Pepperl & Fuchs Valve Position detection
The success of the inductive proximity switch has flourished throughout the history of automation. The advantages of this type of sensor includes its non-contact, wear-free principle, compact design, availability in countless versions and its exceptional robustness and insensitivity to the typical environmental conditions in industrial plants, such as dust, dirt and humidity. Its field of application is extremely broad and ranges from the detection of a Valve Position, detection and the positioning of individual work pieces or machine elements, welding or conveying facilities, through to rapid counting tasks.
Necessity as mother of invention
In 1958 - the proximity switch was invented in a Mannheim laboratory owned by Pepperl+Fuchs. What was originally conceived as a customer-specific solution for an intrinsically safe current circuit in the chemical industry, has since become the universally recognized industry standard for non-contact switching. Thus the proximity switch is one of the oldest and most successful electronic components in automation, due to the fact that it has been continuously reinvented over the years to keep pace with ever-changing requirements.
The inductive proximity switch was invented in 1958 by Pepperl+Fuchs in Mannheim. Walter Pepperl and his colleague Wilfried Gehl were commissioned by BASF to find an alternative to mechanical contacts in intrinsically safe current circuits. On the one hand, the conventional switching devices used by the company had to withstand the corrosive atmosphere of a chemical plant. On the other, the energy required for self-cleaning through contact erosion was not available due to current/voltage limitations for explosion protection reasons. Nowadays the inductive sensor replaces the mechanical switch because of various reasons.
Inductive sensors versus Mechanical switches
Long service life through absence of wear
Before we put the properties and advantages of Pepperl+Fuchs Valve Position sensors in the spotlight, first the following remarks:
It must be taken into consideration that aside from the hard to prove advantages of the Inductive valve position sensors compared to mechanical switches, we need to take away some prejudices in people that have been using mechanical switches or reed contacts for many years.
Change in working methods or technology, very often creates resistance in people that are responsible for the implementation of the new product (we have done it like this for many years without any problem, so why would we change?). At the same time, people can hear or feel the mechanical switch clicking from one position to the other.
The next summary gives you a good idea why it makes sense to use inductive sensors:
One thinks that only a mechanical switch can easily be tested by an Ohm meter.
On the market, you can find simple testers for every inductive sensor (see fig.1)
Insensitive to humidity or dirt (IP 67)
Water intrusion or presence of condensation in the switchbox, is a well known phenomena in the process industry. This humidity which cannot escape thanks to the high quality seals of the box, will affect the reliability of the mechanical switch in the long term. This can easily be avoided by making use of an IP67 protected Inductive sensor which is available in different shapes and electrical versions (Fig2: NCB2-V3-N0.
No moving parts, therefore maintenance free
High electronic precision and reliability.
Simple and reliable lead breakage and short circuit monitoring (Namur sensors).
Valve Position Sensors Direct Mount concept
For standard applications, more and more direct mount valve position sensors are used. They minimize space requirements; maintain assured sensing distance, and offer simplicity and sophistication in monitoring and reliability. Summary of advantages of the Pepperl+Fuchs Valve Position sensors:
No protection needed for outdoor use.
Clear LED indication for switching status for Valve positions, status solenoid and power
Quick and simple installation, no adjustment necessary.
Only 2 pucks (targets) needed for all sizes of actuators.
Pucks are suitable for quarter turn, left and right turning actuators, and for 180° actuators
Electrical connection either via cable, connector or terminal compartment.
Available for Ex and non Ex versions
Electrical versions in 3-wire DC, Namur (Exi) and AS-interface. Also available in 2-wire DC or AC/DC to be compatible with existing installations.
Possibility to wire the solenoid via the sensor.
Pepperl + Fuchs Ltd, Tel: 0161 633 6431
Published in Valve User Magazine Issue 15
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