Definition
An Inclinometer (or Clinometer) is an instrument for measuring angles of slope (or tilt), elevation or inclination of an object with respect to gravity. Also known as a tilt sensor, tilt indicator, slope meter, slope gauge, gradient meter, gradiometer, level gauge & level meter. They are transducers that can resolve as little as 0.1 arc seconds and are available from a variety of manufacturers.
Most DC accelerometers (having a linear response down to 0 Hz) with a reasonably high sensitivity (> 200 mV/g) can be used as inclinometers. Because they have a DC response, these types of accelerometers can measure constant, or static, accelerations like gravity. When their axes of sensitivity are aligned with the direction of gravity, they output a voltage proportional to 1 g (9.807 m/s2) of acceleration.
Some confusion may arise as some geo-science experts classify inclinometers as:
Inclinometers, also known as slope inclinometers, probe inclinometers and slope indicators, these are devices for monitoring deformation normal to the axis of a pipe, by means of a probe passing along the pipe. The pipe can be horizontal, vertical or inclined and will have four grooves along its length to act as a guide for the inclinometer probe wheels.
Construction
An inclinometer puts out an electronic signal proportional to the angle of tilt, relative to level. Internally, the inclinometer consists of a tilt sensor and signal-conditioning electronics. These normally reside in one enclosure with either a cable or connector as output.
Fig 1. Electrolytic fluid-filled tilt sensor inclinometer
The most commonly used tilt sensor in inclinometers is an electrolytic fluid-filled type. Electrolytic tilt sensors need an ac excitation voltage and deliver an ac output voltage. The signal-conditioning electronics generate the ac excitation and subsequently demodulate the ac-voltage output. The sensors work in an ac Wheatstone bridge. At null or level, sensors produce a signal equal to 50% of the total scale factor or output setting. With angular movement in either direction, this ratio changes proportionally. Typical construction uses a ceramic container filled with an electrical conductive fluid and two platinum electrodes measure the electronic conductivity.
In other construction scheme the movement of a damped electrolytic fluid in a narrow channel allows a miniature device to precisely measure angles with respect to Earth's gravity vector. This inclinometer is capable of measuring angles over the full 360 degrees of rotation, while resolution is maintained at less than ± 0.01 degrees. The sensor is also inherently immune to cross-axis rotations and linear translations.
A full 360° range absolute tilt sensing programmable level device with either digital or analog output is constructed as follow: internally, a rotary bar coded disk is mounted to a weighted gravity driven wheel. A micro-controller strobes a LED to transfer the bar code image onto an optical linear array, then it decodes the position every 4mSec. Magnetic damping provides fast response and settling time while virtually eliminating overshoot and oscillations. An internal EEPROM stores field programmable parameters such as resolution, zero position, direction swap, and mode. This second generation design virtually eliminates the primary accuracy limitation of first generation inclinometers, which is sitation (hysteresis).
On another construction schema, the force-balance closed-loop configuration, overcomes most of the open-loop mass-and-spring inclinometer errors, as well as the speed limitation. Because the spring’s only function is to suspend and guide the mass, it is designed to be as weak as possible, and its restoring force is replaced by an electromagnetic balancing force. As the mass begins to move under the gravitational force, the coil applies an opposing force proportional to tilt, which tracks the deflection (negative feedback); the mass movement will stop as the forces balance each other.
By combining a pair of DC accelerometers with a 12 bit A/D, mux, microcontroller, and D/A converter to provide an analog voltage linearly proportional to inclination a manufacturer of inclinometers also has included an onboard user programmable infinite impulse response (IIR) digital filter.
Other manufacturer uses capacitance-based sensors for the precise measurement of level, angle or tilt. This designs feature a wide range of performance parameters, interface options and price alternatives. These rugged sensors can withstand high levels of shock and vibration that might destroy a MEMS-type device. They also have very high accuracy, especially around zero degrees, which makes them ideal for leveling applications. Physically the sensor is composed of two hermetically sealed domes spaced about 1/8" apart. The lower, polyester plastic dome has 4 capacitive plates while the aluminum, upper dome acts as a ground. A fluid with a high dielectric constant is sealed within the dome sandwich, leaving an air bubble space about the size of a quarter. The bubble is centered at level position and will move from one side to the other as the device is tilted.
On some inclination sensors the x- and y- axis can be evaluated independently from each other. Latest models integrate a micro-controller for rapid measuring and processing of the angle. In order to adapt the inclination sensor to the requirements of the application, several device parameters may be available to the user and can be programmable.
Applications
Inclination sensors are used for horizontal leveling of machines, as well as for controlling of earthmovers, propulsion devices and special-purpose vehicles.
One-axis inclinometers provide only longitudinal slope axis value. Two-axis inclinometers provide additionally lateral slope axis value.
Cranes and boom lifts use inclinometers for sensing boom angle. Road graders and pavers use them for controlling blade angle. Crawler drills used in the mining industry use inclinometers to monitor and control the drill mast angle. Other applications are as diverse as wheel-alignment systems and vehicle/platform leveling and monitoring.
Mobile antenna platforms are another application. These systems must precisely align with the satellite they track. Small positional-pointing errors of the antenna can severely degrade signal strength and quality. Errors of a fraction of a degree can be deleterious. So satellite antenna-positioning systems rely on the accuracy of sensors giving positional feedback.
On the military and aerospace industries the single-axis version has been used in tank fire-control systems, in which it demonstrated accuracy down to a few arc-seconds under repeated shocks of thousands of g’s, vibration, and temperature extremes. Inclinometers are currently being considered for leveling the transporters used by NASA to carry spacecraft to the launching pad. The dual-axis model is being used as a horizontal reference for the radar antenna of the Arrow anti-missile systems, where a 0.0028° accuracy over the full temperature range and over a period of years is required.
Low-range MEMS accelerometers could be used for less demanding leveling and low-range tilt measurement. One application used a MEMS accelerometer mounted on a simple rotary device to level diamond-polishing tables, achieving an order of magnitude accuracy improvement.
Inclinometers could also find applications in laboratories and other test setups that require accuracy and repeatability of single-digit arc-seconds over long periods of time. Inclinometers do a great job on installations in which the device is hard or impossible to reach for calibration purposes, such as under water, under ground, high altitudes, or remote locations.
Finally, sensors are rough enough to be used on equipment working under extreme environmental conditions (e.g., variable temperatures, high-level shock and vibration).
Applications on:
vehicles, platforms, construction equipment, heavy equipment
vehicle testing, car alarms, tip-over protection, roll prevention, static and dynamic leveling
computer science, biomedical, aerospace and robotics.
animation, linkage free tracking, control
civil engineering
structural deflections, geo-mechanics
antenna installations
antenna positioning, aiming optimization, dynamic correction
manufacturing
container handling, hydraulic lift systems, machine tools.
