Clinometers for Structural Engineering CEE 398 Ping Gu University of Illinois

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

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

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

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

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

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

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

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

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

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

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 0.000006 inch/foot Hysteresis less than 0.0005% 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

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.