Tilt Sensor

The Paris Air show is one of the biggest platforms for various airplane manufacturers to showcase the swiftness of their planes. Some of the valiant pilots of the world perform amazing stunts. These pilots are supported by the power of fast computing machinery in their airplanes. One of the critical parts of this computer assisted circuitry is the tilt sensor. A type of transducer, tilt sensor aids in giving information about the vertical as well as horizontal inclination of the airplane so that the pilot can understand how can he tackle the obstacles during the flight and perform the stunts.

Fig. 1: Image Showing A Typical Tilt Sensor

Keeping the pilots informed about the current orientation of the plane, the angle at which they are inclined to earth’s surface, tilt sensors play a very important role in decision making for the pilots. These types of transducer produce an electric signal proportional to the degree of inclination with respect one or multiple axes. This article will detail more about tilt sensor, the types of tilt sensors, need and their applications. Let’s dig in deep to know about tilt sensors.

Need and Applications of Tilt Sensor

Tilt sensors play a vital role in numerous applications. Diversely popular in multiple fields, tilt sensors are needed in:

· Off Road Vehicles: Off road vehicles such tractors, rock crawling jeeps or tanks are subjected to diverse types of surface terrains. From gravels to sands or marshy areas, these vehicles are expected to perform on every surface. The irregularity and unpredictability of such surfaces is a potential accidental hazard to the vehicle. In the cases when these vehicles are carrying heavy loads, they can tip over or roll down on sudden bumps. Hence, to assist the driver in keeping the vehicle tuned with the surface, tilt sensors play a vital role. In any cases of vertical or horizontal movement of the vehicle, the tilt sensors keep the driver updated so that he knows at which speed he should drive or how he should put the load on the vehicle for safe driving.

· Portable Computers: A popular advertisement about a portable computer says “There is no wrong way or right way you hold the device”. This phrase means that the display of that computer aligns itself in the manner user is holding it and he can tiltit the way he wants. Tilt sensors are required to keep the device display in the correct position with the way user holds it. Often, motion based gaming devices use this application of tilt sensor or tilt sensor derived accelerometer.

· Vehicular Security Systems: Several vehicle security alarm systems are based on tilt sensors. In the cases of unauthorized vehicle towing or movement of steering, tilt sensor engages the alarm. This in turn produces an electric signal and the alarm starts sounding.

· Aviation: In airplanes and helicopters, tilt sensors, along with inclinometers form an altitude monitoring system through which the pilot can monitor the inclinations of the flying machine.

· Robotics: For any type of robot, balance is one of the most important criteria to be taken care of. Whenever a robot inclines to any direction, tilt sensor aids in giving details about corresponding incline in form of electrical signals. It thus makes the robot judge on its own that whether it is supposed to get aligned or not.

A few noteworthy applications of tilt sensors can be seen as under:

Fig. 2: Gaming Controller

1. Gaming Controllers: Popular gaming consoles such as Nintendo Game boy and Game boy Advance used tilt sensing based gaming in some of their cartridges. Later on, 5^th and 6^th generation gaming consoles such as the PlayStation3 and the X-Box360 use tilt sensors as a standard feature in their gaming controllers.

2. Tilted Trains: Tilting trains are those high speed trains running on standard railway tracks. At the points where the track has bends, the trains exert an inertial force to resist the gravitational force. So, whenever a bend in the railway track comes, the trains pull themselves towards the opposite side of the bend. This enables them to continue with their high speed without affecting the comfort of the passengers. Tilt sensors perceive the degree of tilt and convey it to the processing unit. The processing unit generates a signal that aids in maintaining the tilt of the train depending on its speed and the bend of the track. A few popular trains applying this mechanism include Italy’s Pendolino trains, X2 in Sweden and the ICN in Switzerland.

3. Accelerometers: As the name suggests, accelerometers are devices that measure gravitational as well as horizontal motions. They form a critical component of gesture based touch screen devices. Tilt sensors help accelerometers in their response to the gravitational and linear motions. Read more about what is accelerometer and types of accelerometer.

4. Among other devices that are dependent on tilt sensors or are derived from them include tilt meters or inclinometers. The main function of these devices is to measure the degree of tilt and show to the output to the user. Based on the readout, inclinometers can be analog or digital .Electronic power steering in cars is also an application of tilt sensors. The sensors detect the tilt of the steering and combine with the logic unit to steer the vehicle comfortably with less effort from the driver.

Types of Tilt Sensors

Tilt sensors can be broadly classified into two categories: switch based and proportional tilt sensors.

1. Switch Based Tilt Sensors: As the name suggests, these switch sensors answer the question whether the system is tilted or not. With just two states of outputs, switch based sensors are the most basic types. The sensors can be further classified into two types:

a. Mercury Tilt Switch: These switches employ a mercury bead which connects its terminals whenever it is tilted. One of the earliest types, the response of these tilt switches is not quick. Mercury tilt switches can be found in SPST and SPDT form depending upon the number of contacts used in them.

Fig. 3: Mercury Tilt Sensor

As seen from the images above, mercury, being a liquid metal can flow down and establish contact between the leads of the switch. The blob of mercury is able to provide resistance to vibrations as mercury is a dense liquid metal. Using mercury is discouraged as it is a toxic metal and poses a potential hazard to the user when the glass casing breaks and metal spillage take place.

b. Ball in a Cage Structure Switches: These switches are similar to the aforementioned type but employ a metallic ball instead of using mercury. The designing of the ball plays a crucial role as it should not be susceptible to vibrations and shock. Hence, a dense solid structure is used instead of a hollow shell.

Fig. 4: Ball In A Cage Structure Type Tilt Sensor

A pollution free solution to mercury based tilt switches, ball in a cage structures are easy to manufacture too.

As there is no exact measurement of inclination in the switch based sensors, they are often not regarded as sensors by most experts. The sensors that give an output proportional to the tilt are termed as proportional tilt sensors.

Fig. 5: Graphs Comparing Tilt Angle with Output

2. Proportional Tilt Sensors: In these sensors, the output is proportional to the degree of tilt. Proportional tilt sensors are also of various types depending on the tilt mechanism used. Major types of proportional tilt sensors are:

a. Electrolytic Tilt Sensor:

Fig. 6: Electrolytic Tilt Sensor

In this type of sensor, a system of positive-negative electrodes and an electrolyte is there, making it like a lead acid battery. When the sensor is at rest state, electrodes are equally merged in the electrolyte, there is no potential generated. When the sensor gets tilted, the magnitude of submergence of electrodes varies. This results in a potential difference which is dependent on the level of submergence. As shown in the image below, the anode is more submerged in the electrolyte. This will establish a better electrical conductivity between anode and ground.

Fig. 7: Image Showing How An Electrolytic Tilt Sensor Works

Similarly, when the more area of the cathode is submerged, conductivity is higher between it and ground. Corresponding to the submergence is the voltage generated. Since tilting results in resistance change between the terminals, this type of sensor can also be referred to as a potentiometer. This sensor can measure smaller tilt angles and is very accurate in its output. However, its prolonged use can result in a chemical reaction called electrolysis which may render the electrolyte neutral.

Instead of electrolyte, a dielectric liquid can also be used to give a variable capacitor. Detection in capacitance changes due to inclination can also be detected and conditioned to get the desired signal output.

b. MEMS based sensor: The device whose inclination is to be measured can be mounted on a pad containing MEMS sensor. The inclination will be detected by the movement of the object on the sensor. Interestingly, pressure sensors are employed to convey the inclination information.

Fig. 8: Diagrammatic Presentation of How Pressure Sensors Convey Information To MEMS

As seen above, the position of the object on the sensor pad is detected and its respective electrical signal is generated by the sensor. MEMS based sensors are quite sensitive but are not as precise as electrolytic tilt sensors and have a medium resolution. They do provide an option of memory so that previous positions of the object can be recorded. More information about MEMS can be found here.

3. Optical Tilt Sensor: These types of sensors are used in devices such as digital camera or motion based gaming controllers. Preferred for their small size, these sensors detect the intensity of light falling upon them along with the angle that the beam strikes with and give electrical signals accordingly. These sensors employ a light source, detector and at times, lenses.

Optical tilt sensing can be either of switch type or proportional type. In the Switch type mode, there is a source, detector and an obstruction between the two. The obstruction gets moved when the sensor is tilted making the detector receive the light from source and responding accordingly.

Fig. 9: Optical Tilt Sensor

On the other hand, proportional optical tilt sensor employ phase change, diffraction and other principles that varies the output of light resulting in different signal generation.

Another type of optical sensor called optical flow sensor is used in digital cameras to detect the user motion. A camera captures the images of the user and compares the stationary object to the non -stationary ones. Optical flow analysis can be applied on these series of images to detect the user motion and the phone can respond according to that. Such camera based optical flow sensors aid in motion gaming as well as give a better result in photography techniques.

Specification of a Tilt Sensor

A few structural and working configurations form the basis of manufacturing and use of tilt sensors. A few distinct specifications are mentioned below:

1. Number of Axes: The total number of axes upon which the sensor can be expected to respond when actuated is an important factor. While some applications require just a single axis, certain applications such as robotics do require a dual axes tilt sensor. Video game controllers and joysticks are often 3 axes tilt sensor based so that easy movement of the character is there. Some smartphones even employ 4 axes sensors to adjust the display as per the orientation of screen.

2. Resolution: The minimum inclination that can be detected by the sensor is termed as resolution. A good resolution sensor should be able to measure as small inclinations as possible. Electrolytic tilt sensors have a high resolution than the MEMS based ones. For instance, a sensor that can respond to 0.5degree resolution would have a higher resolution that the one which requires a tilt of 1.0degrees.

3. Sensitivity: Another important term is the ability of the sensor to respond to small changes which can be termed as sensitivity. Sensitivity plays a crucial role in those areas where a degree more or less of inclination can make big changes such as in airplanes or high speed trains.

4. Measuring Range: The range of inclination that the sensor can respond to is also a crucial factor. While some sensors are used for a few degree measurements like +/-10, others are required to work at a versatile range of over +/-60.

5. Noise Tolerance: Noise can produce harmonic distortions in the sensor working that might result in output variation and reduce the system efficiency. Noise levels are mentioned by the manufacturer so that the system is accordingly set up.

6. Output: Depending upon the system requirements, the electrical outputs of these sensors can be utilized by the sensors in several manners such as frequency change or even simple current or voltage based indication purposes. Also, output ports can vary as per the system they are used into.

7. Vibration: Similar to noise, vibration is also an undesired factor that has adverse effects on the sensor working. Vibration resistance measures are thus required especially when the sensors are used in harsh conditions like off-road vehicles or construction sites.

8. Other Features: Environmental factors such as humidity and temperature effects, mechanical factors of casing etc also form an important while designing the tilt sensors.

Signal Conditioning

Signal conditioning refers to the manner in which the signal of a sensor is processed so that it can be used further in the system by the logic circuitry or the DSP. Irrespective of the type of sensor used, signal conditioning ought to be carried out in the best of the optimized manners; otherwise the sensor’s output might not give desired results. Some important processes that form integral part of signal conditioning are range matching, filtering, attenuation, amplification, analog to digital conversion etc.

Fig. 10: Diagrammatic Presentation of Signal Conditioning in A Tilt Sensor

As sensors have a wide application, signal conditioning makes the signal just right for the device or the system where sensors are used.

Tilt Sensors are fairly commercialized and are constantly being researched to enhance their working. With wireless tilt sensors already in the market and consumer electronic making wide uses of them, tilt sensors are expected to serve the mankind for long. From huge off roads trailer trucks to small mobile phones, tilt sensor or its derived applications do play a critical role.