Reed Switch and Reed Sensor Definitions

• Ampere Turn (AT)

  The product of the number of turns of wire in an electromagnetic coil winding and the current in amperes passing through the winding. This is a direct measure of a reed contact's sensitivity.

• Bounce

  Intermittent opening and closing of closed contacts or closing and opening of open contacts, usually implying the motion resulting from contact impact.

• Bounce Time (in milliseconds)

  Time taken for a bounce.

• Breakdown Voltage

  The voltage which may be applied between insulated parts of a reed contact without damage, arcing, breakdown or causing excessive leakage.

• Carry Current (in Amps)

  The maximum current that can be applied to an already closed contact

• Chatter

  The undesired intermittent closure of open contacts or opening of closed contacts. It may occur either when the reed contact is operated, released or when subjected to external shock or vibration.

• Coercivity

  Demagnetization force required to reduce polarization or induction to zero.

• Contact

  The current-carrying parts of a reed contact that engage or disengage to close or open electrical circuits

• Contact Gap

  The distance between mating reed contacts when the contacts are open.

• Contact Rating (in Watts)

  The maximum power, a reed contact can switch.

• Curie Temperature

  Temperature at which a magnet is totally demagnetized.

• Differential

  The difference between operate AT and release AT. This is also expressed in % as (OAT-RAT)/OAT %

• Drop Out (DO)

  See Release AT.

• Dwell (for Form C and D type contacts)

  For form C contacts, it is the difference, in AT, between the closing of the NO contact and the opening of the NC contact, and for form D contacts, is the difference, in AT, between the opening of the NC contact and the closing of the NO contact.

• Form A

  A normally open type of reed contact.

• Form B

  A normally closed type of reed contact.

• Form C

  A change-over type of reed contact where break happens before make.

• Form D

  A change-over type of reed contact where make happens before break.

• Form E

  A latching, or bi-stable type of contact, which stays in the last energized state, without the need for maintaining the field.

• Hysteresis

  See differential.

• Insulation Resistance

  The electrical resistance measured between insulated terminals

• Omni-polar

  This type of device fully functions with either pole of a magnet.

• Operate AT (OAT)

  The measured value, in AT, at which a reed contact closes. This is valid for the closing operation of form A, B, and E type reed contacts, and the change over operation from the normally closed contact to the normally open contact for form C and D type reed contacts.

• Operating Temperature

  The temperature range over which the reed contact will meet all specified operating parameters.

• Operate Time

  The time interval from coil energization, to the closing of the reed contact. Where not otherwise stated, the functioning time of the reed contact in question is taken as its initial functioning time, not including contact bounce.

• Over-drive (in AT)

  The percentage of AT given above OAT, before measurement of CR.

• Pull In (PI)

  See Operate AT.

• Re-closure (RC)

  The closure which occurs after further energization of an already energized, normally closed reed contact in open condition. This is applicable to form B type reed contacts and to the un-latching operation of form E types.

• Reed Switch

  A reed switch is a passive device consisting of two reed contacts sealed inside a glass tube which operates when brought near a magnetic field.

• Reed Sensor

  A reed sensor is a device built using a reed switch with additional functionality like ability to withstand higher shock, easier mounting, additional intelligent circuitry, etc.

• Release AT (RAT)

  The measured value, in AT, at which a reed contact opens. This is valid for the opening of form A, B, and E type reed contacts, and the change over from the closed normally open contact to the open normally closed contact for form C and D type contacts.

• Release Time

  The time interval from coil de-energization to the opening or change over of the reed contact. Where not otherwise stated, the functioning time of the reed contact in question is taken as its initial functioning time, not including contact bounce.

• Remanance

  Residual induction in magnet material after being magnetized to saturation.

• Resonance Frequency (in Hz)

  The maximum operating frequency that a reed contact can withstand, after which it chatters, or starts sympathetic vibration.

• Saturation

  Magnetic saturation exists when an increase of magnetization applied to a reed contact does not increase the magnetic flux through.

• Static Contact Resistance (CR)

  The electrical resistance of closed reed contacts, as measured terminal to terminal,at their associated terminals.

• Switching Frequency (in Hz)

  The maximum frequency at which a reed contact can operate

• Switching Voltage (in Volts)

  The maximum voltage a reed contact can switch.

• Switching Current (in Amps)

  The maximum current a reed contact can switch.

• Thermal EMF

  The EMF generated by a reed contact when the reed contact unit is subjected to a temperature differential. For most reed switches, this is in the region of 40 micro volts per degree C.

• Variable Contact Resistance (VCR)

  The difference between lowest and highest static CR readings out of a set consequent test cycles.