Do Photoelectric Sensors Really Measure Up?

I recently spent the week at the IMTS show in Chicago. If you have never been to this show I highly recommend you go in 2012. The show occupied over 1.1 million square feet and there were over 1700 manufacturers and or vendors. If you do attend this show I think, you really need take at least two days to go through it. No matter how comfortable you think your shoes are I guarantee that your feet will hurt after going through the four buildings of exhibits.

While I was working at our booth, I had several customers ask me about using photoelectric sensors in measuring applications. The questions ranged from the basic how they work, what are some of the application concerns to the infamous what is the accuracy of the sensor.

Here are some of the highlights to summarize our conversations:

• There are two types of technology utilized in photoelectric sensors that are used in measuring applications. First is triangulation the sensor basically measures the angle of the reflected light from the target. This methodology is used in short-range sensor with higher resolutions. For more information, check out our previous post on BGS sensors.

• Time of flight is the other technology used. With this method, the sensor sends out a pulse of light and the sensor calculates the distance by timing how long it takes for the light to return to the sensor’s receiver. This technology is used for medium to long-range distance measuring photoelectric sensors with lower resolution.

• Make sure the spot size is correct. If you are trying to measure a porous surface like a grinding wheel, the light spot needs to cover the edges and not the deepest point. Keep in mind that the spot size will change depending on the distance the sensor is from the target. Also infrared light source is believe it not or not more powerful than laser in dirty environments.

• Try to keep the object in the center of the sensors range. Don’t forget that typically there is a blind spot in the first few millimeters of the sensor’s lens.

• Accuracy…whatever! Let’s stick with resolution, which by definition (check out our previous entry on resolution) the smallest increment of position changes that can be detected and indicated by the output. There are several factors that will affect accuracy including temperature, humidity, dirt on the lens, contaminants in the air, range, age of the emitter and the list goes on.

As one gentleman said when he asked how they worked and what considerations needed to be taken into account “there is more to them than I thought”. However, if properly applied photoelectric sensors can provide very precise measurements or be used for small object detection or verification.