HOW TO DETECT FROM AN OPTEL-TEXYS SENSOR? WITH OR WITHOUT ZEBRA TAPE?

The goal of this article is to highlight the possibilities of performing detections on rotating machines based on some variants of periodic elements.

The main concept to consider when assessing the feasibility of detection is contrast. It is based on the difference in the ability of two surfaces to absorb or reflect the light they receive.
It is generally agreed that a black surface and a white surface are contrasting from the point of view of the human eye. And the more strongly the black surface is able to absorb light and the white surface is able to reflect light very strongly, the greater the contrast is considered to be.
But this is not the only case where good contrast can be achieved. There are also the following solutions:
-    A "matt black" surface and a white reflective surface
-    A phonic wheel with teeth
-    The presence or absence of material, e.g. a slotted disc.
When using OPTEL-TEXYS sensors, the contrast must be considered with regard to near infrared light. As this is not in the visible range, care must be taken about the quality of the contrast on a part equipped with periodic elements and some preliminary tests must be carried out.
For optimal use of the sensors over a wide range of settings, it is necessary to have the highest contrast possible.

Before thinking about using the zebra tapes offered by OPTEL-TEXYS, it is always worth asking yourself the following questions:
-    Does my rotating machine have periodic elements?
o    If so, see if the contrast is sufficient
-    If not, can periodic markings be added directly to the part or can rotating elements with periodic markings be added?
o    If yes, the contrast obtained is generally sufficient
-    If not, consider using circular or linear test patterns.

To illustrate our point, we share below the different types of detection possible:
-    Periodic elements present by design on the target
-    Addition of a phonic wheel or slotted disc
-    Addition of OPTEL-TEXYS zebra tapes

Periodic elements present on the part

The presence of blades on the rotating part (turbine, turbocharger) is an opportunity to carry out the detection, whatever their material and colour:
-    1st example: black part in glass fibre; with or without marks on the blades

-    2nd case: turbine with shiny or matt surface; on blades, splitters or nut.

 
For applications on ball or roller bearings, the detection is carried out on these periodic elements according to 2 modes: either by light diffusion, i.e. emission and reception side by side; or in through-beam mode where emission and reception are separated (see the 2 photos below).

     

In order to scan a panel of representative cases, you will find below 2 configurations of detection on elements of an electric window lift motor and a gearbox pinion:
Connections from the winding

Rotor poles

Gearbox pinion
             
Advantages:
-    No additional embedded parts so no added mass or risk of unbalance
-    Very good contrast can be achieved
-    Need to fit optical probes into the available space; facilitated by small tip size and probe shape adaptation.

Adding a phonic wheel or slotted disc

External phonic wheels and optical encoders are used when periodic detection elements are not available on the machine.

They come in different forms:
-    Machined mechanical part with alternating teeth and recesses (A) that is installed alone or assembled in a housing (B)
-    Machined mechanical part with holes for radial detection (C)

(A)

(B)

(C)
       
On phonic wheel
             
On perforated disc
    

Advantages:
-    Adaptation of the number of tops per round
-    Obtaining a very good contrast
-    Insertion in confined spaces
Addition of OPTEL-TEXYS zebra tapes

OPTEL-TEXYS offers zebra tapes as accessories for users of its range of sensors and probes.
They have a very high contrast between the white and black marks and are well adapted to the detection wavelength used.
The tapes have scratch protection and micro-prisms on the surface. These offer the possibility of positioning the probe perpendicularly or at an angle to the target.
They are pre-glued for easy mounting and can withstand temperatures of up to 120°C over a long period.
Advantages:
-    Installation on a wide variety of parts as they come in circular and linear forms
-    Perfect contrast for OPTEL-TEXYS sensors
-    Provision of circular tapes from 15 to 360 stripes per revolution, also with missing tooth for acyclism analysis
-    Linear tapes for installation without disassembly on shafts up to 780 mm diameter.

The tapes catalogue is available on the OPTEL-TEXYS website: https://www.optel-texys.com/en/products/zebra-tapes-17/

Conclusion

We have presented a number of solutions for sensing rotating parts to measure angular parameters such as speed, position and acceleration.
This list is not exhaustive, but it suggests a number of possibilities for users of OPTEL-TEXYS optical fibre tachometers.
The main point to remember is that there are few limitations in detection solutions as long as you can achieve...
... a high CONTRAST between the reflecting and absorbing elements of the target.