Sealed Micro Switch Likes it Humid

Switching electrical power or signals has been a basic function for decades. One of the devices that perform this operation is a snap action based switch, manufactured in very large quantities by multiple manufacturers. The largest market segment in power switching ( up to 15 Amps ) is for applications with simple requirements, mostly in appliance related applications. A simple micro switch without any specific protection against water, dust or temperature will do the job.

But for industrial applications the requirements become much more challenging. Water and dust proofing become an important consideration. All of a sudden an operating temperature range of – 10°C to 80°C is not sufficient anymore. Switches may be mounted on a machine which heats up when operating and therefore an operating temperature of 100 120° C may be a needed requirement. Also, it is not uncommon having industrial equipment working outside where temperatures may drop to 40° C and the equipment is still required to operate properly.
Guaranteeing a high degree of sealing, while operating under a wide temperature range, demands very good choices in material and switch design. To achieve a sealing against water or oil a flexible membrane has to seal the space between the moving pin and the housing. Several possibilities exist to hold the seal in place; the technique used determines the quality of the sealing and the applicable temperature. The selection of the rubber material is important as the membrane has to keep its flexibility over the entire operating temperature range. It should not crack or become too hard at low temperatures.

To guarantee a tight seal, Microprecision uses a pin made out of two parts. The membrane is squeezed between the parts and held securely in place. It’s attached to the housing using a plastic ring, which compresses the membrane to the housing and held in place through ultrasonic welding. This approach guarantees a tight fit of the seal even when wide temperature fluctuations are impacting the flexibility of the rubber membrane, or when an outside pressure change is pressing on the membrane.