Magnetic Switches


Working Principle Magnetic Switches/Reedsensors
Magnetic switches work contactless either on a reed contact basis or as a fully electronic sensor, actuated by a magnet. At reed contact the paddles (reed ends) are magnetised and close or open when approaching the magnetic field when there is sufficient magnetic force flow. Due to various sensitivities of the reed contact and the field strength of the magnet, different sensing distances are possible. Fully electronic magnetic switches measure the change of the magnetic field and convert it into a digital signal.
Structure of a reed contact
The reeds are hermetically melted into a glass body filled with inert gas. The reed ends coated with rhodium overlap with a short distance (air gap). When approaching a sufficiently strong magnetic field, the reeds move toward one another and thereby close the contact.
Structure of a fully electrical magnetic switch
The Hall/magnetoresistive  sensor elements actuated by magnetic fields detect the field strength changes and provide an analogue or digital signal.
As these magnetic switches without mechanical contacts they are wear-free. These switches include a power output stage and are reverse polarity and short-circuit protected.
Switching Functions
Reedcontact Switches
The contact studs are magnetized and make, on reaching the specified AW number, with a characteristic snap action as soon as a magnet approaches. The polarity of the switching magnet do not have to be taken into account for the make contact because both the magnetic north and south switch in the same manner.

Normally open

In the off-position, the contact studs are based by a leader magnet. At the approach of the switching magnet, the magnetic field of the leader is neutralized and the biased contacts stud break.

Normally closed

The change-over (make-break) contact consists of one movable and two fixed contact studs. In the off-position, the movable contact studs are retained by spring action so as to rest on the fixed studs (break contacts). At the approach of a magnet, the movable contact stud is attracted by the make contact. The break contact opens and the make contact closes with a jerk. The polarity of the switching magnet does not need to be taken into account because both magnetic north and south switch in the same manner.

Change-over contact

With the side stable contact, a leader mag-net (whose field intensity is rated such that the contact studs are retained in the postition determined by the approach of the switching magnet) is allocated to a special contact. The opposite switching function is achieved by changing the magnet poles.

Bistable (catch switch)

Exposure to iron and power cables layed parallel to the device may influence magne-tic switches. The minimum clearance bet-ween the reed-magnetic switch and a power cable should be 50 milimetres. Also, when installing magnetic switches in series, there should be an adequate space between the individual devices as, depen-ding on the capacity of the relevant swit-ching magnets, an undesirable triggering of the next-in line switch may otherwise oc-cur. Interferences of this nature may, how-ever, be eliminated by applying screening shields. On the other hand, by absorbing a part of the magnetic field lines, the maximum switching distance is, in the case, reduced. SECATEC- Magnetic Switches are partly furnished with screening shields as standard equipment (our elevator switches series MKF24A…).. Please do not hesitate to contact the company with further questions.
On-transition Time
Depending on the reed contact size, the cut-in delay will be 0.6 to 4 ms.
Release Time
Depending on the reed contact size, the re-lease time will be 0.07 ... 0.5 ms.
Bouncing Time
Bouncing time with small contacts is 0.3 ms and 0.5 ms with large contacts.
Switching Distance
The switching distance is the distance be-tween the operating magnet and the magnetic switch. It is determined by the sensitivity of the reed contact (AW value) and the operating magnet's field intensity. The biggest magnetic switch-to-permanent (disc type) magnet switching distance will achieved by mounting the magnet directly onto iron using a non-ferrous screw. The iron base serves to concentrate the magnetic field and to achieve a wider range. If, on the other hand, iron screws are used for fixing the magnets, then part of the magnetic field is short-circuited inside the bore hole and the range is thereby reduced. The magnetic switch can be triggered, at option, either in front or at the mark on the side.
Switching Hysteresis
The operating magnet's cycle between the ON/OFF switch points reflects the switching hysteresis. Moreover, it may be influenced by a ferriferous environment. The hysteresis will always depend on the reed contact or on the magnetic sensor element and the operating magnet.
Switch Point Precision
The reproducible switch point precision of magnetic switches under constant conditions is extremly high  in the range of 0.01 mms. When using barium ferrite (disc type) ma-gnets will be shifted with change in the ambient temperature, the magnetic field being stronger with lower temperatures and weaker with an increase in temperature. The reaction to temperature is not linear, with the magnetic field hardly increasing at temperatures below 0 deg. C and a negligible decrease only when the temperature exceeds 100 deg. C.
Vibration resistance
To protect the glass ampoule and the other components and to increase the vibration resistance, the reed contacts are cast in high-quality casting compounds. Sensitivity to vibrations and oscillations is at its lowest in the axial direction. Given an elastic fastening, magnetic switches of a monostable design may be subjected to vibrations of up to 100 g.
This value is practically never reached in operation. However, it is exceeded when the switches fall from a high position onto a hard surface. Shocks to the housing and deformations due to overtightening of the mounting screws must be avoided.
Magnetic switches of a bistable design with an elastic fastening are suitable for vibrations of 10 to 20 g (g beeing the accelleration due to gravity, i.e. 9.8 m/s²).
Service Life
Service life (without electric load) covers 109 switch actions and even up to 108 switchings can be reached if the electric limiting values are adhered to and adequate spark extinction is provided for. Full electronical magnetic switches work without mechanical contacts and therefore show no signs of wear. They virtually have an infinite service life.
Contact Rating
The magnetic switch working range is shown on the contact rating hyperbola below: Neither the maximum voltage, nor the maximum current or maximum capacity indicated in the catalogue may be exceeded.
Contact Protection
The service life of a magnetic switch de-pends to a considerable extent on the load conditions. Considering that the maximum contact ratings refer to purely resistive loads that are not always warranted in practical applications, adequate measures for protecting the contacts are required with diverging loads.
Inductive Load
In the case of D.C. voltage, a free-running diode is to be wired up parallel to the load. The polarity has to be such that the diode will inhibit under service voltage feed and will short-circuit the inverse peak voltage occurring when the contact makes.
When wiring up a A.C. voltage, an RC mo-dule has to be connected parallel to the contact (i. e. in series to be load) for attenuating arcing. RC module size (by rule of thumb):
R in Ω ~ R in Ω of load
C in μF ~ I in Amps
Capacitative Load
The increased inrush currents at capacitive loads can largely be reduced by a series resistor to the capacitor. In this area longer control cables are also required, because the parallellying wires act as a capacitor. From a cable length of 20 m the occurring capacitive loads can be critical.
Switching of lamp loads (light bulbs)
When incandescent light bulbs are switched on, a much higher current than their rated value briefly flows through them. This switch-on peak current can be reduced by a resistor connected in series. Also, by connecting a resistor in parallel to the switch of the filament, it can be preheated to such an extent that it comes as close as possible to the glowing status.
Standard magnetic switches are suitable for application at temperatures of -25 to +80 deg. C, and temperature-resistent switches at temperatures of -40 to +200 deg. C.
Please note:
Errors/printing mistakes excepted. We reserve the right to change the technical details without notice. Only the customer knows all the conditions / influencing factors. He is therefore in principle required to qualify our equipment for his proposed application itself. A legally binding assurance of certain properties or suitability for a specific application can not be derived from our datas. Applications are inadmissible when safety of persons depends on the function of our switches/sensors.

Inductive Switches


Principle of Operation (inductive)
Inductive proximity sensors provide an ex-cellent means for detecting the presence of a wide range of metallic targets. This detec-tion is accomplished without contacting the target and is mechanically wear-free. In principle, an inductive prox. switch is com-prised of a high frequency oscillator circuit followed by a level detector and a post amplication signal circuit that drives a buffered solid state output. In effect, when a metallic object is brought within the effective range of the omitted field of the oscillator, a damping action results which reduces the amplitude of the oscillator. The amplitude shift is converted to a digital signal by the level detector (ie: a Schmitt trigger) which drives a buffer stage. When the object is removed, the oscillator and the digital output is returned to its former state.
Definitions according to
EN60947-5-2 (DIN VDE 0660)
Mounting in Metal
Shielded Construction

Shielded prox. switches can be mounted in a metallic material with no loss in sensor performance as long as the active surface of the sensor either protudes, or in the worst case, is mounted flush with the metal surface. For standard models, each sensor must have at least one Ø of clearance between it and other sensing surfaces.

Unshielded Construction
Prox. switch models of this type require a metal-free zone of three times its own Ø around its active sensing surfaces. The only other alternative is to provide a non-metallic insert (f.e. plastic) with the required dimensions of the metal free zone: 3 x Ø of the sensor.

Switching Distance S
The switching distance is the distance where an electrical stale change is induced in the prox. switch when a target is close enough to be recognized by the proximity device's sensor circuity (ie: test method according to EN 50010).
Nominal Switching Distance Sn
The nominal switching distance is defined as the distance which does not include variations due to temperature and voltage fluctuations, mounting media, and manufa-cturing tolerances (ie: the design para-meters).
Effective Switching distance Sr
The effective switching distance for an inductive proximity switch is that distance which accounts for permissable production tolerance variations at defined voltage and temperature conditions (±10% of Nom. Switching Distance). 0,9Sn <  Sr < 1,1Sn
Usable Sensing Distance Su
The usable sensing distance is the distance of a proximity switch which is measured under permissable temperature and voltage conditions.
0,9Sr < Su < 1,1Sr
Working Distance Sa
The working distance is the distance which guarantees the safe operation of the prox. switch under established temperature/vol-tage conditions. It is definded  0 to 81% of the Nominal Sensing Distance  (ie: the smallest Usable Sensing Distance).
0 < Sa < 0,9X0,9 Sn
Target Considerations
For all published switching distances, a standard square target is made from 1mm  thick steel material (S235JR) with a side length "m" equal to the Ø "d" of the sensor's active surface. The use of other metals will have the effect of reducing the switching distances. The following is a list of common materials and their calculable correction factors:
Stainless Steel        ca. 0,8 x Sn
Aluminium           D ca. 0,4 x Sn
Brass              D     ca. 0,5 x Sn
                            (is alloy dependent)
Copper              D    ca. 0,3 x Sn
Spherical or smaller targets will result in a smaller working distance and hence, the Normal Sens. Distances will be reduced. On the other hand, thin foils or large targets will slightly increase the sensing distance. Sn=EN 50010 (DIN VDE 0660).
Repeatability R
The repeatability of the usable switching distance is measured by performing two consecutive measurements within 8 hours at a housing temperature of 15° to 30 °C. During this test period, the supply voltage variation must not exceed ± 5%.
Switching Hysteresis (H)
The switching hysteresis is the difference between the switch activation distance with the target approaching the active surface of the proximity switch and the deactivation distance when the target is moved away from the sensing surface.
Switching Frequency f
The switching frequency of a device is defined as the maximum number of tar-gets that can be sensed in one second. The switching frequency depends upon the size of the proximity switch's sensing surface. In comparison, A. C. models have inherently lower switching frequencies than D. C. models.
Supply Voltage VB
The supply voltage is the nominal power supply voltage that the specified proximity switch should have on its appropriate terminals. The selected applied device supply voltage should not deviate from the permitted ripple.
Ripple VW
Ripple is the A.C. voltage, peak to peak, that is superimposed on the supply voltage (VB).
Forward Voltage Drop VD
The forward voltage drop VD is the voltage across the proximity switch's output when it is in the conductive state.
Switching Capacity CA
The switching capacity is the maximum parasitic load capacity that the D. C. proxi-mity switch outputs can handle.
Inrush Current IK
The inrush current is specified as the maximum current that can occur the moment the load is activated.
Load Current IA
The load current, when specified, is the maximum current, that the output of proximity switch can accomodate when it is in the on state.
Minimum Holding Current IQO
The minimum holding current specificat-ions is usually used in respect to A. C. mo-dels only. This specifies the minimum current that has to be applied to the output of the proximity switch for proper operation.
Leakage Current IQK
The leakage current refers to the residual current that flows through the output stage of the proximity switch when the device is in the non-conductive state.
Quiescent Current IO
This current is specified as the power supply current that is discharged to the load when the switch is locked.
Residual Current IR
Means the current that is discharged to the load when the switch is locked.
Short Circuit Protection DC-Sensors
Apart from a few exceptions, all D. C. prox. switches incorporate short circuit pro-tection. Upon removal of the short circuit across the proximity switch, the output resumes its normal operation. The output of these short circuit proof models is constantly monitored by a unique circuit. When a short circuit or overload occurs, this safety circuit is activated. Depending upon the nature of the overload problem, the output of the proximty switch is pulsed.
In addition, the short circuit/overload protection is resistant to:
    • Interference pulses from noisy indus-
D trial networks
    • Capacitive effects caused by long
D cable length
    • Charging and discharging of capacitive
D loads, Turn off protection
Protection Reverse Polarity
Any exchange of the proximity switch's out-put leads with the power supply leads and the signal leads will not damage the electric circuitry. The feature is included in all D. C. models. It is worth nothing, however, that damage can occur when the output of a non-short-circuit protected device is con-nected to the power supply terminals.
Interrupted Supply
Output Protection
The proximity switch output is disabled when the cable connections are broken.
Switching Current Ranges
All devices are capable of switching a wide variety of load currents. They can drive integrated circuits and sensitive relays as well as higher loads such as contactors and electric solenoids.
LED Models

The LED indicates the state of the proximity switch's output.

Please note:

Errors/printing mistakes excepted. We reserve the right to change the technical details without notice.Only the customer knows all the conditions / influencing factors. He is therefore in principle required to qualify our equipment for his proposed application itself. A legally binding assurance of certain properties or suitability for a specific application can not be derived from our datas. Applications are inadmissible when safety of persons depends on the function of our switches/sensors.

Capative Sensors


  Capacitive Working Method EN 60947-5-2 (DIN VDE 0660)
  The active surface of a capacitive sensor is generated by two metallic electrodes. The sensor is triggered when an object appro-aches the junction surface and thus enters the electric field of the electrodes. The resulting increase in coupling capacity causes the oscillator to vibrate. The oscillation amplitude is aquired by an analy-zing system and converted into a switch signal. Capacitive sensors can be triggered by conductive as well as non-conductive objects. On account of their high conductivity, metal control elements will allow for increasing the switching distances. When scanning organic materials, such as grain or wood, the switching distance depends to a great extent on the water content of the material. The reduction factor existing with different metals (as in the case of inductive sensors) does not have been taken into account. The capacitve proximity sensor sensitivity is continuously adjustable on a poti.
  Housing Material
  Capacitve proximity switches are available in the same housing material like the inductive proximity switches.
  Mounting in Metal
  A free space at the junction surface has to be allowed for in the case of capacitive proximity switches installed non-flush in metal.
  Switching Distance
  The switching distance can be continuously adjusted on a poti. No work tolerances or anomalies owing to external influences (such as tension, temperature, moisture and mounting conditions) are allowed for in this distance.
  Gauging Plate
  Basic alignment of the capacitive sensor is made by means of an earthed metal gauging plate with an edge length of 3 x d.
  Sampling Frequenzy
  Minimum 10 switch cycles/second.