Proximity Switches1

Inductive Proximity Switches (Series - SW 405)

Principle of Operation

Applications For Counting / Position Sensing of various objects in

Sensing Object Material

The standard Inductive Proximity Switches can sense any metallic (electrically conductive) object. However, we have special type of switches to sense either only ferrous objects or sense only non-ferrous (Cu, Al etc.) objects.

Sensing Zone

This switch has a dome shaped electro-magnetic field present in front of the sensing area. The switch will sense the object entering into this domain.

Sensing Distance (Sn)

This is the distance between the target and the sensing face at which the switch operates. This is usually specified considering M.S. as target material.

Correction Factor

Targets other than MS actuate the Inductive Switches at relatively less distance with correction factor as given below. However this criteria is not applicable to special "Nonferrous sensing models."

Correction Factor Table

Nonferrous Inductive Switches

All standard inductive switches sense presence of any metal but will offer stated sensing distance only for ferrous materials like MS.
The type SW 4051-NF is specially developed to sense only non-ferrous metals such as Copper, Aluminium, Gold, Tin, Zinc etc. The biggest advantage of this type of switch is that the non-ferrous objects are sensed from larger distances as compared to standard models. These switches are available in M18 and above sizes. The other operating features are same as those of standard 3 wire DC switches.

High Pressure Switches

Special high pressure type Inductive Proximity Switch has been developed for direct use in a Hydraulic cylinder.
The switch construction is sturdy and is rated for pressure upto 500 bar. These switches are also available in connector version for easy replacement.

Capacitive

Capacitive Proximity Switches (Series - SW 505)

Introduction

The series SW 505 Capacitive Proximity Switches are designed for sensing wide range of materials. These switches give a superior performance for detection of various non-metallic objects where Inductive type switches can not function.

The major applications of Capacitive Switches include sensing of

Working Principle

The switch works on the principle of resonant oscillator circuit. A pair of brass/copper disc from the electrodes of a capacitor & the object acts as a dielectric media. The change in capacitance value, due to presence of object, is sensed by a precision integrated circuit. An effective output signal is generated at a preset value of capacitance.

Construction

Sensing Distance

The nominal sensing distance of any size of switch is specified with Water as standard object and tested at 25°C. Depending upon the material of the object to be detected, the distance will vary. The sensitivity of the sensor is adjustable with a trimpot provided usually on the rear side of the sensor. Typical Sensing distance chart for a M30 size sensor, for different objects is shown in Fig.1

Effect of Ambient Conditions on Sensitivity

The sensing distance is affected by change in ambient temperature, humidity, size and material of the object.

General Specifications

Special Models

Special high Temperature models of Capacitive switches are available with Operating Temperature upto 150°C max. These switches are provided with a teflon front cap and with suitable teflon cable.
These switches are to be used with a specially designed controller/amplifier unit. The permitted operating length between sensor and the controller is maximum 5 meters. NAMUR type switches are available with CMRI-Certificate and approved Power Supply Unit with built-in Zener barrier circuit.

Protection

All the Capacitive switches are provided with Reverse polarity, Overload, short circuit and false pulse protections.
Rugged construction along with IP-67 grade of protection renders these switches to be very useful for liquid level monitoring applications.

Protection

Optical

Introduction

The Optical Proximity Switches are a reliable solution for automation where other Proximity Switches have limitations

These are Infra-red type sensors incorporating advance and reliable technology.

These switches have a distinct advantage of higher sensing distance over Inductive and Capacitive type of switches.

These can work more reliably in a noisy electromagnetic radiation environment. As an infra-red wavelength is used, it is immune to visible light interference.

Applications

These switches are very useful for counting and position sensing applications in Pharma, Food, paper, plastic & automobile industry. They also work effectively in level sensing applications for solids, grains, sand, ice and other non-metallic bulk material. Some typical applications are:

Principle of Operation

These switches incorporate an infra-red transmitter & receiver device housed in a single enclosure or separate enclosures. The precision pulsed transmitter beam is interrupted or reflected by the object. The advanced electronic circuit generates an effective output signal when the object is sensed.

Thru-Beam

(TB) type switches have separate transmitter & receiver. The object is sensed when the beam is interrupted.

Diffuse Scan

(DS) type switches have both transmitter & receiver in the same enclosure. The closely focussed beam is reflected back by the object.

Retro-Reflective

(RR) type switches use a special reflector to reflect back the beam. When an object interrupts the beam, an output signal is generated. These models have grater sensing distance compared to DS type. The receiver does not consider the reflection from the object.

Explanation of Technical Terms

The sensing distance specified for DS switch is considered with a white object having minimum 90% reflectivity.

This is the maximum specified range of a sensor measured at 25°C using a standard object.

These switches are offered in tabular metallic, acrylic & plastic enclosures. Standards models are available with integrated 2-meter long cable. Switches with built-in (Male) connectors (International M8 / M12 size) for quick connections are also available.

Special model of Optical Switches are available with an integrated Optical Fibre cable for flexible mounting and for sensing miniature objects / high temperature objects. This switch is of through-beam type and is available in H type enclosures.

Tubular / Rectangular / Slot type Enclosures

Magnetic

Magnetic Proximity Switches

The series SW 705 Magnetic Proximity Switches are available in two broad categories.

These switches are available in different shapes and sizes. Tubular models are available in Brass/SS enclosures in sizes M12, M18 and M30 and above.

SWITCHES WITH REED ELEMENT

These switches are used only for position sensing application. These incorporate a hermetically sealed sensitive reed element. The object should necessarily be a magnet. These are provided with 2-core built-in cable. The output is a potential free contact and can switch external load directly.

The switching voltage and contact rating depends upon switch size. Special models of latching type switches are available for direction sensing applications.

GENERAL SPECIFICATIONS

APPLICATIONS

Position sensing in hydraulic cylinders, Roto-meters, Direction sensing applications Level sensing of liquids

(Series MSP 706/MSP 716)

(Series MSP 707/MSP 717)

These sensors can be used only for sensing motion of a ferrous object e.g. Gear Wheel. These incorporate a special high strength ALNICO Magnet with a properly designed coil. Special high frequency sensors incorporate a Hall effect sensor.

These switches are available in 2/3-wire design. The 3-wire type switches have output logics / operating voltages similar to other types of switches described earlier. The 2-wire switches should be necessarily used with a special controller / amplifier unit.

APPLICATIONS

AUTOMOBILE SENSORS

Special / custom built models are available for Automobile applications as below

Ultrasonic

Ultrasonic Proximity Switches

(Series - SW 305 / SW 315)

The series SW 305 Ultrasonic Proximity Switches are ideally suitable for level monitoring applications. The Ultrasonic Sensors are available in different enclosures to detect various types of objects.

The sensing range covers from 0.2 m to 20 meters. The output signal is either in the form of a switching signal or a linear output current or voltage signal. These sensors have the ability to perform in dry and dusty environments. The performance of these sensors is not affected by the presence of impeding materials like Ash, Soot, and Sawdust etc.

These sensors are immune to electrical noise level generally present in the typical industrial environment.

WORKING PRINCIPLE

These switches incorporate a precise and delicate piezo Ceramic Ultrasonic transducer pair. The sensors are available in open as well as sealed type transducers.

The transmitter sends a modulated Ultrasonic Signal, which is reflected by the object.

A microprocessor-based circuit precisely measures the time taken to travel the distance from object to sensor. Effective output signal (either linearly varying or switching type) is generated depending upon application.

GENERAL SPECIFICATIONS

FEATURES

The Ultrasonic Sensors are provided with programming facility. General features available in programmable sensors are as below