What is contact bounce and how it so bad

Today I want to tell you about the phenomenon as contact bounce, as well as that with the help of some try to minimize the actions and completely neutralize the effect of this is highly undesirable phenomenon.

Table of contents

What is contact bounce

Causes of bounce

What is so bad "rattle"

How to eliminate and suppress ringing

conclusion

What is contact bounce

So, first let's find out what kind of contact bounce phenomenon. All electromechanical devices that are designed for switching, there is at least one contact pair with which just happens closing and opening electrical components.

The main drawback of electromechanical contacts is arbitrary re-switching after activation of the contact pair, due to the elasticity of the contact system as a whole.

It is this phenomenon and came to be called - contact bounce and struggle with him almost from the beginning, as soon as there were elements of automated systems.

Causes of bounce

When two elastic bodies interact (under the action of clamping force), is their slight deformation. In this case, the elastic force tends to compensate for the distorting effect, with the result that the elastic body prepared return pulse and repel each other (but again pushes downforce Plates). Subsequent repulsion occurs with decaying amplitude until it has completely stopped.

Let's do an experiment to demonstrate this effect: Take a small metal ball and throw it to the low height of the metal plate. So that the ball striking the plate will jump back up, and then again hit the plate and bounce back. This will continue until the ball is not completely freeze on the plate.

This very simple experiment demonstrates that a contact bounce.

In contact rigid contacts as there is a series of vibrations that trigger a chain of open circuit. The result of these interruptions is a series of pulses which can be illustrated as follows:

The figure above shows that the ideal operation expressed single rectangular pulse. The actual operation of the picture below, is as far from reality as the additional noise introduced arcing contacts.

Moreover, the number of touches of contacts depends on:

1. Properties of the switching node components.

2. The voltage on the windings of the relays.

3. The elastic contacts and some other factors.

The problem of bounce is observed by opening the switching group, but to a much lesser extent.

What is so bad "rattle"

In order to understand what bad rattle, you need to consider the processes taking place during this operation.

So, as soon as the contacts are separated from each other at a distance sufficient for the ignition of the arc, between they arc begins to burn and the more powerful switching power, the greater the devastating effect it provides.

For example, in conventional light switches contact bounce is simply ignored. But the scheme of a variety of electronic devices painfully suffer frequent switching currents.

Almost all digital electronics sees bounce like a whole series of signals. These false code may well lead to malfunctions and even damage sensitive electronics.

How to eliminate and suppress ringing

Without making design changes in a contact group to neutralize bounce is simply unrealistic. An example of successful modernization, after which almost completely eliminated the problem of chatter are P2K button or a slide type switches.

But there are other ways to debounce, namely:

The hardware method

To reduce the wear of the switching in various relays are often used:

1. Shunt RC - chains.

2. Varistors.

3. Wheeling diodes.

4. Zener diodes.

5. Circuits which use a combination of several devices.

These chains can reduce jitter by smoothing of abrupt current characteristics. These chains are mounted parallel to the load or to the contact group.

Each scheme has its drawbacks like, as well as a clear advantage.

Using triggers

Just an excellent job with debounced so-called triggers - Specialized electronic circuit.

These schemes are transformed with the analog signal to digital as well as operate the inversion of logic levels.

In such products is taken into account only part of the signal, whose time exceeds the setting value. Switching triggered reporting is performed when the upward or downward signal exceeds the upper or lower threshold.

The use of reed switches

Reed especially in those where the contact group is wetted with mercury, making them ideal for low power switching circuits. Due to its structural features in the reed switches with mercury is almost no effect of bounce.

The software method of elimination

In order to neutralize the effect of chatter in various electronic devices used special software processing the incoming signal. This method is fairly robust and has only a insignificant drawback - the signal delay time may reach (depending on the processing algorithm) to 0.1 seconds.

Software processing allows to obtain the perfect boost that ensures a stable and reliable operation of most digital devices.

conclusion

Of course, the problem of contact bounce is present, and the methods used by the suppression of this effect are quite reliable and are suitable for most modern circuits.

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