How to Calibrate a Label Sensor

Whenever your labeler is dispensing labels, the output LED on the label sensor should light up exactly one time per label. Generally, this is a quick flash as the gap between the labels passes through the sensor, but the LED can also be on for the length of the label and go out when the gap passes through. For these instructions, we will send an output signal when the gap is at the sensor.

To test your label sensor setting, simply power on your labeler and hold a length of labels in the normal path through the sensor. It is vital that you duplicate the exact location and tension that goes through the sensor during operation, so if you can hold the web of labels around the upstream roller and downstream roller or peel edge, that is best. Move the labels back and forth through the sensor. You want the LED to come on at the gap and never anywhere throughout the label.

The exact buttons you push to calibrate the label sensor are different on every machine, but generally you press and hold one button on the sensor for 2-3 seconds to put it into teach mode. Then, keeping tension on the web, place a gap in the sensor path (usually a red light will project onto the gap between labels) and press and release the same button. The LED will probably flash. Finally, place the label under the sensor and press the button again. The LED will flash again, and the sensor will automatically switch back into run mode.

Some sensors have two separate buttons labeled on and off. “On” goes with the gap, and “off” goes with the label. It really helps to have either the labeler manufacturer’s instructions or the sensor instructions to figure out the exact button pushing sequence. Also, the LEDs will flash in different patterns to tell you different things. Try to find the sensor instructions. Most of them are available on the Internet.

Some older machines have a dial you turn to adjust the label sensor. On these, position the gap at the sensor, turn the dial down until the indicator light goes out, then slowly turn it back up just until the light comes back on. Write down this setting. Now put the lightest part of your label at the sensor. The light will have gone back out. Turn up the dial until the light comes on again, and write down that setting. Now turn the dial to a number halfway between the two you’ve written down, and you should be there. Pass the label back and forth past the sensor to verify that the light comes on only at the gap. If it comes on at any point inside the label, turn the dial down a little. If the light does not always come on at the gap, then turn the dial up a little.

*Important* When you place the label in the sensor, you should put the lightest part of the label at the sensing point when you press the button. Hold a label up to a light. If you can see more light coming through one area of the label, then calibrate the sensor at that spot in the label. This is because the sensor will take a reading of the amount of light that passes through the liner (at the gap) and through the liner plus the label (at the label) and select a point approximately halfway between to switch its output between on and off. If you calibrate to an especially opaque portion of label—perhaps at some black or metallic ink—and the sensor averages that with the liner, it may end up at a switching value near what it sees at a less opaque area of label where there is no printing on it. This will cause a false trigger and your label will stop short.

Another way to prevent false triggers throughout the length of the label is to position the edge of the label halfway over the sensor for that part of the calibration. The sensor will see more light than when it is fully covered and will set the switch point closer to that of the liner by itself.

There will always be an unusual situation that requires another trick—or sometimes a different type of label sensor altogether. If the above instructions don’t work for you, call me at 800-331-7140 or email me at jdawson@su-solutions.com, and we’ll figure it out together.