Clinometers for Structural Engineering

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: 0.001 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 • 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: 0-45 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 VDC @7mA • 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) DC input Servo Amp Electronics • 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 0.000006 inch/foot • Hysteresis less than 0.0005% of full range • Many angular accelerometers are based on the same priciple. 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.