A quantitative observation of damage on the electrical contact surface is very difficult so far because of no proper measuring system. Therefore, developement of a new measuring system for this purpose is needed for performance estimation of characteristics of electrical contacts. A digital image signal processing technique was applied for this purpose and the experimental results show that the developed system is very useful for quantitative observation of contact surface.

Holographic pattern measuring system (HPMS) which has been developed by the authors as applied to measure a thermal deformation of contact spring due to current flow. As the results of investigations, a microscopical rolling of contact point was clarified and a relationship between the changing spring shape and the contact voltage was qualitatively mode clear.

Surface damage of the electrical contact is a primary cause of failure in many electronic devices which use sliding contacts. Therefore, the quantitative observation of the contact surface is one of the most important subjects for improvement of contact reliability. In this study, in order to clarify the relationship between the contact resistance and the damage on the contact surface, a digital image measuring system (DIMS) was developed. A shadow image processing technique (SIPT) was applied to the damage analysis on the sliding contact surface. The damage width on the contact surface and the damaged image could be obtained with a 3-D graphic image by applying both DIMS and SIPT. Part of the relationship between the damage on the contact surface and the contact resistance could be obtained in the case when Cu is used for the moving contact and Cu and Ni are used for the static contact.

In this paper, a Micro-Step-Separating System is realized for investigating phenomena of initial state of separating contacts. This system can control the contact separation in a discrete way with about 0.5 µm step. By using this system, we observed a relationship between contact voltage and contact separation gap. Ag contacts were observed. The observation showed that the contact voltage rose up and then fell down to the stable voltage at each step separation. From this observation, we expect to elucidate the contact bridge phenomena with more sophisticated way because we can approach them under the thermal equilibrium condition.

The authors developed new measuring system (Holographic Pattern Measuring System [HPMS]), which is composed of both techniques of holography and graphic image processing, was used to measure the vibrations of a printed circuit board (PCB) due to operation of a mounted electromagnetic relay on it. The clear vibration patterns were obtained. By using pattern analysis processor, quantitative vibration patterns of the PCB surface were observed. Both the vibration patterns and displacements were changed by edge fixing way of the PCB.

The mechanism of dark bridge formed with very slow contact separating speed was empirically shown with some discussions from the experimental results which the authors have obtained by using the cantilever system for controlling contact gap. By analyzing the obtained results, we will assume some concept of formation mechanism of dark bridge. Since the thermal effect is inevitable in the bridge formation, this will be inferred from two points; one is the a-spot change at initial state of bridge forming, and another one is the thermal expansion due to bridge current that affects the shape of bridge. This paper will show from these two points the conceptual bridge formation mechanism in case of non-melting state of contact bridge which is called here dark bridge.

From the authors' investigations on the initial instantaneous phenomena in breaking contacts, we have found the two types of bridge, i.e. one is a brightened (luminous) bridge and another one is a dark (non-luminous) one. This paper discusses on the dark bridge formed between contacts when the separation speed is very small. The following items are mentioned in this paper: a) bridge model and theory on the relationship between bridge length and diameter. b) thermal flow from bridge to its vicinity, c) deduction of a thermal equilibrium condition from the calculation of thermal flow time constant. d) experimental works, e) discussions and f) conclusions. In conclusion, we see the coincidence of the tendency of the theory and experiment carried out on the relationship between bridge diameter and length.

A holographic pattern measuring method which combines both techniques of holography and graphic image processing was developed. As a typical application, this method was applied for the analysis of thermal distortion of a printed circuit board (PCB) due to current flow through a point contact, and quantitative thermal distortion pattern of the PCB was obtained.