Post on 25-Jan-2021
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?