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How to reach the minimum detectable object with a fiber amplifier?

Article No: KA-02132
Version: 2.0
Subject to change without notice
The article answers the question as to how one can reach the minimum detectable object with a fiber amplifier.
Related Products
LL3
LL3-TB01 LIGHT GUIDE (2 PCS/SET)
WLL80
WLL180
WLL190

Table of Contents

"Why does my fiber amplifier eg. WLL180T-P434 in combination with the fiber eg. LL3-TB01 does not detect the minimum detectable object (MDO) size of 0.5mm as written in the datasheet?"

 

One answer could be: If you look in a very bright light, you can't see a small object in front of the light source. If you dim the light you can see the small object in front of the light source.
Here possibly we have the same effect. Of course it could also be that the object is too fast for the adjusted response time. 

To answer this question in a more professional way, it helps to have a look on the performance triangle that we face in every similar application. 

 

As you know the three arrows have to be adjusted so that all of them respond exactly to the application's needs. If you improve one point the two others are getting more worse, meaning that everytime you change one arrow, both of the other two change as well. 
The challenge is to find the best fitting compromise.
You could have either:

  • slow response time = high sensing range  = bad detection of small objects because the receiver goes partly in saturation and will be insensitive or because the change of the currently received light value by the small object is too small compared to the very high value without object.
    or
  • fast response time = low sensing range = high sensitivity for detection of small objects.

The advantage is at the fiber amplifiers we have the screw available to adjust the response time to the application's needs. The disadvantage is you always have to find the best suited compromise in the application.

The worst case would be if we have a small detection object with the size of the MDO that moves very fast eg. in the free fall through the active area of the fiber and the customer needs the maximum sensing range. According to the performance triangle you know that's not possible. Therefore we have eg. to change the sensing range, find a different fiber eg. with a lens or smaller optic diameter ... 

To detect small objects with the size of the MDO, the sender light has to be reduced as much as possible by increasing the response time or/ and reducing the sender LED power. 
How to change the response time and other helpful explanations you'll find in the WLL180 technical information (unfortunately without part number):

setup of WLL80:
WLL80, 8027386 (sick.com)

page 12 response time:

another way to change the amount of light that the amplifier sends out is the power setting of the sender LED on page 25:

 
Keywords:
reach the minimum detectable object, datasheet, fiber amplifier, detection, light, performance triangle, response time, sensing range, minimum detectable object
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