1. Clinometers for Structural Engineering
CEE 398
Ping Gu
University of Illinois

2. Outline: Application and Classification Optical Inclinometer
Mechanical Inclinometer
Electrical Inclinometer
Capacitive Accustar
Inductive RVDT
Resistive RPS and Applied Mechanics’s tiltmeter
Special Issue: Clinometers for dynamic testing
RVDT
Clino2000
Force Balance Inclinometers

3. Application and Classification
Application: Clinometers are also called inclinometers, tiltmeters.
the performance of structures under loads, such as curvature of beams and plates
the effects of excavation and tunneling on existing structures
the rotation of dams, piles, retaining walls, struts, anchors,pipelines
road grading and paving
pipeline leveling
crane overturning-moment alarms
Classification
according to reference-system:
gravity referenced: angle w.r.t. vertical gravity vector
locally referenced: angle w.r.t its housing
according to principle:
Optical
Mechanical
Electrical

4. Optical Inclinometer 360 degree range
1 sec reading, estimations to 0.2”
use bubble
Static only
single reading

5. Mechanical Inclinometer
Coincidence Lever
bubble
screw
accuracy: 0.25 sec
sigle reading by eye, static only
Pendulum Clinometer
pendulum
gravity referenced
accuracy: 1min 30 sec
single reading by eye, static only

6. Electrical Inclinometer
Capacitive:
AccuStar
Clino2000
Inductive: RVDT
Resistive:
RPS
Applied Mechanics’s tiltmeter
Other types, such as strain-gage transducers, force balance inclinometers

7. AccuStar Size: 2.6” in diameter 1.2” in height Weight: 20 oz
Total range: +/- 60 degree
Linear range: +/- 45 degree
Resolution: degree
Linearity: +/- 0.1 degree in 10°
Temperature range: -30~65C
Output: digital pulse width; serial data; ratiometric; analog
Price: $139
Capacitor plate
in two halves
etched to form two variable capacitors
dielectric liquid and inert gas
half-filled

8. RVDT Principal: similar to LVDT Range: ± 20 degree
two primary coils and two secondary coils
wound symmetrically on a large-diameter insulated robbin
magnetic cardioid-shaped rotor
mutual inductance varies and produces an output
Range: ± 20 degree
Linearity: ±0.5% ~ ±1.0% fsd
Size: 38.1mm in diameter, 40mm in height
Weight: 250g
Supply voltage: 3V ac to 30V ac
Can be used for dynamic testing
Advantages and disadvantages: similar to LVDT (see my file Potentiometers)
Locally referenced

9. RPS (Rotary Position Sensors)
Principal: similar to POT, except that the wires are wound on a cylindrically shaped core.
IT9101: magnetically-damped pendulum; conductive plastic film
Range: degree
Resolution: essentially infinite
Accuracy: ±2.0% full stroke
Size: 5 inches in diameter, 3.73 inches in thickness Weight: 11 lb
Supply voltage: 30V AC or DC
Can not be used for dynamic testing, but can withstand up to 10g to 2000Hz environmental shock with its added damping
Advantages and disadvantages: similar to POT (see my file Potentiometers)
Locally referenced

10. Applied Mechanics’s tiltmeter
Resistive, gravity referenced
Principle:
Size: 2x2x0.64 inch Weight: 15 g
Range: ±25º
Resolution: 0.01 microradians (0.0006°)
Linearity: 1% over half span, 2.5% over full span
Supply voltage: +8 to +24
Analogue or digital outputs
Measure rotation in two orthogonal vertical planes
High damping of vibration, being used for dam and earthquake monitoring

11. Special Issue: Clinometers for Dynamic Testing
RVDT
Clino 2000
Priciple:
pendulum suspended by the Archimedes helical spring, between two electrodes
pendulum swing, changing the capacity between the pendulum and the two electrodes
RC-oscillator transforms capacities into different frequencies
the ratio of the two frequencies available is used as the primary signal
patent protected in most countries
Price: $2760
Range: ±45°
temperature compensation
Highest possible precision
resolution depends on sampling time
Max error in 24hr for 10° range: 0.055%FS+0.15% RO
integrated DYNAM calculating and displaying static and dynamic inclinations

12. Special Issue: Clinometers for Dynamic Testing (continued)
Force Balance Inclinometers
Principle:
closed-loop torque or force balance servo system
torsional flexure-supported moving mass
servo system electronics
torque motor
feedback sensor
gravity-referenced
Lucas Control Systems
Ranges available: 1° to 90°
Shock survival: 1500g
Vibration endurance-sinusoidal: 50g
Vibration endurance-random: 35g rms, 20 Hz to 2000 Hz
Respond to changes in angle 0.1 sec or slope inch/foot
Hysteresis less than % of full range
Many angular accelerometers are based on the same priciple.
DC input
Servo Amp
Electronics
DC output
Damping
Position sensor
Torque motor
Mass

13. Conclusion: Optical Inclinometer Mechanical Inclinometer
Electrical Inclinometer
Capacitive Accustar Clino2000
Inductive RVDT
Resistive RPS and Applied Mechanics’s tiltmeter
Other types: Force Balance Inclinometers
Those underlined are suitable for dynamic testing
Those bold-faced are locally referenced, others are gravity referenced.