Common Features of Electromechanical Switches Switching systems F F Lag between NC and NO Lag Switching elements lie at the heart of all contact function (hysteresis) electromechanical switching devices and must correspond to the respective applica- tion. Essentially there are two basic types of switching system that differ in terms of S their mechanical design and consequently S their scope of application: 2) 1) l Slow-action contacts l Snap-action contacts Slow-action contacts l On actuation, the normally-closed and Fig. 2 shows the contact force during the Fig. 3 shows the contact force during the normally-open contact functions corres- switching cycle of a slow-action contact switching cycle of a snap-action contact. pond to the movement of the impact pin 1) with overlap. Changeover point in forward travel l The approach speed controls the contact 2) Changeover point in reverse travel opening (closing) time l Large distance/actuating travel between Snap-action contact Switching diagram normally-closed and normally-open con- tact function l On actuation, the normally-closed con- The switching diagram describes the l The switching points are identical in tact function is immediately followed by function of the switching device in detail. forward and reverse travel the normally-open contact function It combines the mechanical input variables l In this configuration there is no overlap that act on the contact system via the actu- of the NC/NO contacts. The switch pro- ator with the electrical output variables. The vides a distinct OR-function. user can deduct the following information l The changeover accuracy is not depen- F Lag between NC and NO from the switching diagram: dent on the approach speed contact function l Consistently effective suppression l Mechanical input variables of DC arc (force, travel, torque, angle) l Reliable contact-making also for l Electrical contact-making in forward extremely slow approach speeds and reverse travel S l The snap mechanism triggers the l Terminal designation full opening width of the contact on l Point at which positive opening reaching the changeover point is achieved l Due to the force reversal in the mecha- l Type of contact system nical system, a different switching point occurs in forward and reverse travel. The lag is referred to as hysteresis. 2N 0 6.5Ncm 0 Fig. 1 shows the contact force during the 1 10 switching cycle of a slow-action contact. 1.8 Overlap 35 3 55 l The switching principle of slap-action contacts makes overlapping of the NC/ 12,5N 6 75 6Ncm NO contact function possible. The term overlap refers to the area, in which both Slow-action contact Snap-action contact the normally-closed contact as well as the normally-open contact are closed in Contact closed connection with a changeover switch Contact open with delay. 12 11-12 23-24 21-22 13-14 13-14 21-22Contact designation Enclosures Safety switches In accordance with DIN 50013 and DIN 50005 Limit switches are supplied either in a moul- The scope of application for limit switches the terminal designations of the contact ele- ded enclosure or a metal enclosure. Which has changed over time. Whereas limit swit- ments are always make up of two digits. material is to be selected for a specific appli- ches were previously used for the purpose cation depends on the ambient conditions, of detecting end positions, today they are The contact rows are numbered consecuti- the location as well as several other factors. increasingly assuming functions designed vely with the allocating digit (1st digit) in to protect persons and products in machine, actuation direction. Contacts of a switching Moulded limit switches provide protective equipment and plant construction. element that belong together have the insulation and are resistant to many aggres- same allocating digit. sive chemicals and liquids. The formation of The BERNSTEIN range of safety switches condensation water in moist environments offers the right solution for the most diverse The second digit is the function digit that with extreme temperature fluctuations is applications in many branches of industry. denotes the type of contact element. significantly reduced on moulded enclosures. Particularly when it comes to safety, users appreciate the fact that they are able to 12 Normally-closed contact In insulation-enclosed switches the switch- procure all required safety switches and ing elements are integrated directly in the receive professional advice from one source. 34 Normally-open contact moulded enclosure and are therefore not 56 Normally-closed contact with replaceable (complete switching devices). The decisive factors governing the selection delayed opening of safety equipment include the ambient 78 Normally-open contact with Metal-enclosed limit switches are able to conditions, installation situation and risk delayed closing withstand high mechanical loads, they analysis. can also be used wherever hot metal chips and sparks occur and are resistant to many A switching device that can be used for Protection class solvents and detergents. The switching safety functions is identified by the standard- The protection class of an enclosed device elements in metal-enclosed switches are ised symbol conforming to EN 65000-41 denotes the degree of protection. The de- often integrated in the metal enclosure as and EN 65000-42. The switches can, of course, modular built-in switches. The enclosure also be used for pure position monitoring gree of protection includes the protection has a VDE-compliant connection for the purposes. of persons against contact with parts under voltage and the protection of equipment PE conductor. against the infiltration of foreign bodies Safety switches are divided into two cate- and water. BERNSTEIN standard enclosures gories, Type 1 and Type 2. The difference is in the actuating elements which are com- mainly correspond to protection classes pletely integrated in the enclosure in Type 1 IP65 and IP67. Higher protection ratings are also available for individual customer solu- and separated from the switching element tions. In accordance with DIN EN 60521 in Type 2. (IEC 529), the numerals used in the protec- tion rating denote the following: 1st digit Degree of protection against con- tact and infiltration of foreign bodies 2nd digit Degree of protection against infiltration of water Example IP65: Type 1 Type 2 6 = l Complete protection against contact with components under voltage or with internal moving parts l Protection against dust infiltration 5 = l A water jet directed from all directions at the device must not have damaging effects l Protection against hose water 13