Roland Barth • SCHURTER AG Whether you’re lighting up a swimming pool, sprinkling music, or making whirlpool bubbles, you need a switch for these functions.All of these applications are characterized by proximity to moisture.There are several switching technologies capable of managing this type of use.Before discussing these candidate devices, it may be helpful to briefly review the criteria that typically function in applications that may be exposed to moisture.
Switches designed for wet environments typically have an IP67 rating.This label refers to the IP code or ingress protection code.IP ratings classify and rate the degree of protection provided by mechanical and electrical enclosures, not only against water, but also against intrusion, dust and accidental exposure.It is published by the International Electrotechnical Commission (IEC).There is an equivalent European standard EN 60529.
The point of IP standards is to provide users with more detailed information about performance than what vague marketing terms like “waterproof” suggest.Each IP code can have up to four digits.They indicate compliance with certain conditions.The first number indicates protection against solid particles; the second indicates protection against liquid ingress.There may also be one or two additional numbers to indicate other protections.But the vast majority of IP ratings are in the single or double digits.
For general purpose and near wet applications, the most widely used technology is a mechanical switch with travel.We encounter them every day, like we turn the lights in a room on or off.They feature a wide range of actuation pressure points, high reliability and a wide range of products.
For mechanical switches for outdoor use, an IP67 rating is required.The reason is simple: mechanical switches that work according to the stroke principle have moving parts.Water can seep into the spaces between moving parts.In the presence of an ice point, ice on the actuator prevents the contacts from closing.The same applies to dirt, dust, steam and even spilled liquids.
In the case of keyboards and other user interfaces, membrane switches can be used when moisture is an issue.These are special mechanical switches made of silicone rubber and conductive carbon pellets or non-conductive rubber actuators.Through a compression molding process, an angled mesh is formed around the keyboard that collapses every time the user presses a key, creating conductive contact between the inner layers of the keyboard material.The outer layer of the keyboard is a continuous piece that can be sealed to prevent moisture from entering the layer that implements the mechanical switches.
But all in all, a mechanical switch that lacks an IP67 rating isn’t particularly suitable for wet areas.
Capacitive switches are currently experiencing rapid growth, in part due to their use in smartphones.No stroke, no moving parts.Capacitive touchscreen panels consist of an insulator, such as glass, coated with a transparent conductor, usually indium tin oxide (ITO) or silver.Because the human body is also an electrical conductor, touching the surface of the screen with a finger distorts the screen’s electrostatic field, which can be measured as a change in capacitance.Different techniques can be used to determine the location of the touch.
But capacitive touch switches are not the first choice for all applications.Some capacitive touchscreens cannot be used to detect fingers through electrically insulating materials such as gloves.For example, high air humidity or water droplets can also interfere with the touchscreen electrostatic field.Therefore capacitive switches are generally not suitable for use near swimming pools or whirlpools.
Piezo-based switches generate an electric charge under pressure.The compressive pressure of the finger push causes the (usually disc-shaped) piezoelectric element to bend slightly like a drumhead.Piezo switches produce a single, brief “on” pulse, typically used to turn on semiconductors, such as field effect transistors (FETs).In contrast to mechanical switches, piezoelectric switches have no moving parts.It can be sealed and IP rated up to IP69K.This feature predestines it to be used in the most adverse conditions.
Switches based on the piezoelectric principle are particularly robust.Piezoelectric elements (usually ceramics containing lead zirconate titanate or PZT, barium titanate or lead titanate) generate an electrical charge under pressure.The compressive pressure of the finger push causes the (usually disc-shaped) piezoelectric element to bend slightly like a drumhead.
Thus, the piezoelectric switch produces a single, brief “on” pulse that varies with the amount of pressure applied.This pulse is typically used to turn on semiconductors, such as field effect transistors (FETs).After the voltage pulse dissipates, the FET turns off.Capacitors can be used to store the resulting charge to increase the time constant of the gate and prolong the resulting pulse.
In contrast to mechanical switches, piezoelectric switches have no moving parts.It can be sealed and IP rated up to IP69K.This feature predestines it to be used in the most adverse conditions.
This brings us to pneumatic switches.For decades, these switches have been the go-to for pool and spa builders because they don’t handle electricity.They usually consist of a spring-loaded plunger that opens or closes the air passage when the operator presses a button.One disadvantage of pneumatic buttons is that their internal mechanics must be relatively precise, which is reflected in the price.
Like mechanical switches, pneumatic switches have moving parts that eventually wear out.Since they handle compressed air, pneumatic switches require special attention to sealing.It should also be mentioned here that these types of switches do not use optical feedback through point or ring lighting.
A growing number of pool and spa designers have recognized the benefits of piezoelectric switches.These devices are relatively inexpensive and very durable.They can handle aggressive chemicals often used in wet areas.Deutsche Welle
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