FAQ / Technology

General questions

• Are the products RoHS and REACH compliant?

  Almost all of our products are RoHS and REACH compliant.
  There are only a few exceptions, such as mercury relays or some special sensors.
  However, these are only used in special applications.

• What is reed technology?

  Reed technology enables contactless switching of an electrical signal or voltage with the aid of a magnetic field. A defined external magnetic field acts on a special ferromagnetic switching contact, also known as a reed switch or reed contact. This magnetic field is usually generated by a permanent magnet or a coil. Products based on this technology are also known as reed sensors.

  Advantages of reed technology (reed sensors):

  • Contactless, low-wear switching process
  • Long service life
  • High switching frequency
  • Cost-effective alternative to electronic switch
  • maintenance-free

• Which housing material should I choose?

  The correct choice of housing material is crucial for the longevity of the product. The material selected must permanently protect the components (reed switches) inside the sensor to ensure proper functioning.

  Selection criteria :

  • Minimum and maximum ambient temperature
  • Medium in which the sensor is used
  • Maximum pressure in the medium
  • Mechanical stress

  Possible housing materials:

  • Metal: Stainless steel, brass
  • Plastic: PA, PC, PP, POM, others on request

  We will be happy to advise you on the selection of the optimum enclosure material for your application.

• Which protective circuit makes sense?

  When switching alternating current, an RC element must be connected in parallel with the reed switch and thus in series with the load.

  When switching direct current, a freewheeling diode must be connected in parallel with the load. The polarity must be set so that the diode blocks at the normal operating voltage and short-circuits the voltage spike that always occurs in the opposite direction when the reed switch is opened.

  Capacitive loads
  Capacitive loads and lamp loads cause increased inrush currents, which can lead to faults and even welding of the contacts. When switching charged capacitors (e.g. also cable capacitors), a sudden discharge occurs, the intensity of which depends on the capacitance and the length of the lead to the switch, which is to be regarded as a series resistor. The discharge current peak is largely reduced by a series resistor to the capacitor. It should be as large as possible in order to limit the discharge current to a permissible value.

  Incandescent lamp filaments have a resistance that is around ten times lower when cold, i.e. when not switched on, than when glowing. This means that when switched on, even if only briefly, a ten times higher current flows than in the glowing, static state of the lamp. This 10-fold inrush current can be reduced to a permissible level by a current-limiting resistor connected in series. One possibility is to connect a resistor in parallel to the reed switch, which continuously preheats the lamp filament in the switched-off state to such an extent that it just does not glow.

• How do external magnetic fields influence the function?

  External magnetic fields can lead to malfunctions or permanent changes. Magnetic shielding in reed relays can shield the reed switch from these fields.

  Reed technology is based on a reed switch that switches by magnetic influence. Our products are precisely matched to this interaction. An additional external magnetic field can influence this and lead to malfunctions. Therefore, keep sufficient distance from magnetic fields, e.g. transformers, motors, ...

• What defines the IP protection class?

  The IP protection class defines the suitability of electrical equipment for different environmental conditions. The exact degree of protection is determined with the help of 2 code numbers (IP codes). Details can be found in the table below.

  1st digit defines protection against foreign bodies and contact

   

  Digit	Protection against foreign bodies	Protection against contact
  0	No protection	No protection
  1	Protected against solid foreign objects with a diameter ≥ 50 mm	Protected against access with the back of the hand
  2	Protected against solid foreign objects with a diameter ≥ 12.5 mm	Protected against access with a finger
  3	Protected against solid foreign bodies with a diameter ≥ 2.5 mm	Protected against access with a tool
  4	Protected against solid foreign bodies with a diameter ≥ 1.0 mm	Protected against access with a wire
  5	Protected against dust in damaging quantities	Complete protection against contact
  6	Dustproof	Complete protection against contact

   

  2nd figure defines the protection against water

   

  Digit	Designation
  0	No protection
  1	Protection against dripping water
  2	Protection against dripping water when the housing is tilted up to 15°
  3	Protection against falling spray water up to 60° against the vertical
  4	Protection against splashing water on all sides
  5	Protection against water jets (nozzle) from any angle
  6	Protection against strong water jets
  7	Protection against temporary submersion
  8	Protection against permanent submersion

Questions about reed switches

• How does a reed switch work?

  The reed switch is a magnetically actuated switch in a small glass body. It consists of two ferromagnetic reeds (with an iron-nickel alloy) that are hermetically sealed in a glass tube. These 2 switching tongues overlap minimally and are only a few micrometers apart. If a magnetic field approaches the switching tongues, they attract each other and then close the contact. If the magnetic field weakens again (by removing the magnet), the contact opens again.

   

  Reed contacts can be used in almost all environmental conditions due to the materials used and the hermetically sealed design. The two switching tongues in the contact area are coated with a very hard metal, usually rhodium or ruthenium (also tungsten and iridium for special switches). This design ensures a long service life and reliable operation.

• What are the advantages of a reed switch?

  • Contactless switching via external magnetic field

  • Cost-effective solution for reliable switching tasks

  • No separate power supply required

  • Long service life of several hundred million switching operations

  • No minimum switching current required (exceptions for special contact materials, e.g., tungsten)

  • High switching reliability thanks to reproducible and stable contact

  • Very low contact resistance of typically 70–200 mΩ when new

  • Can be used in potentially explosive and aggressive environments, as the contacts are hermetically sealed

• What is the service life of a reed switch?

  The achievable service life is highly dependent on the load. With pure signal loads, several hundred million switching cycles are possible. With higher loads, such as mains voltages or high currents, the service life is typically between several tens of thousands and over a million switching cycles.

  To prevent premature aging, the same contact protection measures should always be used as for conventional switching contacts, for example varistors, diodes, or RC elements.

• What types of contact are there?

  Normally open (Form A)
  In the rest position, the reed contact is open. When a magnet is brought close to the switch, the paddles move toward each other and the switch closes. When the magnet is removed, the reed contact opens again.

   

  Normally closed (Form B)
  A reed contact that is closed in its resting position opens when a magnet is brought close to it and closes when the magnet is removed again.

   

  Changeover switch (Form C)
  A so-called SPDT (single pole double throw) is a changeover contact that switches from the idle contact to the working contact when a magnetic field is applied.

• What does the AW (AT) value mean for reed switches?

  AW stands for ampere turns and describes the magnetic sensitivity of a reed switch. The English term for this is AT = ampere turns.
  The AW value is determined in a defined test coil in which the reed switch is positioned centrally. When voltage is applied to the coil, a current flows and generates a magnetic field.

  By gradually increasing the current until the reed switch closes, you obtain the pull-in value, which is the product of the current and the number of coil turns.
  The drop-out value is determined by subsequently reducing the current until the reed switch opens again.

• What different types of reed switches are there?

  The reed contact is available in many different versions. The following parameters differ:

  Switching capacity
  This is in the range of 0.1 to 30 W. Even a brief overload leads to failure. It must be ensured that none of the specified values (voltage, current) are exceeded, even briefly. Caution with capacitive or inductive loads.

  Switching current
  This is the maximum permissible current when the reed contact closes. The higher the current, the greater the switching arc when closing and opening. If the current is too high, the contacts may stick together (weld), as a result of which the function is no longer guaranteed. Capacities of the connected circuit also have a negative effect on the service life of the reed contact. With relatively high switching signals, the current should be limited in the first 50 ns. From 50 V and 50 pF, a permanent influence on the reed contact can already occur.

  Transport current
  This specifies the maximum permissible current via the already closed contacts. This is higher than the switching current, as the contacts are already closed.

  Switching voltage
  This is the maximum permissible voltage (DC or AC) that the contact may switch (even for a short time). This ranges from 100 V to 10,000 volts.

  Insulation resistance
  The value measured across the open reed contact is typically in the range of¹⁰⁹ Ω to ¹⁰¹⁴ Ω. This good insulation causes only the smallest leakage currents from femto to pico amperes. Test equipment that requires high-impedance switching between several inputs can therefore be realized.

  Contact capacitance
  This is the capacitance between the contacts when the switch is open. The values are approximately in the range of 0.1...0.3 pF. The low contact capacitance is a special feature of reed contacts. This allows high-impedance AC voltage signals to be transmitted with low crosstalk.

  Pull-in sensitivity
  This value specifies the closing point of the switch. It is usually specified in ampere-turns (AWan). A defined measuring coil is used to determine this value. For this purpose, the current of the measuring coil in which the reed contact to be measured is located is increased up to the switch-on point. The determined current value is then multiplied by the number of turns of the coil = pick-up sensitivity. The specification is generally valid for 20 °C.

  Switching hysteresis
  is the ratio in % between the switch-on and switch-off points

  Closing time (incl. bounce time)
  This is the time required to close the contact (until after the end of the bounce). Most reed contacts have a closing time of 100 - 500 µs.

  Release time
  This is between 0.05 and 2ms, depending on the reed contact.

  Switching speed
  up to 300 Hz

  Vibration resistance
  The mechanical vibration resistance is in the range between 10 and max. 30 G.

  Temperature range
  approx. -20°C ... +150°C , special types also with extended temperature range

• Which electrical limit values must be observed?

  The reed switches (and therefore all products containing them, such as reed sensors, float switches, etc.) may only be operated within the electrical limit values specified in the data sheet (switching current, switching voltage, switching capacity). Exceeding one of these limit values, even briefly, can lead to a reduced service life or even failure.

  The values specified in the data sheets apply to purely resistive loads! However, the loads are usually fitted with inductive or capacitive components or lamp loads are switched. This can result in inrush currents that are more than 10 times the operating current. In all these cases, the reed contacts must be protected against the occurrence of voltageand current peaks in order to prevent rapid wear or premature failure. See the section on protective circuitry.

• What is the maximum switching capacity?

  The max. switching capacity is the product of switching current and switching voltage. The max. value depends on the selected reed contact.
  For alternating current values, the current and voltage must also be multiplied by the power factor cos φ.
  The individual limit values of the sensor must not be exceeded under any circumstances, not even briefly.
  This is particularly important for inductive or capacitive loads.
  A current of more than 10 times the rated current (operating current) can flow at the switch-on or switch-off moment.
  These max. peaks must also not exceed the limit values. Use a protective circuit for the reed sensor to prevent destruction or malfunction. We will be happy to help you.

• What is the switching hysteresis?

  The switching hysteresis is the differential distance between the switch-on and switch-off points. It mainly depends on the type of reed contact and is approx. 1 to 4 mm. A hysteresis is necessary so that the reed switch switches reliably, otherwise it would "flutter" at the switching moment.

  Example:
  The reed contact switches on when the magnet approaches at 10 mm.
  The reed contact switches off when the magnet moves away at 12 mm.

• What is the switching point accuracy?

  Magnetic switches (proximity switches) have a very high repeat accuracy of the switching point.
  It is in the range of approx. 0.02 mm under constant ambient conditions.
  This ensures that the sensor always switches at the same position.

• What is the response and release time/switching speed?

  When switching on:
  The response time (including bounce time) is between 0.6 and 3 ms, depending on the reed contact size.

  When switching off:
  The release time is between 0.05 and 2 ms, depending on the reed contact size.

  
  Switching speed:
  For magnetic switches with reed contacts up to 300 Hz, depending on the type and size of the reed contact.
  For switches with Hall element up to 100 kHz, depending on the design.

Questions about float switches

• How does a float switch work?

  The float switch works with a float that contains an integrated magnet to monitor the fill level of a container. The float moves up and down on a riser pipe (slide pipe) with the water level. A reed contact is positioned inside the riser pipe at the desired fill level. As soon as the float reaches this point, the reed contact is activated without contact by the magnetic field of the float.

• Which housing material should I choose?

  The correct choice of housing material is crucial for the longevity of the product. The material selected must permanently protect the components (reed switches) inside the sensor to ensure proper functioning.

  Selection criteria :

  • Minimum and maximum ambient temperature
  • Medium in which the sensor is used
  • Maximum pressure in the medium
  • Mechanical stress

  Possible housing materials:

  • Metal: Stainless steel, brass
  • Plastic: PA, PC, PP, POM, others on request

  We will be happy to advise you on the selection of the optimum enclosure material for your application.

• How much current does a float switch/reed sensor consume?

  As long as the switching contact (reed contact) in the float switch is open, no current flows. No energy is consumed. Current only flows when the contact is closed.

• How are float switches installed?

  They are usually mounted in the lid of the container. Other options are in the base or on the side of the tank. There are float switches that are mounted from the inside and also types that are mounted from the outside.

• How many switching points does a float switch have?

  Almost any number of switching points can be installed. One reed switch is required for each switching point.

Questions about reed sensors

• Comparison of Hall sensor with reed sensor

  Description	Hall sensor	Reed sensor
  Sensitivity	> 10 Gauss	> 5 Gauss
  Switching distance	up to 20 mm	up to 40 mm
  Power supply	permanently necessary	none
  Hysteresis	approx. 75%	depending on application
  Switching capacity	a few milliwatts	up to 100 watts
  Contact resistance	> 200 Ohm	0.05 Ohm
  Output capacity	100 pF	0.2 pF
  Insulation resistance	106 Ohm	1012 Ohm
  ESD sensitivity	Yes, requires external protection	No
  Working temperature	0 - 70 °C	-55 - 150 °C

• What is the switching distance for reed sensors/proximity switches?

  The switching distance is the distance at which the reed switch (proximity switch) is actuated by approaching the magnet. The length of the switching distance depends on the field strength of the magnet and the sensitivity of the reed contact.

  The switching distance is usually between 1 and 30 mm, depending on the design of the system.

   

Questions about reed relays

• Comparison of reed relay with mechanical relay

  Description	Reed relay	Mechanical relay
  Service life	109 Switching operations	106 Switching operations
  Switching time	0.2 - 1 ms	> 5 ms
  Switching voltage	Femto-Volt up to 10kV	up to 4kV
  Power consumption	approx 5 mW	approx. 50 mW
  Switching current	up to 3A	up to 40 A
  Insulation resistance	up to 1014 Ohm	up to109 Ohm

• What are the operating voltages of Red relays?

  The reed relay excitation coil is usually operated with DC voltages of 5 V, 12 V, or 24 V. These are the standard voltages for many electrical circuits and circuit boards.

• What voltages can reed relays switch?

  The maximum switching voltages of reed relays are mainly in the range of 100 volts to 1000 volts. However, there are also special types (high-voltage relays) that can switch up to 10 kV. In this case, however, the maximum switching capacity of the relay must always be taken into account.

Questions about magnets

• Does a magnet retain its magnetization over the long term?

  With good magnetic material, a suitable environment, and proper use, the magnetic properties typically remain stable for several decades, often 50–100 years, especially with SmCo, Alnico, and ferrite.

  NdFeB is the most powerful, but its service life is more dependent on temperature and corrosion.

• What are the different properties of magnetic materials?

  Properties	Ferrite	AlNiCo (aluminum-nickel-cobalt)	SmCo (Samarium-Cobalt)	NdFeB (neodymium-iron-boron)
  Magnetic force	low	medium	high	Very high
  Operating temperature	up to 300°C	up to 500°C	up to 250°C	up to 80°C
  Corrosion resistance	high	good	high	low (will be coated)
  Costs	favorable	moderate	very expensive	expensive

   

  Permanent magnets are used in many of our products. The magnet material used should be matched to the respective application. Various operating conditions must be taken into account in order to select the suitable material for the magnet.
  Magnets react differently to temperature, shock, vibration and external magnetic fields, depending on the material. This can have an influence on the magnetic force and long-term stability. It is therefore extremely important to select the right magnet. We are happy to help you with this.