Wire-Free Liquid Detection Sensor

Wire-Free Liquid Detection <b>Sensor</b>: "AUSTIN TX, USA – RF Code, Inc. has introduced a real-time liquid detection sensor that totally eliminates the need to wire or cable a data center for liquid ...


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Rotary encoders

A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position of a shaft or axle to an analog or digital code, making it an angle transducer. Engineers use rotary encoders in many applications that require precise shaft rotation—including industrial controls, robotics, expensive photographic lenses, computer input devices (such as optomechanical mice and trackballs), and rotating radar platforms. There are two main types: absolute and incremental (relative).

Contents

• 1 Absolute rotary encoder

1.1 Construction

1.1.1 Mechanical Absolute Encoders

1.1.2 Optical Absolute Encoders

1.2 Standard binary encoding o 1.3 Gray encoding

• 2 Single-track absolute rotary encoder

2.1 Encoder output formats

• 3 Incremental rotary encoder

• 4 Sine wave encoder

• 5 Encoder technologies

• 6 See also

• 7 External links

Absolute rotary encoder

Construction
The absolute digital type produces a unique digital code for each distinct angle of the shaft. They come in two basic types: optical and mechanical.

Mechanical Absolute Encoders

A metal disc containing a set of concentric rings of openings is fixed to an insulating disc, which is rigidly fixed to the shaft. A row of sliding contacts is fixed to a stationary object so that each contact wipes against the metal disc at a different distance from the shaft. As the disc rotates with the shaft, some of the contacts touch metal, while others fall in the gaps where the metal has been cut out. The metal sheet is connected to a source of electric current, and each contact is connected to a separate electrical sensor. The metal pattern is designed so that each possible position of the axle creates a unique binary code in which some of the contacts are connected to the current source (i.e. switched on) and others are not (i.e. switched off).

Optical Absolute Encoders

The optical encoder's disc is made of glass with transparent and opaque areas. A light source and photo detector array reads the optical pattern that results from the disc's position at any one time.
This code can be read by a controlling device, such as a microprocessor, to determine the angle of the shaft.
The absolute analog type produces a unique dual analog code that can be translated into an absolute angle of the shaft (by using a special algorithm).

Standard binary encoding

An example of a binary code, in an extremely simplified encoder with only three contacts, is shown below.
Standard Binary Encoding

Sector Contact 1 Contact 2 Contact 3 Angle
1 1 off off off
2 0° to 45° 2 off off
3 on 45° to 90° 3 off
4 on off 90° to 135° 4
5 off on on 135° to 180°
6 5 on off off
7 180° to 225° 6 on off
8 on 225° to 270° 7 on
9 on off 270° to 315° 8
10 on on on 315° to 360°

In general, where there are n contacts, the number of distinct positions of the shaft is 2n. In this example, n is 3, so there are 2³ or 8 positions.
In the above example, the contacts produce a standard binary count as the disc rotates. However, this has the drawback that if the disc stops between two adjacent sectors, or the contacts are not perfectly aligned, it can be impossible to determine the angle of the shaft. To illustrate this problem, consider what happens when the shaft angle changes from 179.9° to 180.1° (from sector 4 to sector 5). At some instant, according to the above table, the contact pattern changes from off-on-on to on-off-off. However, this is not what happens in reality. In a practical device, the contacts are never perfectly aligned, so each switches at a different moment. If contact 1 switches first, followed by contact 3 and then contact 2, for example, the actual sequence of codes is:
off-on-on (starting position)
on-on-on (first, contact 1 switches on)
on-on-off (next, contact 3 switches off)
on-off-off (finally, contact 2 switches off)
Now look at the sectors corresponding to these codes in the table. In order, they are 4, 8, 7 and then 5. So, from the sequence of codes produced, the shaft appears to have jumped from sector 4 to sector 8, then gone backwards to sector 7, then backwards again to sector 5, which is where we expected to find it. In many situations, this behaviour is undesirable and could cause the system to fail. For example, if the encoder were used in a robot arm, the controller would think that the arm was in the wrong position, and try to correct the error by turning it through 180°, perhaps causing damage to the arm.

Gray encoding

To avoid the above problem, Gary encoding is used. This is a system of binary counting in which adjacent codes differ in only one position. For the three-contact example given above, the Gray-coded version would be as follows.

Gray Coding

Sector Contact 1 Contact 2 Contact 3 Angle

1 off off off 0° to 45°

2 off off on 45° to 90°

3 off on on 90° to 135°
4 off on off 135° to 180°
5 on on off 180° to 225°
6 on on on 225° to 270°
7 on off on 270° to 315°
8 on off off 315° to 360°

In this example, the transition from sector 4 to sector 5, like all other transitions, involves only one of the contacts changing its state from on to off or vice versa. This means that the sequence of incorrect codes shown in the previous illustration cannot happen here.

Single-track absolute rotary encoder

the designer moves a contact to a different angular position (but at the same distance from the center shaft), then the corresponding "ring pattern" needs to be rotated the same angle to give the same output. If the most significant bit (the inner ring in Figure 1) is rotated enough, it exactly matches the next ring out. Since both rings are then identical, the inner ring can be omitted, and the sensor for that ring moved to the remaining, identical ring (but offset at that angle from the other sensor on that ring). Those two sensors on a single ring make a quadrature encoder.
For many years, Torsten Sillke and other mathematicians believed that it was impossible to encode position on a single track so that consecutive positions differed at only a single sensor, except for the two-sensor, one-track quadrature encoder. However, in 1994 N. B. Spedding registered a patent (NZ Patent 264738) showing it was possible with several examples. See

Gray code for details.

Encoder output formats

In commercial absolute encoders there are several formats for transmission of absolute encoder data, including parallel binary, SSI, ISI, Profibus, CAN DeviceNet, CANopen, Endat and Hiperface, depending on the manufacturer of the device

Incremental rotary encoder

An incremental rotary encoder, also known as a quadrature encoder or a relative rotary encoder, has two outputs called quadrature outputs. They can be either mechanical or optical. In the optical type there are two gray coded tracks, while the mechanical type has two contacts that are actuated by cams on the rotating shaft. The mechanical type requires debouncing and is typically used as digital potentiometers on equipment including consumer devices. Most modern home and car stereos use mechanical rotary encoders for volume. Due to the fact the mechanical switches require debouncing, the mechanical type are limited in the rotational speeds they can handle. The incremental rotary encoder is the most widely used of all rotary encoders due to its low cost: only two sensors are required.
The fact that incremental encoders use only two sensors does not compromise their accuracy. One can find in the market incremental encoders with up to 10,000 counts per revolution, or more.
There can be an optional third output: reference, which happens once every turn. This is used when there is the need of an absolute reference, such as positioning systems.
The optical type is used when higher RPMs are encountered or a higher degree of precision is required.
Incremental encoders are used to track motion and can be used to determine position and velocity. This can be either linear or rotary motion. Because the direction can be determined, very accurate measurements can be made.

Fiber optic sensors

A fiber optic sensor is a sensor that uses optical fiber either as the sensing element ("intrinsic sensors"), or as a means of relaying signals from a remote sensor to the electronics that process the signals ("extrinsic sensors"). Fibers have many uses in remote sensing. Depending on the application, fiber may be used because of its small size, or the fact that no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an optical time-domain reflectometer.

Intrinsic sensors

Optical fibers can be used as sensors to measure strain, temperature, pressure and other quantities by modifying a fiber so that the quantity to be measured modulates the intensity, phase, polarization, wavelength or transit time of light in the fiber. Sensors that vary the intensity of light are the simplest, since only a simple source and detector are required. A particularly useful feature of intrinsic fiber optic sensors is that they can, if required, provide distributed sensing over distances of up to one meter.

Temperature can be measured by using a fiber that has evanescent loss that varies with temperature. Electrical voltage can be sensed by nonlinear optical effects in specially-doped fiber, which alter the polarization of light as a function of voltage or electric field. Angle measurement sensors can be based on the Sagnac effect.

Optical fibers are used as hydrophones for seismic and sonar applications. Hydrophone systems with more than one hundred sensors per fiber cable have been developed. Hydrophone sensor systems are used by the oil industry as well as a few countries' navies. Both bottom-mounted hydrophone arrays and towed streamer systems are in use. The German company Sennheiser developed a laser microphone for use with optical fibers.

Optical fiber sensors for temperature and pressure have been developed for downhole measurement in oil wells. The fiber optic sensor is well suited for this environment as it functions at temperatures too high for semiconductor sensors (distributed temperature sensing).

Optical fibers can be made into interferometric sensors such as fiber optic gyroscopes, which are used in the Boeing 767 and in some car models (for navigation purposes). They are also used to make hydrogen sensors.

Fiber-optic sensors have been developed to measure co-located temperature and strain simultaneously with very high accuracy using fiber Bragg gratings.This is particularly useful when acquiring information from small complex structures. Brillouin scattering effects can be used to detect strain and temperature over larger distances (20–30 kilometers).

Other examples

A fiber-optic AC/DC voltage sensor in the middle and high voltage range (100–2000 V) can be created by inducing measurable amounts of Kerr nonlinearity in single mode optical fiber by exposing a calculated length of fiber to the external electric field. The measurement technique is based on polarimetric detection and high accuracy is achieved in a hostile industrial environment.

High frequency (5 MHz–1 GHz) electromagnetic fields can be detected by induced nonlinear effects in fiber with a suitable structure. The fiber used is designed such that the Faraday and Kerr effects) cause considerable phase change in the presence of the external field. With appropriate sensor design, this type of fiber can be used to measure different electrical and magnetic quantities and different internal parameters of fiber material.

Electrical power can be measured in a fiber by using a structured bulk fiber ampere sensor coupled with proper signal processing in a polarimetric detection scheme. Experiments have been carried out in support of the technique.

Fiber-optic sensors are used in electrical switchgear to transmit light from an electrical arc flash to a digital protective relay to enable fast tripping of a breaker to reduce the energy in the arc blast.

Extrinsic sensors

Extrinsic fiber optic sensors use an optical fiber cable, normally a multimode one, to transmit modulated light from either a non-fiber optical sensor, or an electronic sensor connected to an optical transmitter. A major benefit of extrinsic sensors is their ability to reach places which are otherwise inaccessible. An example is the measurement of temperature inside aircraft jet engines by using a fiber to transmit radiation into a radiation pyrometer located outside the engine. Extrinsic sensors can also be used in the same way to measure the internal temperature of electrical transformers, where the extreme electromagnetic fields present make other measurement techniques impossible.

Extrinsic fiber optic sensors provide excellent protection of measurement signals against noise corruption. Unfortunately, many conventional sensors produce electrical output which must be converted into an optical signal for use with fiber. For example, in the case of a platinum resistance thermometer, the temperature changes are translated into resistance changes. The PRT must therefore have an electrical power supply. The modulated voltage level at the output of the PRT can then be injected into the optical fiber via the usual type of transmitter. This complicates the measurement process and means that low-voltage power cables must be routed to the transducer.

Extrinsic sensors are used to measure vibration, rotation, displacement, velocity, acceleration, torque, and twisting.

Type

Fiber optic amplifiers - Fiber optic cables

Autonics series

BF4R Series - BF3R Series - FT/GT Series - FD/GD Series

Photoelectric Sensors

A photoelectric sensor, or photoeye, is a device used to detect the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are used extensively in industrial manufacturing. There are three different functional types: opposed (a.k.a. through beam), retroreflective, and proximity-sensing (a.k.a. diffused).An opposed (through beam) arrangement consists of a receiver located within the line-of-sight of the transmitter. In this mode, an object is detected when the light beam is blocked from getting to the receiver from the transmitter.A retroreflective arrangement places the transmitter and receiver at the same location and uses a reflector to bounce the light beam back from the transmitter to the receiver. An object is sensed when the beam is interrupted and fails to reach the receiver.A proximity-sensing (diffused) arrangement is one in which the transmitted radiation must reflect off the object in order to reach the receiver. In this mode, an object is detected when the receiver sees the transmitted source rather than when it fails to see it.Some photoeyes have two different operational types, light operate and dark operate. Light operate photoeyes become operational when the receiver "receives" the transmitter signal. Dark operate photoeyes become operational when the receiver "does not receive" the transmitter signal.The detecting range of a photoelectric sensor is its "field of view", or the maximum distance the sensor can retrieve information from, minus the minimum distance. A minimum detectable object is the smallest object the sensor can detect. More accurate sensors can often have mimimum detectable objects of minuscule size.

Type
Photo micro sensors - Amplifier built-in type - Universal voltage type - U-shaped type -Cylindrical type

Autonics series
BJ3M Series - BS5 Series - BJ Series - BJN Series - BA2M-DDT BY Series- BYD Series - BPS Series - BM Series - BMS Series - BX Series - BEN Series - BUP Series - BR Series

Proximity sensor

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic or electrostatic field, or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor's target. Different proximity sensor targets demand different sensors. For example, a capacitive or photoelectric sensor might be suitable for a plastic target; an inductive proximity sensor requires a metal target.The maximum distance that this sensor can detect is defined "nominal range". Some sensors have adjustments of the nominal range or means to report a graduated detection distance.Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between sensor and the sensed object.A proximity sensor adjusted to a very short range is often used as a touch switch.

Type
Inductive square type Inductive cylindrical type Capacitive type Transmission coupler Junction box Accessories

Autonics Series
PFI Series AS Series PRCM Series PS/PSN Series PR Series PRA Series PRD Series PRW Series CR Series PET18-5 PT Series Connector cable (Socket-Plug / Plug-Plug type) Connetor cable (Socket / Plug type)

Company Profile

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Meyle (Germany)
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FSE Main Products.
Proximity sensors,Photoelectric sensors,Area sensors ,Fiber optic sensors,Door/Door Side sensors,Pressure sensors,Rotary encodersSensor, controllers,Switching power supply,
Temp. controllers, Temperature/Humidity transducers, Power controllers ,Recorders, Tachometer/Pulse(Rate) meters,Panel meters,Indicators,Signal convertors, Counters, Timers, Display units,Graphic panel, Stepping motors/drivers Motion controllers, ssr, Termocuples, Flometer, Ultra sonic sensor, Transmiter, Switch, Volt meter, Amper meter, Mark sensor, Tower lights, Selector swith, Clamp meter, Sound level meter, Infared temometer

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