive

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Optical Detection

Phototransistorinstead of photodiode

Low noise amplifier

Variable gain

Over-amplificationdetection

-6V

+6V

+

- CLC425

100n

4.7u

PHOTO NPN1

51

2n

100k

100n

4.7u

JP3JP2JP1

51 510 5.1k 51k

AMPLIFICATION JUMPERS

JP4

Photoreceiver/Amplifier

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Attenuation Measurement

AD630 - Lock-in amplifier

Reference & received signals compared

Low pass filter

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Output

DC value

Output circuit Adjustable set points

Easy to read

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Results

Over 50 dB dynamic range

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

ResultsOutput Voltage

0

100

200

300

400

500

600

700

800

900

1000

0.00001% 0.00010% 0.00100% 0.01000% 0.10000% 1.00000% 10.00000% 100.00000%

Transmission

Vo

ltag

e (m

V)

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Results

Over 50 dB Dynamic Range

DC output linearly correlated with opticalattenuation

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

ResultsLow Amplification

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Transmission %

Ou

tpu

t (V

)

50 Ohm

FIT

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Results

Over 50 dB Dynamic Range

DC output linearly correlated with opticalattenuation

Crosstalk

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Results

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Recommendations

Better sine wave oscillator

Auto-ranging or application specific

Packaged for industrial environment

Multiple circuits with neural network

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Demonstration

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Conclusions

Goals Decreased cost

Wide dynamic range

Strong correlation

Stability

Results Under $50

Over 50 dB

Repeatability &Linearity

Unaffected byTransients

April 21, 1999 Optical AttenuationSensor for Process Control

EEAP 398/399

Any Questions?