Best Practice for Photoelectric Sensor Installs
Sensing Range and Type Set-up
When setting up a photoelectric sensor for a new application, there are three major factors that must consider creating an easy installation with minimal adjustments: optimum detection distance, light source, and sensing width.
Four major types of models exist in order to overcome these factors.
Thru-scan Models
Separate emitter and receiver units are required for a thru-beam sensor. The units are aligned in a way that the greatest possible amount of pulsed light from the transmitter reaches the receiver. An object (target) placed in the path of the light beam blocks the light to the receiver, causing the receiver’s output to change state. When the target no longer blocks the light path the receiver’s output returns to its normal state. Thru-beam is suitable for the detection of opaque or reflective objects. It cannot be used to detect transparent objects. In addition, vibration can cause alignment problems. The high excess gain of thru-beam sensors makes them suitable for environments with airborne contaminants. Most thru-scan models come in three range types: short distance (for applications requiring sensitivity adjustment at distances of up to 1m), standard (for around 15m), and lone range (for long-distance applications or dust filled-filled environments such as automated warehouses, approx. 30m).
Diffuse-scan Models
The emitter and receiver are in one unit. Light from the emitter strikes the target and the reflected light is diffused from the surface at all angles. If the receiver receives enough reflected light the output will switch states. When no light is reflected back to the receiver the output returns to its original state. In diffuse scanning, the emitter is placed perpendicular to the target. The receiver will be at some angle in order to receive some of the scattered (diffuse) reflection. Most diffuse-scan models come in two range types: infrared (sensor has low susceptibilities to color difference to improve detection range for applications, approx 1m) and red (for near distance applications requiring visual confirmation of the directed spot, approx 0.5m).
Retroreflective Models
The emitter and receiver are in one unit. Light from the emitter is transmitted in a straight line to a reflector and returns to the receiver. A normal or a corner-cube reflector can be used. When a target blocks the light path the output of the sensor changes state. When the target no longer blocks the light path the sensor returns to its normal state. The maximum sensing range is 35 feet. Most retroreflective are standard types and offer some of the longest detection ranges available.
Wide Beam Diffuse-scan Models
These work similar to standard diffuse-scan models but cover a larger area of sensing capability. These models cover two types: wide beam long (for applications detecting print circuit boards and inclined objects, approx 100mm) or wide beam short (for sensing print circuit boards while minimizing interference from surrounding areas).
Common Problems in Installation
PROBLEM #1: Light axis is hard to adjust over long distances (thru-scan & retroreflective models) or noticeably inconsistent performance with black or non-reflective objects.
SOLUTION: Longe-range thru scan models have a light-operated indicator on the front and retroreflective models send out a visible red light beam for light access alignment over long distances. Diffuse-scan models offer the best long-distance detection standards in the industry along with consistent detection of darker colors.
PROBLEM #2: Interference between side-by-side sensors or the need to reverse the sensor configuration or move sensors.
SOLUTION: Thru-scan sensors using different frequencies can be installed side-by-side without mutual interference protection filter or reversed sensor orientation. Diffuse-scan and retroreflective models are fitted with automatic interference suppression that allows two units to be used side-by-side.
PROBLEM #3: Sensor operation is affected by inverter fluorescent light.
SOLUTION: New algorithms in new high-performance sensors achieve a major improvement in resistance to external optical interference. Look into high-performance sensors that are designed to work in multiple environments.
PROBLEM #4: Cutting oil mist near metalworking lines reduces sensor life.
SOLUTION: Sensors with polyacrylate resin lenses offer improved resistance to the effects of oils and chemicals.
PROBLEM #5: Plastic screw holes aren’t strong enough to support the sensor. Tightening the screws too hard or too quickly destroys the thread.
SOLUTION: Look for sensors that offer threaded metal mounting holes to provide improved mechanical strength.
PROBLEM #6: Sensor doesn’t operate in freezers at -30° C or can’t perform well in sunlight.
SOLUTION: Don’t believe what other companies tell you; there are sensors that exist that perform in these frigid and well-lit environments. If a company doesn’t make a sensor able to operate in these conditions, it is time to move on.
Choosing the Right Sensor
When choosing the right sensor, you’ve got to pick one that fits the particularities of your work environment, not one that makes you change the environment of which it operates.
To obtain optimal accuracy and high performance, choose a photoelectric sensor that is built durable and progressive enough to last.
For more information on what All World can offer in photoelectric sensor capabilities take a look at our highly recommended Azbil / Yamatake HP7 series sensor, which promises to provide a solution to all of the common problems listed in this blog.
