Photoelectric Sensors

Explanation of Terms

Application and Data

(1)Relationship of Lens Diameter and Sensitivity to the Smallest Detectable Object

With a Through-beam Sensor, the lens diameter determines the size of the smallest object that can be detected.

With a Through-beam Sensor, a small object can be more easily detected midway between the Emitter and the Receiver that it can be off center between the Emitter and Receiver.

As a rule of thumb, an object 30% to 80% of the lens diameter can be detected by varying the sensitivity level.

Check the Ratings and Specifications of the Sensor for details.

The size given for the smallest object that can be detected with a Reflective Photoelectric Sensor is the value for detection with no objects in the background and the sensitivity set to the maximum value.

(2) Detecting Height Differences

Selecting Sensors Based on Detectable Height Differences and Set Distances (Typical Examples)

(3) MSR (Mirror Surface Rejection) Function

Principles

This function and structure uses the characteristics of the Retroreflector and the polarizing filters built into the Retro-reflective Sensors to receive only the light reflected from the Retroreflector.

The waveform of the light transmitted through a polarizing filter in the Emitter changes to polarization in a horizontal orientation.

The orientation of the light reflected from the triangular pyramids of the Retroreflector changes from horizontal to vertical.

This reflected light passes through a polarizing filter in the Receiver to arrive at the Receiver.

Purpose

This method enables stable detection of objects with a mirror-like surface.
Light reflected from these types of objects cannot pass through the polarizing filter on the Receiver because the orientation of polarization is kept horizontal.

Examples

A sensing object with a rough, matte surface (example (2)) can be detected even without the MSR function. If the sensing object has a smooth, glossy surface on the other hand (example (3)), it cannot be detected with any kind of consistency without the MSR function.

Caution

Stable operation is often impossible when detecting objects with high gloss or objects covered with glossy film. If this occurs, install the Sensor so that it is at an angle off perpendicular to the sensing object.

Retro-reflective Sensors with MSR function

Note:When using a Sensor with the MSR function, be sure to use an OMRON Reflector

Retro-reflective Sensors without MSR Function

When detecting a glossy object using a Retro-reflective Sensor without the MSR function, mount the Sensor diagonally to the object so that reflection is not received directly from the front surface.

Selecting Transparent Object Sensors

Use the following procedure to select an appropriate Transparent Object Sensor.

(4) Surface Color and Light Source Reflectance

Surface Color Reflectance

Reflectance of Various Colors at Different Wavelengths of Light

Identifiable Color Marks

Applicable Sensor Light Colors: : Red light source : Green light source : Blue light source
Sensors with a RGB light source can detect all combinations.

These figures represent typical examples of ratios for light reflected by the back and mark.

Sensor light color	Product classification	Model
Red light source	Optical Fiber Sensors	E3X-DA-S
		E3X-NA
	Separate Amplifier Sensors	E3C-VS3R E3C-VM35R E3C-VS7R
Blue light source	Optical Fiber Sensors	E3X-DAB-S
Green light source	Optical Fiber Sensors	E3X-DAG-S
		E3X-NAG
	Separate Amplifier Sensors	E3C-VS1G
RGB light source (or white light)	Built-in Amplifier Sensors	E3MC-A
	Optical Fiber Sensors	E3MC-X/Y
		E3X-DAC-S

(5) Self-diagnosis Functions

The self-diagnosis function checks for margin with respect to environmental changes after installation, especially temperature, and informs the operator of the result through indicators and outputs. This function is an effective means of early detection of product failure, optical axis displacement, and accumulation of dirt on the lens over time.

Principles

These functions alert the operator when the Sensor changes from a stable state to an unstable state. The functions can be broadly classified into display functions and output functions.

Stability Indicator (green LED)
The amount of margin with respect to environmental changes (temperature, voltage, dust, etc.) after installation is monitored by the self-diagnosis function and indicated by an indicator. (Illuminates steadily when there are no problems.)

Operation Indicator (Orange LED)
Indicates the output status.

The margin is indicated by an indicator light, and the state is output to alert the operator.

Purpose

Self-diagnosis functions are effective in maintaining stable operation, alerting the operator to displacement of the optical axis, dirt on the lens (Sensor surface), the influence from the floor and background, external noise, and other potential failures of the Sensor.

Example: Light-ON Operation

Applicable Models

* Contact your OMRON representative regarding E3Z models with self-diagnosis output.

(6) External diagnosis input function (emission stop function)

Principle

The pink to blue wires in the Through-beam Emitter cable can be short-circuited to stop light emission at any timing. When there is no object between the Emitter and the Receiver, turning the light Emitter ON and OFF should cause the Receiver output to turn ON and OFF. Otherwise, there is a problem.

Purpose

This function allows the operator to check the operation of the Sensor before work begins.

Example: DARK ON Mode

Key Points

If the control output changes when the external diagnosis input is turned ON and OFF, the Sensor is normal. If the control output remains ON or remains OFF, the Sensor is faulty.

Note:When using the external diagnosis input function, it is assumed that the object does not interrupt the Sensor being checked from light.