Key indicator of sensing performance in weld cells

Posted by Steve Coulter on

Range-to-Diameter Ratio - something I have not seen yet on specifications, but possibly one of the most important considerations for selecting a sensor - and increasingly important as customers apply more sensors (and in more places).  Consider this comparison of 8mm sensors:

  • SENSOR "X" - 1.5mm range 
  • SENSOR "Z" - 3.0mm range

Assuming both sensors are high durable, with stainless steel sensing faces, tolerant to heat, WFI (weld field immune) and resistant to spatter.

The performance challenge with SENSOR X happens (1) when there are dimensional variations in the parts to be sensed and (2) when debris builds up on the fixture itself - this can be 1/2 to 3/4 mm, but perhaps even 1mm stacking the tolerances, leaving little safe operating zone of the sensor.  In this case, the mechanic may find it necessary to re-position the sensor very near (or on) the part, where contact, abrasion and heat will eventually take its toll, and replacement will be frequent.

With 3mm range of SENSOR Z, the 1mmm of stacked tolerances still leaves 2mm of unmolested sensing range (which exceeds that of the entire range of SENSOR X). It operates with the same parts and variations in parts placement repeatability, with adequate buffer of useable range that (1) requires just a single, one-time setup (2) does not need constant adjustment and (2) allows for greater distance from part reducing chance of contact and (3) allows for an air gap to reduce thermal gains.

So the equation for RANGE-TO-DIAMETER would look something like this:

 

  • 8mm dia. "SENSOR X"     (1.5mm Sn)     R:D=0.1875
  • 8mm dia. "SENSOR Z"    (3.0mm Sn)     R:D= 0.375

Now, to take another case with comparative 12mm sensors - most 12mm sensors in weld cells have between 2mm and 4mm of range (though some plants still use 1.5mm range sensors). So lets compare to a 3mm range 12mm vs. an available 6mm range sensor. Same performance assumptions: both sensors are high durable, with stainless steel sensing faces, tolerant to heat, WFI (weld field immune) and resistant to spatter. 

So the equation for RANGE-TO-DIAMETER would look something like this (R:D):

  • 12mm dia. "SENSOR X"     (3.0mm Sn)     R:D=0.25
  • 12mm dia. "SENSOR Z"    (6.0mm Sn)     R:D= 0.50

 Long sensing range has always been an important aspect of inductive sensors since early on ranges were very small (and damaged sensors were an accepted paradigm).  But significant technological advances have enabled inductive proximity sensors to achieve greater sensing range, triple and even quadruple range, while still maintaining an acceptable sensing pattern with flush mount capability in steel. In selecting sensors for use in weld cells, the RANGE-TO-DIAMETER ratio is another tool for engineers and maintenance technicians to consider, and can increase performance in welding environments.


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