In modern electrical control systems, electromagnetic relays are an extremely important basic device. Whether it is industrial automation, household appliance control, or smart grid equipment, most of its core switching functions are performed by relays. However, in the actual work of the relay, the contact bounce phenomenon becomes an important hidden danger that affects its reliability and service life.
Based on experimental research, the influence of various physical factors on contact bounce behaviour has been systematically explored, and a series of optimisation suggestions with practical significance have been put forward. In this paper, the research results will be summarised and interpreted to provide reliable reference for relay manufacturing and application engineering.
When the relay coil is energised, the moving iron core is rapidly attracted under the action of electromagnetic force, making the contacts close; when the power is cut off, they are released. However, in the process of contact closure or disconnection, due to mechanical inertia, spring force and unevenness of the contact surface, the contacts will repeatedly bounce between each other in a very short period of time - multiple contact and separation.
This phenomenon manifests itself in the waveform as a spike jitter in the electrical signal (usually lasting between 0.5 and 10 ms), which can cause false triggering or state uncertainty in the control logic.
Although the duration of each bounce is extremely short, in some applications that require high signal accuracy, such as PLC control, power management, motor drive, etc., this jitter may cause incorrect judgement or false action, which in turn leads to system instability.
The contact bounce problem can cause significant interference in the following scenarios:
High-speed data sampling or pulse signal control occasions (such as counters, PLC inputs)
High-frequency switching power supply, relay matrix circuits
Automated testing, industrial control systems
Applications requiring high load switching accuracy, such as power meters, charging piles
Voltage level: the higher the voltage, the greater the electromagnetic suction, the faster the contact suction speed, but the mechanical shock that comes with it is also more violent and prone to violent rebound.
Driving waveform: Trapezoidal waveform and PWM waveform can alleviate the suction shock and reduce the bounce amplitude to a certain extent compared with the traditional DC pulse.
Spring stiffness and rebound rate: the larger the spring stiffness, the faster the rebound, but not conducive to the stable closure of the contact; optimising the spring design is one of the core links to inhibit the bounce.
According to experimental research, moderately reducing the spring stiffness can significantly reduce the number of rebound and contact failure rate.
Although silver nickel, silver tin oxide and other materials have good electrical conductivity, they are prone to surface arc erosion under high-speed closure;
Roughness or geometric asymmetry of the contact surface (e.g., corner impact) is also an important factor in the generation of bouncing;
Surface plating detachment and oxidation will also trigger local unstable contact and increase the probability of bouncing.
The arc-like raised shape results in a faster contact apposition time and weaker bouncing phenomenon compared to planar collision structures.
When the mass of the moving iron core and the swing arm part connecting the contacts is larger, the accumulation of inertial potential energy is also larger.
Through the structure of lightweight design and the introduction of damping materials can effectively buffer the movement of the bounce fluctuations.
Relay life is usually divided into electrical life (affected by on-off current shocks) and mechanical life (affected by frequent movements and physical wear). Bouncing phenomenon will bring double threats:
Reduced electric life: repeated on-off process may cause multiple arcs, erosion of contacts and increase contact resistance;
Shortened mechanical life: high frequency impact causes spring fatigue, loose solder joints, affecting the overall stability of the relay.
False action rate increases: in the digital control system, if the control signal sampling period in the bounce window period, it is very easy to be judged as multiple triggering, which will lead to program abnormalities, frequent relay closure, load false triggering and other serious consequences.
Adopt low inertia and light mass dynamic contact design to reduce the kinetic energy of impact;
Increase mechanical cushioning or damping structure (e.g. rubber cushion, oil damping);
Optimise contact docking angle to improve contact area and fit;
Use curved or bevelled contacts to reduce the probability of bouncing.
Use of highly abrasion-resistant contact materials such as silver tin oxide, silver graphite, etc.;
Addition of gold-plated and nickel-plated treatments to improve oxidation and arc corrosion resistance;
Surface nano-coatings to reduce friction and improve electrical conductivity.
Add filter circuit or anti-jitter module
Set up ‘de-jitter delay’ logic in the programme, such as delayed sampling, double edge confirmation, etc.
Use voltage retarded start-up to slow down the speed of the suction
Use alternative solutions such as solid state relays (SSRs) or magnetically held relays to avoid frequent mechanical actions.
Although relay bounce is only a small problem at the micro level, it plays a decisive role in the stability and safety of the whole control system. The research of Xiong Jun et al. provides a theoretical basis and engineering improvement direction for the industry through experiments and data analysis, which has high practical value.
Enterprises should pay attention to the bounce parameters when selecting or designing relay products, and do customised optimisation in combination with the usage scenarios, in order to enhance the overall reliability and market competitiveness of the products.
