These basic principles apply to all our precision switches. The specific characteristics of each model are given in more detail in the relevant product sections.
Introduction
Our microswitches are high-precision, snap-action microswitches and these are the main features for which they are notable :
■ High ratings but small dimensions
■ Very short travel
■ Low operating force
■ High reliability of travel and force values
■ Long life
■ Large range of actuators for easy adaptation to the most varied applications
Microswitch construction
Single-pole changeover microswitch (e.g. “V3” 83 161)
Double-pole changeover microswitch (e.g. 83 132 0)
The NO and NC circuits must both be of the same polarity.
Mechanical characteristics
Terminology - Forces - Positions - Travel
Graphs of forces vs. travel
Mechanical characteristics
? Changeover time
This is the time taken by the mobile contact when moving from one fixed contact to another until it becomes fully stable (contact bounce included).This time is a function of the contact gap, the mechanical characteristics of the snap action and the mass of the mobile element.
However, thanks to the snap-action mechanisms employed, the time is largely independent of the speed of operation.
It is normally less that 20 milliseconds (including bounce times where less than 5 ms).
? Mechanical durability
This is an average value indicating the purely mechanical performance of a microswitch when not subject to any electrical load. It may be useful for evaluation purposes in cases where the power levels involved are very low and the electrical life is thus close to the mechanical life.
? Maximum speed and rate of operation
Our microswitches will work at speeds of operation varying over a very wide range : normally from 1 mm/min to 1 ms.
The maximum rate of operation with a low electrical load may be as high as 10 operations/second.
? Mounting - Operation
? To conform to the leakage paths and air gaps in the standard EEC24
- EN/IEC 61058 - EN/IEC 60947:
■ An insulation pad must be inserted between the microswitch and the fixing surface if the latter is metal.
■ Manual operation of a metal actuator must only be carried out with the help of a secondary actuator made of insulating materials.The installer must ensure adequate protection against direct contact with the output terminals.
? Fixing - Screw torque
? Unless otherwise indicated in the mechanical characteristics table, the torque required for the fixing screws must conform to the following values :
Environmental conditions
? Resistance to shocks and vibrations
Resistance to impact and vibration depends on the mass of the moving parts and on the forces holding the contacts together.
Generally speaking, for a microswitch without an actuator :
■ Vibration >10 G 10 at 500 Hz
■ Impact > 50 G 11 ms 1/2 sine
Further information on request.
? Ambient operating temperature
The maximum and minimum temperatures at which the mechanical and electrical characteristics of the microswitch will remain substantially unaltered.
? Degree of protection
Under the IEC 529 or NFC 20010 classification scheme, standards employ an IP code to define the degree or class of protection which electrical equipment provides against access to live components, the entry of solid foreign bodies and ingress of water.
Under this classification, our microswitches come within the following
categories :
■ Plain microswitches = IP 00
■ Protected microswitches = IP 40 with isolated connection
■ Sealed microswitches = IP 66 or IP 67
Dielectric characteristics
? Current rating
This is the current the microswitch is capable of making and breaking,which forms the basis for the life tests.
?Thermal rating
This is the current the microswitch will withstand when not being operated,for a temperature rise of not more than 60°C.
? Switch rating
AC voltages : see the current rating
With DC voltages the switch rating is very much dependent on the voltage,the contact gap and the nature of the load being switched. There is a risk of prolonged or indeed permanent arcing if the following limits are exceeded:
? Operating curves
These indicate the electrical life of the microswitches, under standard conditions (20°C, 1 cycle/2 seconds), by showing the number of switching operations which can be performed with given types of load.
Note : for sealed products and D.C. ratings, the operating rate is 1 cycle/6 seconds.
Circuit types
? Resistive circuit
For a circuit with alternating voltage, this is in phase with the current : Cos ? = 1.
? Inductive circuit
A circuit of this type with direct current is characterised by a time constant. An inductive circuit, with alternating voltage, for example, incorporating a motor (cos ? < 1) can cause current surges up to 6 times the nominal current. For certain switches, we give electrical endurance curves with L = 5 ms in DC R and cos ? = 0.8 in AC.
? Lamp and capacitance circuit In this case, currents at the closing of the circuit have high value, up to 10 times the normal rating.
? Internal resistance
This consists of the intrinsic resistance (fixed) of the parts carrying current and the contact resistance (variable). Close to the tripping point and release position, the force holding the contacts together drops considerably and this may cause a significant rise in internal resistance.
? Insulation resistance
The insulation resistance of the microswitches is generally greater than 50 000 MΩ measured at 500 V DC.
? Dielectric strength
The dielectric strength of our microswitches is generally better than :
■ 1500 volts between live parts and earth
■ 1000 volts between contacts
■ 600 volts between contacts for microswitches
whose contact gap is less than 0.3 mm.
Contact materials
? Choice of contact material
To choose the best material for the contacts there are various factors to be considered :
■ the current and voltage levels
■ the type of load
■ the number of operations
■ the switching frequency
■ the environmental conditions
? Contacts for general-purpose use
Our microswitches are normally fitted with silver contacts. These are suitable for the majority of applications and provide the best compromise between electrical performance, thermal performance and life.
? Contacts for low-power circuits
U < 10 V and/or I < 100 mA
The contacts used in this case are plated with gold (or a gold alloy) for good reliability even in corrosive atmospheres.
? Contacts for special applications
We can supply special contacts suitable for particular applications, such as :
■ Ag CdO contacts for very high drawn currents
■ Cross gold-plated Ag Ni contacts which allow a very wide range of applications to be covered by a single type of microswitch.
Electrical recommendations
? Inductive circuits
To increase the life of contacts and their DC rating, arcing on opening can be reduced by using the following circuits :
?Very low-power circuits
In very low-power circuits (I > 1 mA, V ≤ 5 V), switching is highly sensitive (to the atmosphere, pollution). If the supply is powerful enough, adding a passive resistor to increase the current broken by the microswitch to a few milliamps will substantially improve reliability of operation.
R - Load resistance
C - Very low current load
Methods of actuation
? Methods of actuation
Force should preferably be applied to the device to be directly operated- the plunger - along its axis. However, the majority of our microswitches will accept skewed operation provided the angle of application is not more than 45°.
The device used to apply the force must never hamper the travel of the plunger to the tripping point (TP). It must under all circumstances move the plunger through at least 0.5 times the overtravel (OT) quoted. Steps must also be taken to see that it does not cause the OL or MOF quoted to be overrun or exceeded.
? Operation by actuator
When operation is by a roller lever, force should preferably be applied in the direction shown on the left.
Where the movements involved are fast, the ramp should be so designed as to ensure that the operating device is not subjected to any violent impact or abrupt release.
Quality
Crouzet undertakes a pro-active quality policy adapted to our different markets of which the objectives are:
■ To actively contribute to the success to our clients
■ To ensure the perennial development of the company and the brand by achieving global performance (social, economic, product and service offer) in the fi eld of environment and legislation.
?This quality implies:
■ Mobilisation and dynamic behaviour by the entire staff
■ Achieving results and respecting our commitments
■ Sharing our policies with our partners (clients, suppliers…)
?This quality is based on a series of ongoing actions:
■ Focusing on the preventative
- Quality starts from the understanding of the clients needs in order to work out the specifi cations where Crouzet acts as expert advisor.
- Quality is pro-active in actions for progress
- Quality ensures the systematic exploitation of feedback experience, methods and quality tools.
Standards - Approvals
Our microswitches are designed according to international recommendations(IEC), American standards (UL) and/or European standards (EN).Proof of compliance with these standards and recommendations is demonstrated by
■ the manufacturer’s declaration of conformity (drafted in accordance with the ISO/IEC 22 guidelines), or
■ approval granted directly by an accredited body, or by application of the CCA (Cenelec Certification Agreement).
More detailed information on the approval for a particular type of microswitch can be obtained on request.
Rules and regulations
? EC directives
Our microswitches are compatible with European Community technical directive (Low Voltage) 73/23 and can be used within the framework of Machinery directive 83/392.
? Environmental protection ISO 14001
The modern concept of protection of the environment is an integral part of the manufacture of our microswitches, from product design through to packaging.
