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Tips for Mounting Inductive Proximity Switches

Why inductive?

Inductive proximity switches are highly popular with end-users. They are

  • robust
  • good value for money
  • insensitive to dirt
  • standardized

and, as a result, simple to employ.

Type of Mounting Embeddable / Nonembeddable

Surrounding Metal Parts

Not only metal parts in the plane of the sensing face, but also those alongside or in front, influence the field and consequently the response of the device. As far as the type of metal is concerned, the information given in section 1 is also valid in this case. As a result of the vast number of mounting possibilities, useful information from the manufacturer is limited. When the spaces referred to in Figs.1 to 6 as "metalfree zones" can really be kept free of metal, then problem-free operation can be assumed. In principle, in this case, the following is also valid: as a result of embedding conditions, the operating distance should not vary by more than 10% relative to its value in free surroundings. If there is any doubt, this must be checked by means of a measurement.

Operating Distance Adjustment

Mutual Influence with Aligned Devices

Mutual Influence with Aligned Devices

The mounting of several proximity switches with limited spacing (Fig. 10) can, as a result of inductive coupling between the oscillator coils, lead to mutual influence and as a result, to signal fallout.

This case deserves particularly careful clarification, since the disturbances are not always immediately conspicuous, but may only occur sporadically.

For such installations, the corresponding information from the manufacturer concerning the minimum spacing to be observed should first be consulted, and whenever possible adhered to. If in a specific case it cannot be adhered to, there are various possibilities:

  • Install embeddable devices, since the required spacing compared to the housing diameter is significantly smaller;
  • Use smaller proximity switches; the required spacing is disproportionately smaller;
  • As far as the application permits, switch the supply voltage to the device on and off in such a way that neighboring units are never under tension at the same time. For instance, with processes that are not too fast, a kind of multiplex operation that removes disturbances in an elegant manner can be arranged;
  • Use devices with different oscillator frequencies. These are available from most manufacturers as special versions. Two frequencies are often enough, provided the devices with these frequencies are installed alternately. This solution is however problematic for several reasons:
    • special devices, which are more expensive and not stock items, are required;
    • the risk of mix-ups during mounting is considerable;
    • the logistical cost (spare parts stock, additional article, stock lists) increases;
    • problems during the field replacement of spare parts can hardly be avoided.
  • Use devices with the same dimensions, but from different suppliers. In this case, the oscillating frequencies are generally different, but this must first be clarified. Since oscillator frequencies are not given in catalogs, they must be requested from the manufacturer. The frequency difference should be at least 10%. For mounting, the information given further above is valid.

It is strongly advised to avoid any action just on the off chance that it may work. The oscillator frequency scatter between devices of the same type and the same manufacturer can often be enough to achieve a seemingly good result without further measures. Though whether next time it still works is a question of pure luck, to say nothing of mounting spare parts in the field.

Fixing

Threaded Cylindrical Devices

Threaded Cylindrical Devices

In compliance with the manufacturer’s instructions, the maximum tightening torque of the nuts must be respected; the housing is hollow inside and therefore supports less load than a screw with the same diameter (Fig. 11). This is particularly important for small sizes. Moreover, it must be borne in mind that the wall thickness of the housing can be thinner for a few millimeters at each end, and that therefore the given tightening torque may perhaps not be attainable at these points. Where vibrations are present, the use of an additional safety-locking washer is recommended.

Smooth Cylindrical Devices

Square Devices

Smooth-walled devices are best fixed by means of clamps (Fig. 12). Cementing may also be possible. The use of adjusting screws should be avoided; they lead to deformation of the housing, and can lead to total device failure.

Square Devices

It must be ensured that the mounting surface is sufficiently smooth, so that when tightening the fixing screws, the device is deformed to a negligible extent only. In this case also, where vibrations are present, the use of an additional safety-locking washer is recommended.

Connector / Cable Assemblies

LED

If possible, the LED should be visible after mounting, for which the commissioning and maintenance personnel will be thankful. It is often sufficient to turn the device in the right direction. For devices with cable connections, a rearwards oriented LED is advantageous for visibility; on the other hand, this is often a disadvantage for the quality and durability of the seal between the housing and cable. For devices with socket connections, the use of a connecting lead with a built-in LED can guarantee a better visibility.

Labeling

In the case of spare part mounting, the importance of the device label should not be underestimated. For this reason, it is not of primary importance to place a high value on an aesthetically satisfactory label, but rather more on a permanent one. This is especially valid in a mounting situation where the device is in permanent contact with liquids. Less recommendable is the application of the label on the sensing face. As is well known, despite all precautions, abrasion (which in addition also endangers the life of the device) must be reckoned with. It must be borne in mind that, in case of failure, the label may no longer be readable.

The manufacturer’s original labeling is nearly always carefully optimized, and therefore of good quality. The problem frequently only arises when the user applies company-specific additional labeling, e.g. part numbers. The additional cost required to provide first-class durability is easily dispensed with and, as a result, problems when replacement parts need installing are involuntarily provided.

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