EGE-Elektronik Spezial-Sensoren GmbH - Special-Sensors for Automation

opto sensors - Applications

System description
The Opto Edge controller consists of an amplifier (1) to which two  fibre-optic  cables  (2)  of  up  to  10  m  in  length  can  be connected via a rapid action coupling. The first fibre-optic cable routes a send signal generated by the amplifier to a first optical  converter  (3),  while  the  second  fibre-optic  cable returns a send signal detected by a second optical converter (4) to the amplifier as a receiving signal. This receiving signal is processed further in the amplifier into an output control  signal.
The Opto Edge controller works with infra-red light which issues extremely short and fast impulse sequences which enable  reliable  recording  of  rapidly  occurring  processes, even in the presence of influences from external rays. The process control system which is determined by the user, as well as the design of the optical converter, demands a high degree of flexibility from the system.

Band edge control EGE

Structure of the Opto Edge controller
In the system structure illustrated in Fig. 1 the optical converters (3, 4) are configured in opposing positions to form a photoelectric barrier. The material (5) which, for example, may be paper or a metal edge, pushes into the light ray and, depending on the depth of insertion, reduces the ray path of the light flow detected by the converter (4). The amplifier (1) which  is  connected  by  means  of  the  fibre-optic  cable  (2)  supplies a control signal (4...20 mA) to its output which is  proportional to the insertion depth of the material (5) depending on the formation of the optical converters (3,4) with a repeating accuracy of up to +/- 0.5 mm.

Sensitivity diagram

Opportunities for adjustment are provided on the amplifier (1) which ensure the exact adaptation of the fibre-optic cable types, optical converters or output signals, such as to discriminate digital switching or analog recording.
A particular advantage of the system is that the fibre-optic cable and the optical converter for transmitting and receiving are identical and, thereby, interchangeable. As a result, modification of the recording arrangement is reduced to purely construction measures. The photoelectric barrier process can be changed to a reflex process by a simple modification.

Detect band edge

In the reflex process illustrated in Fig. 3 the optical converters (3, 4) for the send and receive signals are arranged next to each other, e.g. above the material (5). With this arrangement the material does not interrupt the ray path between the sender and the receiver, but rather reflects a residual ray flow, which is detected by the receiver (4). The output corresponds to the distance of the materials. In this arrangement the result is also a current signal from the amplifier (1) which is propor- tional to the insertion depth of the material with high repeating accuracy.
In the case of the reflex process, however, accompanying conditions  which  are  included  in  the  measurement  result have to be taken into account. In particular these include the reflection factor of the material (5) or the reflection due to the background (6) which is not covered by the material. Influences of this type have to be taken into account during installation.

Recording of cracks, impact or non-homogeneity
Cracks or non-homogeneity in the area of the edges are principally recognised by the processes described in Fig. 1 or Fig. 3. In accordance with Fig. 1, cracks or non-homogeneity are recognized as short flashes of light while passing through, whereas in accordance with Fig. 3 depending on the background the reflection is briefly altered.

Recognition of cracks or irregularities in the material characteristics, e.g. also holes, is dependent on high speed reception on the part of the recording system. If, for example, in accordance with Fig. 1 a crack approx. 2 mm wide moves past the optical converter at a belt speed of 10 m/s the durati- on of the flash amounts to 0.0002 s. In this case, the optical amplifier has to have a resolution of at least 5 kHz. Similar conditions exist if, for example, border recognition with an accuracy of only a few millimeters has to be carried out for rapid pipe throughput in a section reduction rolling mill.

High capacity amplifier URA 408
This amplifier is intended for connection to a 24 V direct voltage power supply and has a 4....20 mA current output. The instantaneous current is displayed on a LCD display. The zero point (4 mA) and amplification can be adjusted independently enabling the characteristic curve to be shifted in parallel, as well as adjusting the slope. In order to span larger distances between photoelectric barriers or larger intervals between reflex scanning the send capacity can be switched to "long". These characteristics enable adaptation to a wide variety of opto-converters, fibre-optic cables or application requirements. The ultrared light generated by the amplifier has a high pulse rate of 50 kHz which enables reliable recording of rapid processes in the range of 8 - 10 kHz. In addition to this high input resolution the amplifier also has a high EMC tolerance which excludes the possibility of disruptive pulses being confused with event pulses.

Universal high capacity amplifier URA 5001
In  addition  to  the  basic  characteristics  which  have  been described for the URA 408 amplifier, this device has additional characteristics which make it universally deployable. It is also equipped for alternating current power supplies, has an additional 0...10 V Voltage output, as well as two PNP switch outputs. Upper and lower thresholds can be set for the entire characteristic curve range by means of a precision potentiometer. If the upper threshold is exceeded or the lower threshold not achieved the respective switch output closed and the corresponding LED is activated. If no threshold is affected the signal value is within specified limits. This is displayed by a third LED. This discrimination technology allows direct control or monitoring, e.g. that a belt is operating correctly, with preset permissible tolerances. For applications which require higher currents for switched mode operation or require a system control center which is without voltage the PNP outputs are switched to internally installed relays.

Amplifier OKZ 550
This amplifier is intended for use with the high performance trough beam sensors ULM. and ULL. A system consists of one transmitter, one receiver and one amplifier.

Fibre-optic cable Amplifier ULL
The amplifiers are used especially in high-temperature light barriers. Fibre optic cables are attached directly by means of rapid-action coupling. The fibre optic cables are used primarily in high-temperature zones, while the amplifiers are installed in zones with normal operating temperatures. The amplifier signal is connected to the analyser by means of a PVC or PUR cable that is up to 50 meters long.

Fibre-optic cable and optical converter
The fibre-optic cables used are made of glass fibre bundles which are installed in flexible stainless steel tubing or in a metal housing to protect them against environmental influences. They can be subjected to 250 °C and in special applications up to 350 °C. If a high degree of moisture is expected the stainless steel tubing is enclosed in an additional silicon sheath. The greatest advantage of the fibre-optic cable is that it is absolutely insensitive to electrical and magnetic influences, resistant to high temperatures, does not require a power supply and, for this reason, can also be used in areas where there is a danger of explosion.

Optical  cross  section  converters  convert  the  round  fibre bundle of the fibre-optic cable into a narrow high resolution light line which can either emit or receive optical signals. By means of this exclusively mechanical conversion a reaction sensitivity which has been achieved on one occasion is stable over time. For this reason electrical adjustment, such as that necessary for electro-optical systems, is not required. The optical cross section converters are supplied with a fixed pre-assembled fibre-optic cable and a rapid action coupling socket. This reduces losses along the optical transmission paths. Fibre-optic cables for connection to lens systems are equipped with rapid action coupling in both directions. It is possible to have fibre-optic cables up to 10 m long. The standard lengths are 2 m and 3 m. In order to achieve greater lengths fibre-optic cables can be connected by means of a coupler. The coupling loss consists of approx. 30 % and is permitted when there is sufficient light current.

Attachment Optics
Attachment optics focus the infrared radiation that is transmitted by the fibre optic cable. The have an angle of aperture in the range of 2...15°, which ensures precise object acquisition. They increase the range when used in light barriers. Attachment optics with a slit-type angle of aperture are best for acquiring objects on an inlet level.

For  high-temperature  applications,  fibre  optic  cables  and attachment optics designed for temperatures up to 250 °C (up to 350 °C upon request) are used.

Retro reflective sensor

Approval for safety applications
Sensors for personal security must have a qualifification approval according to EN 954-1 and must be labeled accordingly. Sensors that are not labeled must not be used for applications of this kind.

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