omron FAQ

Frequently Asked Questions for Omron Photoelectric Sensors

Omron 3/6/2019

Question

To use the light of a Photoelectric Sensor through the hole, how large the hole should be?

Answer 

Please make the hole of the same size as the lens diameter basically.

Please refer to the following so that the idea is different depending on the sensing method.

1. Idea to use the light through the hole

Please make the hole of the same size as the lens diameter to secure corridors of light regardless of the through-beam or the reflective.

When holes are smaller than the lens diameters, the rated sensing distance might not be satisfied because the amount of light decreases.

2. Notes by the sensing methods are as follows

Omron Photoelectric Sensors FAQ

Question

Isn't there problem even if two light emitted from Photoelectric Sensor of different place intersects?

Answer

 There is no problem at all.

Omron Photoelectric Sensors FAQ

Question

What is "Wavelength of light "?

Answer 

Light is a kind of electromagnetic wave and has various wavelengths such as visible light, invisible ultraviolet light and infrared light

Description

Light is a kind of the same electromagnetic wave as the electric wave. It has various wavelengths such as visible light, invisible ultraviolet light and infrared light.

Light source used for photoelectric sensors is four types that they are blue, green, red and infrared.

Omron Photoelectric Sensors FAQ

Question

By what principle is the distance-setting Photoelectric Sensor detected?

Answer

 PSD and the dual photodiode are used for the light receiving element and the distance to the sensing object is judged by detecting the reflected light spot position on the light receiving element.

When the light receiving element is PSD The beam from the light emitting element (LED) is squeezed with the light emitting lens, and irradiated to the surface of the sensing object. And, a part of the diffuse reflected ray makes the spot on PSD through a light receiving lens.

The spot of light is made in "a" point when the sensing object is at the position of "A" that is the comparatively short distance and "b" point when it is at the position of "B" that is the long distance.

Omron Photoelectric Sensors FAQ

Therefore, if the spot position ("a" point and "b" point) on PSD is detected, the point turned on and the point turned off are set on PSD, and it can judge whether the sensing object is near or far compared with a setting distance. This is a principle of optical triangular measurement. 

It is the E3G-L to use this principle.

When the light receiving element is dual photodiode The beam from the light emitting element (LED) is squeezed with the light emitting lens, and irradiated to the surface of the sensing object. And, a part of the diffuse reflected ray makes the spot on the dual photodiode through a light receiving lens.

The position of the dual photodiode is adjusted so that N side and F side of the dual photodiode become the same amount of receiving light, and it is a setting distance. It is judged that the sensing object is nearer than a setting distance when the amount of receiving light is N>F, and judged that the sensing object is further than a setting distance when the amount of receiving light is N.

They are the E3Z-LS and the E3S-CL to use this principle.

Omron Photoelectric Sensors FAQ

No influence of the background object and the color or regardless of the amount of reflected light so that the distance-setting detects the receiving light position of the reflected light, and steady detection is possible.

Question

Is there a method of simply checking the trouble of a Photoelectric Sensor?

Answer

 If the tester is used, it is possible to check it simply.

It is checked in the following method whether the control output operates normally with a tester.

Omron Photoelectric Sensors FAQ

*This is simply operation check, and judges only the trouble of the control output.

Question

Can other models of Reflectors be used with Retroreflective Photoelectric Sensors instead of the supplied Reflectors?

Answer

 Yes, these Reflectors can be used: E39-R1, E39-R1S, E39-R2, E39-R3, E39-R9, E39-R10, E39-RS1, E39-RS2, and E39-RS3.

This does not apply, however, to Photoelectric Sensors for detecting transparent objects (E3Z-B, E3S-R, E3S-CR62/67, E32-R21, and E32-R16) or to the E3T.

Explanation: The following table gives the sensing distances for the Reflectors listed above.

Example: E3Z

Model Bare fiber diameter Flexing resistance data (light intensity retention, see note 3)
E32-T11
E32-D11
16 x 0.265 dia. Value after flexing 1,000 times at a bending radius of 4 mm (with no change)/Value after flexing 1,000,000 times (approx. 80%)
E32-T21
E32-T22B
E32-D21
E32-D21B
E32-D22B
4 x 0.25 dia. Value after flexing 1,000 times at a bending radius of 4 mm (with no change)/Value after flexing 1,000,000 times (approx. 85%)
E32-TC200
E32-DC200
1 x 1 dia. Value after flexing 1,000 times at a bending radius of 5 mm (approx. 95%)

Note:Tape Reflectors (E39-RS1, E39-RS2, and E39-RS3) can be used cut to the desired size.

Question

Our Photoelectric Sensors malfunction when the power supply of an inverter motor or other equipment is switched ON or OFF. What's causing this, and what can we do to resolve it?

Answer

 It's possible that the malfunction is due to electrical noise. Try a countermeasure for noise. Different countermeasures should be used depending on factors such as the path of noise entry, the frequency component, and the peak value. Typical countermeasures for various types of noise are shown in the following table.

Sensing method Features and other information
Reflective models (E32-DC200 and others) Used for detecting the presence of ordinary workpieces. Various Sensing Head shapes, sensing distances, etc., are available for specific applications. The operating range depends on the set direction (see note) of the Fiber Head.
Coaxial reflective models (E32-CC200, E32-D32, E32-D32L, E32-C31, E32-C41, E32-C42) Used for workpiece positional detection. The operating range depends on the set direction of the Fiber Head. (This is because a fiber for the Receiver is placed near the fiber for the Emitter.) Models other than the E32-CC200 and E32-D32L can be used as a small-spot reflective models when combined with a small-spot lens (E39-F3A, E39-F3A-5, E39-F3B, and E39-F3C).

Question

What are findings when a Photoelectric Sensor is selected?

Answer 

Please confirm below findings.

Omron Photoelectric Sensors FAQ

Question

How do the indicators on Photoelectric Sensors operate?

Answer

 There is a stability indicator (green) and an incident light indicator (red). There are four operation patterns depending on the amount of incident light.

Explanation: Stability Indicator The stability indicator shows the excess gain for temperature, voltage, dust, or other changes in the environment after installation.

Incident Light Indicator The incident light indicator shows the amount of light entering the receiver.

Omron Photoelectric Sensors FAQ

Indicator operation

Omron Photoelectric Sensors FAQ

Note:The operating level is 1.

The following figure shows indicator operation on a graph.

Omron Photoelectric Sensors FAQ

Question

What is a Photoelectric Sensor?

Answer

 A photoelectric sensor is the one to detect presence and the state of the object by the change in light.

1. What is a photoelectric sensor? Amount of light (luminance) is converted to an electrical signal, certain standard is set to a level of the electrical signal, the output is ON or OFF whether a level of an electrical signal (amount of light entered) is high or not than the standard.

2. Classification of photoelectric sensor

Omron Photoelectric Sensors FAQ

Question

What does the reversing polarity of power supply cause?

Answer

 Although it differs depending on the model, it doesn't operate at all (it is not destruction) or the operation mode is switched.

1. The sensor is not destroyed because the protection diode against reverse connection is certainly in it.

Omron Photoelectric Sensors FAQ

2. The diode bridge is in the power supply input, and the operation mode is switched. (*1)

Omron Photoelectric Sensors FAQ

(*1.)E3S-GS, E3S-VS, E3L, E3S-R[]E[]series

(Refer to the applicable date sheets for details.)

Question

What is the difference of NPN transistor output and PNP transistor output of the sensor?

Answer

Omron Photoelectric Sensors FAQ

(1) NPN output type is used when connecting a load between power supply + and sensor output terminal.

(2) PNP output type is used when connecting a load between sensor output terminal and power supply -.

This type is used a lot in Europe from the viewpoint on safety because the load is not driven even if somewhere of the wiring connected with the sensor output terminal is short-circuited with power supplies in some factors.

(3) The following is output circuit diagram of the E2E as typical.

Omron Photoelectric Sensors FAQ

Question

What is the repeat accuracy for Photoelectric Sensors?

Answer 

The accuracy depends on whether the Sensors are Through-beam or Reflective Sensors. The following table provides a general guide.

Omron Photoelectric Sensors FAQ

Note:

1.The values for accuracy are for reference only.

2.For Photoelectric Sensors, the repeat accuracy is the range of measurement error if the voltage, temperature, sensing distance, sensing object, and angle of the sensing object are the same.

Question

Is the serial connection possible in a Photoelectric Sensor?

Answer 

No, it is not.

Omron Photoelectric Sensors FAQ

When photoelectric sensor 1 is turned on, the voltage is supplied to photoelectric sensor 2 in above figure.

At this time, inrush current I2 when the power supply of photoelectric sensor 2 is turned on flows to the output of photoelectric sensor 1. (It is about 0.5 to 1A instantaneously in charging current of capacitor.)

The output short-cut protection circuit* of a photoelectric sensor works by this inrush current I2, and the output of photoelectric sensor 1 is turned off.

As a result, the voltage is not supplied between power supplies of photoelectric sensor 2 and cannot be operated. Therefore, the serial connection cannot be connected.

*Output short-cut protection circuit: It is the circuit that turns off output detecting the current and protects transistor, when overcurrent (above rated load current) flows to output.

Please use the serial connection by the combination with the sensor controller.

Question

What is the MSR (Mirror Surface Rejection) function of Retroreflective Photoelectric Sensors?

Answer

 MSR is a function of Retroreflective Photoelectric Sensors to receive only the light reflected from the Retroreflector by using the characteristics of the polarizing filter built into the Sensor and the characteristics of the Retroreflector.

Explanation:

1.Light that passes through the polarizing filter at the light emission side becomes horizontal.

2.Light will change from horizontal to vertical if it is reflected on the triangular pyramid on the Retroreflector.

3.The vertical reflected light passes through the polarizing filter at the light receiving side and reaches the light-receiving elements.

Omron Photoelectric Sensors FAQ

Using a Sensor with MSR is ideal for detecting mirrors or other mirror-like objects. By using the principles described above, a Sensor with MSR can detect a mirror-like object as shown in the following figure.

Omron Photoelectric Sensors FAQ

Note:If MSR is not used, the light reflected on the mirror-like object will be received, which will make it impossible to detect the object. The light will not be polarized at the object, and so the polarizing filter at the light-receiving side will prevent the reflected light from being received horizontally. This makes it possible to detect even mirror-like objects.

Question

With Retroreflective Photoelectric Sensors, is there any change in performance depending on whether the Reflector is placed vertically or horizontally?

Answer

 There is almost no change in ratings and performance.

Explanation:

The measurement values for Retroreflective Sensors in the catalog are for measurements with the Reflector placed vertically.

Omron Photoelectric Sensors FAQ

Question

Are Photoelectric Sensors that can be used in locations subject to water available?

Answer 

Using models that provide an IP67 degree of protection is recommended.

Explanation:

Items with an IP67 degree of protection satisfy the level of protection defined by IEC standard 60529 as shown in the following figures.

Omron Photoelectric Sensors FAQ

Typical models that provide IP67 protection are E3Z Series Photoelectric Sensors, E3S-A/B Series, and E32 Series.

For details, refer to Sensors Catalog. Be sure, however, to heed the following precautions.

1.Malfunction may occur if there is water on the lens surface. (Through-beam Sensors and Retroreflective Sensors may incorrectly detect light interruption. Diffuse-reflective Sensors may incorrectly detect light incidence, and the sensing distance will decrease.)

2.Photoelectric Sensors cannot be used if the case or lens is immersed in oil. E3S-C Series with IP67g protection (oil-resistant construction) is recommended for use in locations subject to oil.

Question

Are Photoelectric Sensors that can be used in water available?

Answer

 Yes. It is possible to use E32-series Optical Fiber Photoelectric Sensors, which have no electric components. Usage, however, is restricted by the model. Refer to the following conditions.

Explanation:

Only models with IP67 protection can be used. Side-view models, however, including E32-T24/D24 and E32-T14L/D14L, cannot be used even with IP67 protection because in the water, light will continue through without being reflected. E39-F1/F3 also cannot be used because the effectiveness of the lens will be lost.

Also heed the following precautions when using Photoelectric Sensors in water.

1.Light will be attenuated in water. The transmission rate will be as given in the following table depending on the type of light source.

Type of light source Transmission rate (%)
Installation distance: 1 cm Installation distance: 10 cm
Red light (650 to 700 nm) 98.5 86
Infrared light (940 nm) 80 10.7

Note:Use an Amplifier with red light that has a high transmission rate if the Photoelectric Sensors are used in water.

2.Depending on the light source, further attenuation may occur if residue or dirt becomes attached to the fiber surface.

Question

What is adjusted in the sensitivity setting of a Photoelectric Sensor?

Answer

 The amount of light emitted or the amount of light received are adjusted, and the sensing distance is set.

(The E3X auto tuning type is excluded.)

(1) Through-beam The amount of light received are adjusted, and the sensing distance is set.

(Refer to below figure)

(2) Reflective, fiber and others (Emitter and receiver are in the same case) The amount of light received or the amount of light emitted are adjusted, and the sensing distance is set.

* About the auto tuning amplifier, emitter current and the amount of light received are adjusted depending on a setting distance, and is set to the highest sensitivity.

Omron Photoelectric Sensors FAQ

Question

What are the methods of mutual interference prevention in through-beam photoelectric sensors?

Answer 

Point of mutual interference prevention The light of other sensor do not enter own receiver. Prevention methods are as follows.

1. Setting of out of parallel operating range

Please confirm parallel operating range on the catalog, install setting distance of adjacent sensor by 1.5 times min.

2. Alternate arrangement setting of photoelectric sensor

Up to two sets of emitters and receivers can be attached closely as following alternative arrangement.

Omron Photoelectric Sensors FAQ

Condition: The light of the next emitter might be received when the sensing object is close to the photoelectric sensor.

3. Use of mutual interference prevention filter

By use of mutual interference prevention filter, up to 2 sets can be attached closely. Mutual interference prevention filters are as follows.

E39-E6 for E3S-A  E39-E8 for E3S-B  E39-E11 for E3Z-T[][]A 4. Mutual interference prevention by adjusting sensitivity

When sensing distance is shorter than rating setting distance, the influence of mutual interference is nothing by lowering sensitivity volume though it depends on the customer applications and the selection models.

FAQ No. FAQ00428

Related Contents Primary Contents

Question

What happens when direct sunlight strikes to the lens of the receiver?

Answer 

Even if the light of a emitter is received, the sensor is the light shielding, or even if the light of a emitter is intercepted, the sensor is light entering, when direct sunlight enter the receiver. Therefore, please use the ambient illuminance by the sunlight 10,000 lx max as described to ratings/characteristics of the catalog.

Photoelectric sensors emit light by pulse and it turns on/off by level of the amount of light received.

The sunlight deletes the received light signal of the emitter and the sensor is the light shielding when direct sunlight strikes to receiver. Additionally, even if the light of an emitter is intercepted, direct sunlight is considered as receiving signal and the sensor is light entering. Therefore, please use the ambient illuminance by the sunlight 10,000 lx max.*

* The Value of the illuminance is approx. 10,000 lx max in shade. This value is changed the sunlight power. So, the value is just for your reference.

Question

By what principle is the limited reflective Photoelectric Sensor detected?

Answer

 In the optical system of the limited reflective sensor, only the regular reflection of a certain limited distance is received because the emitter axis intersects with a receiver axis in the same inclination θ.

Omron Photoelectric Sensors FAQ

In the optical system of the limited reflective sensor, the emitter axis intersects with a receiver axis in the same inclination θ as shown in figure. Only the regular reflection of a certain limited distance is received with such an optical system.

Therefore, only the object within the range where the emitter axis intersects with a receiver axis will be detected.

Omron Photoelectric Sensors FAQ

Moreover, the distance that reaches the peak of the excess gain never changes by the difference of the color because it uses the regular reflection. (However, the width of detection shortens by the amount of light reflection decrease.)

Question

Can a Photoelectric Sensor be used in outdoor?

Answer

 A photoelectric sensor doesn't warrant use in outdoor.

Influence of direct sunlight

The sunlight deletes the light signal of the sensor and the sensor is the light shielding, or even if the light of a photoelectric sensor is intercepted, direct sunlight is considered as receiving signal and the sensor is light entering, when direct sunlight strikes to the lens of the receiver.

Additionally, the temperature of the sensor becomes more than the operating ambient temperature by direct sunlight, and the sensor might be destroyed.

Deterioration of resin used caused due to ultraviolet light, rapid temperature change and icing

Material used for case deteriorate due to ultraviolet light included in direct sunlight, rapid temperature change and icing.

Malfunction by rain and fog

As for through-beam and retro-reflective, the light of the sensor diffuse by rain and fog, and might be dark-ON operation by attenuating the amount of receiving. 

As for diffuse-reflective, the light of the sensor reflects to rain and fog, and might be light-ON operation by receiving light.

Measures

Though it is not guaranteed when the sensor is unavoidably used, please avoid direct sunlight and wind and rain, and do not freeze by using a metallic type.

However, the malfunctions might be caused by rain and fog.

Question

How is the UL standard of the sensor of the DC power system treated?

Answer

 It is not necessary to use the UL standard certificated models in this case.

Please use the power supply certificated to the class 2 complying with the UL1310.

When you need to use the UL standard certificated sensors of the DC power system, Omron can provide the sensors that is certificated with the UL standards under the condition of "using in class 2 circuits".

Omron can provide the sensors with the UL standards certificated name-plate that is shown under the conditions of using in class 2 circuit.

Question

The Reflector is fogged up. Is there any way to improve the situation?

Answer

 Use E39-R1K Reflectors with a anti-fog coating. Regular Reflectors become fogged up when the temperature changes from -5°C to room temperature. Reflectors with anti-fog coating can withstand temperature changes from -25°C to room temperature.

Question

What is the allowable bending radius of coaxial cables or shielded cables for Photoelectric Sensors and Proximity Sensors?

Answer 

A minimum bending radius of five times cables diameter is recommended for coaxial cables and shielded cables.

Note:The minimum bending radius given above is the same for coaxial and shielded robot cables.

Reference Information:

For a standard cable, a minimum bending radius of three times cables diameter is recommended.

Question

What are the differences between E39-R1 Reflectors and E39-R1S Reflectors?

Answer

 E39-R1S has better reflection efficiency and directionality than E39-R1, so more light returns to the receiver, which enables a longer sensing distance.

For reference, the sensing distance for E3Z-R Photoelectric Sensors are 3 m with the E39-R1 and 4 m with the E39-R1S.

Question

We use Through-beam Photoelectric Sensors and malfunction occasionally occurs. What is the cause of this problem and how can it be corrected?

Answer

 The optical axis may have changed because of vibration or shock. If Sensors have a sensitivity adjuster, perform the following procedure to adjust the optical axis.

1.Set the sensitivity adjuster halfway between MIN and MAX.

2.Adjust the optical axes of the emitter and receiver at that sensitivity. Move the emitter up and down and to the left and right to adjust it to the center of the angle range for receiving light.  Move the receiver up and down and to the left and right to adjust it to the center of the angle range for receiving light.

3.Last, set the sensitivity adjuster to MAX.

Note:If Through-beam Sensors don’t have a sensitivity adjuster, use a slit to attenuate the light.

Question

Can a Slit and a Mutual Interference Protection Filter be used at the same time with E3S-AT Through-beam Sensors?

Answer

 No, they cannot. If they are used at the same time, the Slit will become tilted, and the sensing distance will be extremely short. Do not use them at the same time.

Question

Is it acceptable to wipe off dirt from the lens surface of Photoelectric Sensors with alcohol?

Answer 

No, it is not. The lens of the Photoelectric Sensors are basically plastic. Do not use organic solvents, such as thinners or alcohol, to wipe the surface. The lens surface may become clouded or cracked. Gently wipe away dirt with a dry cloth or use water.

The same applies to the Sensor case if the case is plastic.

Question

What role does the Slit play for Through-beam Photoelectric Sensors and how is it used?

Answer 

Role of Slit

The Slit is mounted on the emitter and receiver of Through-beam Photoelectric Sensors to decrease the lens diameter and narrow the light beam. This is done to increase the sensing performance for the smallest detectable object.

Usage

One set of two Slits for the emitter and receiver is generally used mounted to the emitter and receiver of a Through-beam Photoelectric Sensor. It is also possible, however, to use a Slit on only either the emitter or the receiver, depending on the sensing distance and the size of the sensing object.

Slits, however, cannot be used on Reflective Photoelectric Sensors (e.g., Retroreflective, Diffuse-reflective, Convergent-reflective, or Distance-settable Sensors).

Question

What are the differences between E39-R1 General-purpose Reflectors and E39-R1K Reflectors with anti-fog coating?

Answer

 E39-R1K Reflectors are the same as E39-RQ, except they have an anti-fog coating added to the reflective surface. The anti-fog effect of the coating is similar to that used by ski goggles.

The sensing distance with E39-R1K is the same as with E39-R1. For example, with E3Z-R Photoelectric Sensors with built-in amplifier, the sensing distance is 3 m whether E39-R1 or E39-R1K is used.

Question

We detect shiny objects using Retroreflective Sensors with the MSR (Mirror Surface Rejection) function, and malfunction occasionally occurs. What is the cause of this problem and how can it be corrected?

Answer

 Retroreflective Sensors normally have the MSR function, and so shiny sensing objects can also be detected. Perform a test before using Sensors for sensing objects with an extremely high degree of shine or for objects to which transparent film is applied, such as those objects in the following list. Reflected light received from the object may result in unstable operation.

Examples of Sensing Objects with Possible Unstable Sensors Operation

1.Cardboard boxes covered with a transparent sheet (i.e., shrink-wrapped)

2.Semi-transparent resin cartons

3.Aluminum vapor-deposited shiny vinyl bags

4.Cigarette packs covered with transparent vinyl

Using Through-beam Sensors are recommended for detecting sensing objects like those listed above.

Question

Are heat-resistant Photoelectric Sensors available?

Answer 

Yes, Fiber-type Photoelectric Sensors are available with heat resistance specifications. The heat resistance specifications, however, apply to Fiber Units only, and not to Amplifier Units.

Applications Detecting wafers in high-temperature environments

E32-T61-S Fiber Units

Omron Photoelectric Sensors FAQ

Ratings and Specifications

  150°C models 200°C and higher models
E32-T81R
E32-D81R
All other models
Min. bending radius 35 mm 10 mm 25 mm
Fiber material Plastic (fluororesin coating) Glass (fluororesin coating) Glass (SUS spiral coating)

Overview of Model Variations

Omron Photoelectric Sensors FAQ

Note:The sensing distances apply for use in combination with the E3X-DA-S Amplifier Unit (general-purpose, standard mode).