Pepperl+Fuchs Blog

Double Sheet Sensors… They’re Not Only for Paper

Posted by Zach Steck on Wed, Jul 02, 2014

Double sheet sensors originated in the printing industry to quickly and reliably detect the appearance of a double sheet or a splice in the paper.Ultrasonic sensors for double sheet detection

Due to this fact, double sheet is most commonly associated with paper targets.  BUT… this technology can also be used with a variety of other targets including plastics, metals, and even shiny or transparent materials.

In order to better understand this ultrasonic sensor, let’s first talk about it works.  The principle of double sheet detection is based on the reduction of ultrasonic signal strength by one or two materials.  We start off with two ultrasonic sensors positioned across from each other, one transmitter and one receiver.  The transmitter sends out an acoustic pulse that meets the boundary of the first sheet weakening the signal strength.  The sensor now knows that this is the single sheet condition.  In the case of a double sheet, the signal is weakened even further triggering an output.  These changes in amplitude allow the sensor to clearly distinguish the difference between no paper (air), a single sheet, and a double sheet.  This is represented in the drawing below:

Principles of double sheet detectionWith our PACTware software, we are able to view the change in amplitude detected when a double sheet condition occurs.  The first example - is using printer paper along with our UDC-18GM-400-3E2 double sheet sensor:

Double sheet detection - standard paperAs you can see, the process data displays three parameters: AMPLITUDE, RESULT, and SWITCHING THRESHOLD.  Let me explain these a little further:

  • AMPLITUDE is the raw value of the measured amplitude – without signal processing.
  • RESULT is the AMPLITUDE after internal signal processing/filtering.  This is used for the control of the outputs.
  • SWITCHING THRESHOLD corresponds to the set program and displays where the double sheet output will change state.

The UDC-18GM-400-3E2 features four different modes covering a wide variety of material thicknesses.  Upon selecting the appropriate mode, this sensor can be used to detect a double sheet condition with very thin metals and clear plastics.  Below, you can view the PACTware representation of these two materials:

Double sheet detection - Aluminum sheets

Double sheet detection - plastic

When the metals start to get a little thicker, we need a sensor with a stronger acoustic pulse such as the UDC-30GM-085-3E3.  This 30 mm diameter double sheet sensor is also equipped with four program modes covering a wide range of applications.  Let’s see what happens when we connect this sensor up to PACTware and detect a double sheet condition using steel sheets.  

You will notice that the varying thickness has an effect on the amplitude signal strength but is still reliably detected.

Double sheet detection - thin steel

Double sheet detection - thick steel

These examples represent only a very small percentage of the double sheet sensing capabilities found with these sensors. In almost every case, there is a sensor model or mode setting to handle the job.  Contact Pepperl+Fuchs today to find the right one for your next double sheet application!

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Topics: Ultrasonic Sensors

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