Written by: Roselius, Herb
These electronic devices, photoelectric sensors or photocells, use the light emission principle combined with the electronic and are made up of an emitter or luminous source, the light rays of which are detected by a receiver. The variation in luminous signal, obtained when interrupting this ray, is converted into an electrical signal and is measured and used by an electrical circuit. The light used is either infrared or red. By making use of this light various type of photoelectric sensors can be made.
The photoelectric sensors available in the FOTOSTAR range are the FT18M – FT18 – FTQ series in direct reflection, with reflector with polarized light and emitter-receiver versions. Due to their flexibility regarding the various standard programmable versions these products offer the possibility of stocking reduction an are easily interchangeable with most of the units available on the market. They are used in the field of automation to check for the presence, counting, position control, etc., and they are compatible with most logic programmers.
TYPE OF FUNCTION
DIRECT REFLECTION (P TYPE)
In this type of function the emitter of the infrared light and the receiver are close together. The sensing is obtained by the reflection of the rays from the object. In the use of these photocells it is important to bear in mind the color and the type of surface of the object. With opaque surfaces the sensing distance is affected by the color of the object, light colors correspond to the maximum distances and vice versa. In the case of shiny objects the effect of the surface is more important than the color. The sensing distance in the technical data is related to matt white paper.
REFLECTION WITH REFLECTOR (R TYPE)
This type also has the emitter and receiver close together.
The reflection of the light emitted is obtained by using one or more reflectors and the sensing the object occurs when these rays are interrupted. These photocells allow longer sensing distances as the rays emitted are almost totally reflected towards the receiver.
Similar to the R type, these photocells use an anti-reflex device, the use of such a device, which bases its functioning on a polarized band of light, offers considerable advantages and secure readings even when the object to be sensed has a very shiny surface. They are not in the technical data affected by random reflections.
THRU BEAM EMITTER-RECEIVER (B TYPE)
In this type of function the emitter and receiver of infra-red light face each other.
Sensing is achieved when this barrier of light is interrupted, they have a high reception as there is no dispersion between emitter and receiver. These photocells are therefore used for large distances where a high security of functioning is required.
Cylindrical construction M18x1 with housing and fixing nuts in stainless steel AISI 303. Types available in 10 ÷ 30Vdc NPN or PNP programmable and NO+NC static output, yellow led operation indicator and green led stability indicator, sensitivity adjustment incorporated. All types are available either with axial beam or 90° beam, cable exit or H plug for M12 connector.
Cylindrical construction M18x1 with housing and fixing nuts in plastic material. These are supplied in 10 ÷ 30Vdc with characteristics similar to the FT18M series and are also available with supply voltage of 20 250Vac with the possibility of programming NO or NC outputs. Types in direct current are only available with axial beam, cable exit without sensitivity adjustment.
Types in alternating current are also available with beam 90°, H plug exit for M12 connector and sensitivity adjustment.
Compact size in plastic housing, dimensions 50x50x18mm. Types available with supply voltage of 10 ÷ 30Vdc NPN or PNP programmable with NO+NC static output. Types available with supply voltage of 12 ÷ 240Vdc/ac (multivoltage) with relay output, programmable by means of a switch for the selection of the relay ON or OFF.
All versions are supplied with yellow led operation indicator and green led-stability indicator and trimmer for the sensitivity adjustment.
The FTQ series is available with cable exit or moving H plug for M12 connector to select the direction of the connector exit.
All the types in direct current with static output can be connected to normal or delayed power supplies of the ALNC-ALTP types and also to the CRTP rotation control.
- Our photoelectric sensors are immune to ambient light, attention should however be given to other light sources.
- In disturbed areas or areas that contain materials such as oil, powder etc., it is recommended that the barrier type separating emitter and receiver is used.
- In the use of photocells with standard reflector ensure that they are not too close together, abnormal functioning could result.
- Ensure the photocell is mechanically well fixed in order to avoid movement of the beam due to vibration.
- Attention should be given to the fixing of the connection wires keeping them separated from cables supplying motors, contactors, etc.
DESCRIPTION AND TECHNICAL TERMINOLOGY
SENSING DISTANCE (Sn)
It is the space in which it is possible to sense an object. In the case of direct reflection types it is the maximum distance between the photocell and the object, in the case of reflector or barrier types it is the distance between unit and the reflector or between units. (See drawing)
LIGHT ON / DARK ON TYPES OF OUTPUT
For the photocell the same terminology as inductive and capacitive sensors is used: N.O. = normally open, N.C. = normally closed. This refers to the state of the unit in the absence of product to be sensed. In the case of photocells light on / dark on is used. In the case of the direct reflection types N.O. is light on and N.C. is dark on. For the other types, N.O. is dark on and N.C. is light on.
TYPE OF LIGHT EMITTED
In photocells the light signal is directed via an optical system to the object to be sensed. All the light emitted by our photocells is solid state and can be red or infrared. It is easily modulated and has an unlimited life.
POWER ON DELAY
This is the time lapse between providing a power supply and the activation of the output and is to avoid unwanted switching when the unit is powered.
The maximum ON /OFF frequency that the photocell can carry out per second. The maximum values of every unit can be found in the technical characteristics.
NOMINAL VOLTAGE (Vn)
Indicates the maximum and minimum voltage values within which the photocell works correctly.
This is the relationship as a percentage between the alternating voltage (peak to peak) superimposed on the continuous supply voltage.
MAX OUTPUT CURRENT
This is the max output current of the photoelectric sensor in continuous function.
This is the max current consumption of the photocell referred to the maximum limit of the nominal voltage and without load.
VOLTAGE DROPThis is the voltage drop measured with the photocell with output activates.
SHORT CIRCUIT PROTECTION
All direct current photocells have an incorporated protection which protects the internal circuits from damage in the case of a short circuit on the output stage. Once the short circuit is eliminated the photocell resets.
INTERFERENCE FROM EXTERNAL LIGHT
The table shows the maximum limit of an incandescent light or sunlight. Beyond this limit the photocell may not work correctly due to interference on the receiver.
Temperature limits between which the correct functioning of the unit is guaranteed.
This is expressed in IP followed by two numbers. In the case of photocells the first always 6 (completely protected against dust) and the second can be 5 (protection against water spray) or 7 (protection against full immersion).
CONNECTION OF D.C. TYPES IN SERIES (AND LOGIC)
The photoelectric sensors connected in this way will activate one output when they are excited simultaneously. In this
CONNECTION OF D.C. TYPES IN PARALLEL (OR LOGIC)
Connected in this way all photoelectric sensors can activate the common output independently when excited. In D.C.
A.C. SUPPLY SERIES OR PARALLEL CONNECTION
In this type a short circuit on the output is not allowed. Incorrect connection can cause irreparable damage to the
SUGGESTION FOR SUPPLYING VOLTAGE TO PHOTOELECTRIC SENSORS
The supply voltage should be adjusted according to the characteristics of the sensor used. It is recommended to use
The secondary voltage Vac is found as follows:
The supply voltage Vdc of the sensor should be filtered with a capacity C at least 470 µF for each 200 mA used. If the