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Typical Switch Applications
Domestic Appliances- There are few other fields of switch application where compliance with official approvals is of such importance as it is in domestic appliance applications. In the U.K. the whole appliance must carry British Electro-technical Approvals Board (BEAB) approval to BS3456, and this Specification stipulates that micro switches used in the appliance must be approved to BS3955. Saia Burgess offer several miniature switches which are so approved by the BEAB component approval service. In most other countries there is similar concern that appliances operated in the home by unskilled people are as safe as human ingenuity can make them, and the use of approved switches is strongly indicated as a general rule.

Motor Control- Certain approval authorities, notably BEAB, CSA and U.L., apply horse power rating up to 2 HP to certain Saia Burgess switches. The tests carried out to establish these ratings are to specifications which may or may not have close relevance to the practical requirements of your application however, so Saia Burgess welcome the opportunity to examine all motor control circuits individually. Sometimes this involves a full laboratory test using a motor +which you will be asked to supply so that we are sure of obtaining the right conditions. Care should be exercised when using two single-pole switches or one double-pole switch to reverse a small motor - see right and wrong diagrams below. When wired the wrong way the supply can be short circuited if one moving contact is prevented from changing over when the other does, as could happen if the contacts welded temporarily or a two-switch installation lost alignment. A similar changeover time lag in a correctly wired system can only short circuit the load, still a fault condition but a safe one which will cause no damage.

Position Indication- As the actuating medium is moving in a straight line, a plunger actuated switch may be used. Small switching movements and a high level of repeat accuracy are necessary. Avoid exceeding the available over-travel, if necessary by providing a mechanical stop.

Printed Circuit Boards- Switches with tag terminals specially designed for printed circuit boards are to be found in both the ultra miniature and sub-miniature Saia Burgess ranges. The terminals on all these switches are suitable for flow soldering techniques.

Push Button Switching- A large selection of plain and lighted push button switching units are available. Most Saia Burgess plunger actuated switches may be used as switching elements behind push button arrays provided by the user.

Reciprocating Machinery- A micro or limit switch with adjustable lever will facilitate installation. The roller should be free when not engaged with the cam, and the faces of the cam should be shaped to depress and release the roller quickly but not abruptly. Relays- Micro switches with low force and movement differential characteristics are usually the most suitable for use as switching elements on relays. Consider the ultra and sub-miniature models..

Resistive Loads- Normally these offer the best conditions conducive to long switch life, but some care must be exercised if a thermostat, which holds the switch near its operating position, is included in the circuit or the load is a heating element capable of emitting red heat and thus behaving like a lamp with a high inrush current.

Safety in Industry- There are situations in all branches of industry where the safety of the operator or maintenance engineer depends to a major extent upon the correct functioning of a switch. The Saia Burgess Positive Action switches have been designed specifically to meet this need. All switches, of course, have finite life and even Positive Action switches will cease eventually to function correctly. Their design and construction is such that switch malfunction will not create danger; the safety application will ‘fail safe'. The complete security offered by Positive Action switches is not necessary in the majority of applications, when other switching characteristics or attributes may be judged to be the deciding factors in switch selection. Nevertheless it is reassuring to know that Saia Burgess snap-action switches are also safe and reliable when installed as recommended and used in the conditions for which they are designed.

Thermostats- Micro switches operated by thermostats are subjected to slow actuation, small movements in either direction which keep the contacts near to operating position for long periods, and frequent operation as the devices hunt around the specified temperature. Switches best suited to these exacting conditions are those with small movement differentials, which can build up adequate contact force quickly on either side of operation position Thermostat or Pressure-sensitive Devices- These difficult applications, involving very small and very slow actuating movements, demand a precision micro switch with tightly tolerance characteristics and a high value of repeat accuracy. Timing- A typical example of cam actuation. When a low torque motor is used on a multi-cam application it is important to use switches with small actuating forces, and thus miniature switches as are advocated.

Vibration- Spurious operation can be caused by vibration if this is sufficient to upset the normal working balance of the switch. As with the acceleration hazard, much can be done to reduce the effects of vibration by selecting switches requiring strong actuation force, and by mounting them so that the line of vibration is at right angles to the plunger travel.


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Section updated Apr 22, 2014
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