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Ohmmeter
An analog ohmmeter An ohmmeter is an electrical instrument that measures electrical resistance (the opposition offered by a circuit or component to the flow of electric current). Multimeters also function as ohmmeters when in resistance-measuring mode. An ohmmeter applies current to the circuit or component whose resistance is to be measured. It then measures the resulting voltage and calculates the resistance using Ohm’s law V=IR. An ohmmeter should not be connected to a circuit or component that is carrying a current or is connected to a power source. Power should be disconnected before connecting the ohmmeter. Ohmmeters can be either connected in series or parallel based on requirements (whether resistance being measured is part of circuit or is a shunt resistance.) Micro-ohmmeters (microhmmeter or micro ohmmeter) make measurements of low resistance. Megohmmeters (also a trademarked device Megger) measure large values of resistance. The unit of measurement for resist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ohmmeter
An analog ohmmeter An ohmmeter is an electrical instrument that measures electrical resistance (the opposition offered by a circuit or component to the flow of electric current). Multimeters also function as ohmmeters when in resistance-measuring mode. An ohmmeter applies current to the circuit or component whose resistance is to be measured. It then measures the resulting voltage and calculates the resistance using Ohm’s law V=IR. An ohmmeter should not be connected to a circuit or component that is carrying a current or is connected to a power source. Power should be disconnected before connecting the ohmmeter. Ohmmeters can be either connected in series or parallel based on requirements (whether resistance being measured is part of circuit or is a shunt resistance.) Micro-ohmmeters (microhmmeter or micro ohmmeter) make measurements of low resistance. Megohmmeters (also a trademarked device Megger) measure large values of resistance. The unit of measurement for resist ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Resistance And Conductance
The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with mechanical friction. The SI unit of electrical resistance is the ohm (), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ). The resistance of an object depends in large part on the material it is made of. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance. This relationship is quantified by resistivity or conductivity. The nature of a material is not the only factor in resistance and conductance, however; it also depends on the size and shape of an object because these properties are extensive rather than inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronic Test Equipment
Electronic test equipment is used to create signals and capture responses from electronic devices under test (DUTs). In this way, the proper operation of the DUT can be proven or faults in the device can be traced. Use of electronic test equipment is essential to any serious work on electronics systems. Practical electronics engineering and assembly requires the use of many different kinds of electronic test equipment ranging from the very simple and inexpensive (such as a test light consisting of just a light bulb and a test lead) to extremely complex and sophisticated such as automatic test equipment (ATE). ATE often includes many of these instruments in real and simulated forms. Generally, more advanced test gear is necessary when developing circuits and systems than is needed when doing production testing or when troubleshooting existing production units in the field. Types of test equipment Basic equipment The following items are used for basic measurement of voltages, cu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Resistance
The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with mechanical friction. The SI unit of electrical resistance is the ohm (), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ). The resistance of an object depends in large part on the material it is made of. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance. This relationship is quantified by resistivity or conductivity. The nature of a material is not the only factor in resistance and conductance, however; it also depends on the size and shape of an object because these properties are extensive rather than intens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Measuring Instrument
A measuring instrument is a device to measure a physical quantity. In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item under study and the referenced unit of measurement. Measuring instruments, and formal test methods which define the instrument's use, are the means by which these relations of numbers are obtained. All measuring instruments are subject to varying degrees of instrument error and measurement uncertainty. These instruments may range from simple objects such as rulers and stopwatches to electron microscopes and particle accelerators. Virtual instrumentation is widely used in the development of modern measuring instruments. Time In the past, a common time measuring instrument was the sundial. Today, the usual measuring instrum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Multimeter
A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped with voltmeter, ammeter, and ohmmeter functionality, or volt-ohmmeter for short. Some feature the measurement of additional properties such as temperature and capacitance. Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters (DMM, DVOM) have numeric displays and have made analog multimeters virtually obsolete as they are cheaper, more precise, and more physically robust than analog multimeters. Multimeters vary in size, features, and price. They can be portable handheld devices or highly-precise bench instruments. Cheap multimeters can cost under , while laboratory-grade models with certified calibration can cost over . History The first moving-pointer current-detecting device was the g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Safety Engineering
Safety engineering is an engineering discipline which assures that engineered systems provide acceptable levels of safety. It is strongly related to industrial engineering/systems engineering, and the subset system safety engineering. Safety engineering assures that a life-critical system behaves as needed, even when components fail. Analysis techniques Analysis techniques can be split into two categories: qualitative and quantitative methods. Both approaches share the goal of finding causal dependencies between a hazard on system level and failures of individual components. Qualitative approaches focus on the question "What must go wrong, such that a system hazard may occur?", while quantitative methods aim at providing estimations about probabilities, rates and/or severity of consequences. The complexity of the technical systems such as Improvements of Design and Materials, Planned Inspections, Fool-proof design, and Backup Redundancy decreases risk and increases the cost. T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Safety
Electrical safety testing is essential to make sure electrical products and electrical installations are safe. To meet this goal, governments and various technical bodies have developed electrical safety standards. All countries have their own electrical safety standards that must be complied with. To meet to these standards, electrical products and electrical installations must pass electrical safety tests. Some types of electrical safety tests include: *dielectric withstand test (also called a hipot test) *insulation resistance test (IR test) *earth continuity test *leakage current test Electrical safety tests are described in IEC 60335, IEC 61010, AS/NZS 3000, NFPA 70, BS 7671, and other national and international standards.\ Electrical Safety tests Dielectric voltage withstand test A dielectric voltage withstand test (also known as a hipot test) is done by applying a voltage higher than operating voltage to the device or installation under test. In this test, the el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Meters
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwell's equations. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others. The presence of an electric charge, which can be either positive or negative, produces an electric field. The movement of electric charges is an electric current and produces a magnetic field. When a charge is placed in a location with a non-zero electric field, a force will act on it. The magnitude of this force is given by Coulomb's law. If the charge moves, the electric field would be doing work on the electric charge. Thus we can speak of electric potential at a certain point in space, which is equal to the work done by an external agent in carrying a unit of positiv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kelvin Bridge
A Kelvin bridge, also called a Kelvin double bridge and in some countries a Thomson bridge, is a measuring instrument used to measure unknown electrical resistors below 1 ohm. It is specifically designed to measure resistors that are constructed as four terminal resistors. Background Resistors above about 1 ohm in value can be measured using a variety of techniques, such as an ohmmeter or by using a Wheatstone bridge. In such resistors, the resistance of the connecting wires or terminals is negligible compared to the resistance value. For resistors of less than an ohm, the resistance of the connecting wires or terminals becomes significant, and conventional measurement techniques will include them in the result. To overcome the problems of these undesirable resistances (known as 'parasitic resistance'), very low value resistors and particularly precision resistors and high current ammeter shunts are constructed as four terminal resistors. These resistances have a pair of cu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William Thomson, 1st Baron Kelvin
William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy at the University of Glasgow for 53 years, he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging discipline of physics in its contemporary form. He received the Royal Society's Copley Medal in 1883, was its president 1890–1895, and in 1892 was the first British scientist to be elevated to the House of Lords. Absolute temperatures are stated in units of kelvin in his honour. While the existence of a coldest possible temperature ( absolute zero) was known prior to his work, Kelvin is known for determining its correct value as approximately −273.15 degrees Celsius or −459.67 degrees Fahrenheit. The Joule–Thomson effect is also named in his honour. He worked closely with mathematics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Four-terminal Sensing
Four-terminal sensing (4T sensing), 4-wire sensing, or 4-point probes method is an electrical impedance measuring technique that uses separate pairs of current-carrying and voltage-sensing electrodes to make more accurate measurements than the simpler and more usual two-terminal (2T) sensing. Four-terminal sensing is used in some ohmmeters and impedance analyzers, and in wiring for strain gauges and resistance thermometers. Four-point probes are also used to measure sheet resistance of thin films (particularly semiconductor thin films). Separation of current and voltage electrodes eliminates the lead and contact resistance from the measurement. This is an advantage for precise measurement of low resistance values. For example, an LCR bridge instruction manual recommends the four-terminal technique for accurate measurement of resistance below 100 ohms.Manual for the Racal-Dana Databridge 9343M: "If the resistance value is low, less than 100 ohms, make a four-terminal connection. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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