To clarify how the occurrence of contact welding is related to the series of arc duration characteristics in consecutive make and break operations, electrical endurance tests were conducted on commercially available automotive relays, and the voltage waveforms of make and break arcs between the electrodes were recorded with LabVIEW. Experimental results indicate that welding may occur suddenly or randomly with increasing number of operations. A single arc or a group of make or break arcs with a long arc duration does not necessarily result in contact welding, but a group of longer make or break arcs within a narrow range of operation numbers can cause imminent contact welding (such an effect can be called the “group of longer arcing duration effect”). It is confirmed that contact welding may occur in both make and break operations, but the welding probability during make operations is much higher than that during break operations.

A new scheme for evaluation of shapes of pips and craters formed by arc discharges on electrical contact surfaces is proposed. Measuring a height of a pip or a depth of a crater as well as an average diameter thereof with a scanning laser microscope and then putting a plot having the measured values as its vertical and horizontal coordinates enable us to numerically and briefly evaluate shapes of those pips and craters on arc-damaged contact surfaces. Some exemplary results obtained by this evaluation scheme are presented here.

Some experimental results on the contact phenomena that have been observed with electrical contacts operated to break an inductive DC load current in nitrogen atmosphere and in air (laboratory atmosphere) are presented. When Ag, Pd and Cu contacts were operated to break an inductive DC load current in the range of 1.0 A to 3.0 A in nitrogen atmosphere, more stable contact resistance characteristics were obtained, as compared to the case where operated in air, or at least the occurrence of unstableness and increase in contact resistance was delayed. The arc duration in nitrogen atmosphere became shorter in general than in air, especially with the Pd and Cu contacts. Voltage waveforms of arc discharges in the Ag and Pd contacts operated in nitrogen atmosphere showed a relatively clear step-like transition from the metallic phase to the gaseous phase as compared to the case where operated in air, while the Cu arcs did not show such significant differences due to the surrounding atmosphere. Although any apparent differences on the contact surface conditions in connection with the surrounding atmosphere were not clearly observed after the switching operations, the anode mass change characteristics were found to be more significantly affected by the difference of surrounding atmospheres than the cathode mass changes. The obtained experimental results suggest that the difference in the surrounding atmosphere introduce some difference in the anode surface morphology, possibly through the deposition of arc products in different deposition patterns, which will then result in differences in the contact resistance characteristics.

This letter presents the results of Auger analysis of surface products by steady arc on Ag/Pd contacts. Black products formed on Ag contact surfaces, which make contact resistance high and unstable, are silver oxide. In the case of Pd contacts, contact resistance of which remains low and stable, white-colored products seen after operations seem to be powdery palladium.

In this letter the formation of palladium-oxides on AgPd 70 and AgPd50 contacts caused by mechanical switching actions is reported. Further, palladium-oxides are found to show non-linearity of contact resistance when contact potential drop gets over about 0.3 V.

In this letter, it is confirmed that contact resistance of AgPd70 contacts through mechanical break-make operations remains low despite of palladium-oxides formed on the electrode surfaces. Also, material transfer due to the difference of hardness is found to influence the formation of the products.

Arc discharge between electrodes of relays and switches often causes contact surface damage through material transfer and arc erosion. Especially, material transfer sometimes occurs and brings serious failure even under lower load that is quite smaller than the minimum arc current value of contact material. In this paper, contact surface configuration, material transfer, and arc erosion characteristics of Ag and AgPd 60 contacts were experimentally studied after 0.5 or 1 million switching operations at various load levels. The followings can be made clear. Firstly, it was confirmed that the arcs and material transfer occurred even under such current that was lower than the minimum arc current. Therefore, the definition of the arc occurrence boundary current was newly determined. Secondly, the relation between load conditions (current and power supply voltage) and contact surface configuration (craters and pips) caused by material transfer was studied. The arc erosion behaviors of tested samples could be classified into two types: material transfer type and wear-out type. As one of the primary factors of transition from the former type to the latter one, contact activation was considered. The influences of load conditions and organic gas emitted from relay structure on arc characteristics was experimentally examined. The results indicated that load current greatly influenced the amount of material transfer and that power supply voltage affected the occurrence of the wear-out type significantly. The activation behavior of the contact surface could be found through observing the bridge voltage waveform.

In order to study the influences of contact opening speeds on arc extinction gap length characteristics, Ag contacts were operated to break DC inductive load currents from 0.1 A to 2.0 A at 14 V with contact opening speeds of 0.5 mm/s, 1 mm/s, 2 mm/s, 5 mm/s and 10 mm/s in a switching mechanism employing a stepping motor, and arc voltage waveforms were observed at each opening of the contacts. From the results, the average arc durations were determined at each current level under the respective contact opening speeds, and the average arc extinction gap lengths were calculated by multiplying the average arc duration value and the contact opening speed value. It was found that average arc durations showed no significant differences with increasing contact opening speeds. Thus, arc extinction gaps became larger at faster opening speeds in the inductive load conditions of this study.

In March, 2007, IEEE802.15.4a was standardized as a low-rate and low-power UWB system for sensor networks. In general, detection of the IEEE802.15.4a signal is considered to be difficult because of its low transmitting power density and low duty cycle. However, if detecting of the IEEE802.15.4a signal is available, it is possible to avoid interference issues both among the IEEE802.15.4a systems and between the 15.4a and other UWB systems. This letter proposes a simple detection method using non-coherent detectors. The possibility of detecting of the IEEE802.15.4a signal by proposal detection method was examined. By conducting experiments with an emulated 15.4a RF signal, the signal detection probability was examined, and 15.4a signal from the range of about 11 meters in the radius could be detected. From this observation, the CSMA/CA method with detecting the signal in 15.4a system may be applied for alternative access method for 15.4a systems.

Arc occurrence rates were measured for Ag contacts in DC resistive and inductive load circuits. In inductive load conditions, arc occurrence rates in general came close to 100% at around 0.4 A, the conventional minimum arc current level of Ag. In resistive load conditions, the similar results were obtained with 30 V, while arc occurrence rates close to 50% were still obtained at around 0.4 A with 14 V and 10 V. Careful attention should be paid to the term "minimum arc current" to avoid misinterpretation thereof.

The authors have been interested in a Scanning Laser Microscope (SLM) and applied it to studies of contact phenomena. In particular, a digital SLM is being currently used, and confirmed to be a successful tool for investigating the contact phenomena. In this paper, the theory and mechanism of a digital SLM are briefly explained, and some actual data obtained with the digital SLM are presented for demonstrating its usefulness for studies of contact phenomena.

The dependence of arcing duration and energy in break operations for automotive relays was analysed with breaking current/voltage waveforms. Endurance tests were conducted with AgSnO2, AgNi10 and AgNi0.15 contacts under the loads of resistance, lamp and inductance, respectively, at 14 VDC. The experimental results shows breaking current (or break arc) duration is usually low and stable before welding occurs. The welding may appear suddenly or randomly without any preceding cumulated increases in the arc duration, the quantity of electric charges, nor the arcing energy. The welded contacts may be re-opened in the later break operation and, thereafter, can keep on working normally for many times.

In order to realize better understanding of influential order sequences of surrounding atmospheres on break arc durations of electrical contacts in DC load conditions, a quantitative mathematical model, which aims to indicate dependences of break arc durations on several gas parameters such as molecular mass, viscosity, specific heat capacity, thermal conductivity, electro-negativity, and ionization potential, was analyzed. Break arc durations of AgCdO contact pairs were measured in several kinds of surrounding atmospheres (N2, Ar, He, air, O2 and CO2) under different DC voltage and current conditions, and data fitting processes were conducted. As a result, a candidate mathematical model was established, which could indicate possible influential order sequences of surrounding atmospheres on break arc durations in the range of the tested conditions.

Application of transverse magnetic field (TMF) is one of the most important ways to improve electric life and breaking capacity of DC relays. For better understanding of dependence of arc durations on transverse magnetic field, a series of experiments were conducted under an external transverse magnetic field with 12 pairs of AgSnO2 contacts in a DC 28 V 60 A/30 A/5 A circuit, respectively. By using permanent magnets, the transverse magnetic field was obtained and the magnetic flux density at the gap center was varied from 13 to 94 mT. The results show that breaking arc duration is decreased monotonically with increases in the magnetic flux density, but making arc duration isn't decreased monotonically with increases in the magnetic flux density. In addition, both the magnetic flux density and the breaking arc duration have threshold values Bl and Tbmin, respectively, which means the breaking arc duration is almost stable with the value Tbmin even if the magnetic flux density is higher than Bl.

Topographical changes induced by optical near-field around photo-irradiated nanoparticles were attained using a pulsed laser with a large peak power as a light source. The arrayed structure of nanoparticles was transcribed on urethane-urea azo copolymer film as dent structure. The experiments by the pulsed laser of different wavelength showed that the topographical change was caused by the light absorption. The dent diameter and the dent depth changed depending on the diameter of nanoparticles.

Even in today's industries that are predominated by solid-state switching devices, electromechanical devices with electrical contacts are still widely used for switching and/or conveying electrical signals and power. In this paper, some interesting topics in the investigation of electrical contacts, which were selected mainly from those presented at recently held international conferences or submitted to the related Transactions of IEEE and IEICE, are introduced. Specifically, some topics related to investigation regarding contact materials, new techniques for evaluating electrical contact phenomena, new understanding of the contact phenomena, and new applications of electrical contacts are briefly explained.

When AgSnO2 contacts were operated to break an inductive DC load current of 14V-12A, 20V-7A or 20V-17A at a contact opening speed of 10mm/sec or slower, application of an external magnetic field resulted in reductions in break arc durations even without magnetic blowing. Simple estimation of Lorentz force to be applied onto arc column revealed that a certain minimum magnitude of Lorentz force seems to be required for initiating arc blowing. Certain relationships between the Lorentz force magnitude and the timing of metallic-to-gaseous phase transition were also found to exist.