n.
An instrument for direct measurement in ohms of the resistance of a conductor in ohms.
ohmmeter
Dictionary:
ohm·me·ter (ōm'mē'tər)  |
| 5min Related Video: ohmmeter |
| Sci-Tech Encyclopedia: Ohmmeter |
A portable instrument for measuring relatively low values of electrical resistance. The range of resistance measured is typically from 0.1 microhm to 1999 ohms (Ω).
The ohmmeter solves quickly and easily a variety of measurement problems, including measuring the resistance of cladding and tracks on printed circuit boards, electrical connectors, and switch and relay contacts, as well as determining the quality of ground-conductor continuity and bonding, cables, bus-bar joints, and welded connector tags. See also
| Columbia Encyclopedia: ohmmeter |
ohmmeter (ōm'mē'tər), instrument used to measure the electrical resistance of a conductor. It is usually included in a single package with a voltmeter, and often an ammeter. In normal usage, the ohmmeter operates by using the voltmeter to measure a voltage drop, then converting this reading into a corresponding resistance reading through Ohm's law. If the current is known, the voltage drop across the unknown resistance may be read to give the resistance directly. If the current is not known, or if it is not possible to measure the voltage across the unknown directly, reading the voltage drop across a known resistance in the same circuit will give the current, and once this voltage is subtracted from the total drop for the circuit, the voltage drop across the unknown, and thus its resistance, may be found.
| Veterinary Dictionary: ohmmeter |
An instrument that measures electrical resistance in ohms.
| Electronics Dictionary: ohmmeter |
| Wikipedia: Ohmmeter |
An ohmmeter is an electrical instrument that measures electrical resistance, the opposition to an electric current. Micro-ohmmeters (microhmmeter or microohmmeter) make low resistance measurements. Megohmmeters (aka megaohmmeter or in the case of a trademarked device Megger) measure large values of resistance. The unit of measurement for resistance is ohms (Ω).
The original design of an ohmmeter provided a small battery to apply a voltage to a resistance. It used a galvanometer to measure the electric current through the resistance. The scale of the galvanometer was marked in ohms, because the fixed voltage from the battery assured that as resistance decreased, the current through the meter would increase.
A more accurate type of ohmmeter has an electronic circuit that passes a constant current (I) through the resistance, and another circuit that measures the voltage (V) across the resistance. According to the following equation, derived from Ohm's Law, the value of the resistance (R) is given by:
For high-precision measurements the above types of meter are inadequate. This is because the meter's reading is the sum of the resistance of the measuring leads, the contact resistances and the resistance being measured. To reduce this effect, a precision ohmmeter has four terminals, called Kelvin contacts. Two terminals carry the current from the meter, while the other two allow the meter to measure the voltage across the resistor. With this type of meter, any current drop due to the resistance of the first pair of leads and their contact resistances is ignored by the meter. This four terminal measurement technique is called Kelvin sensing, after William Thomson, Lord Kelvin, who invented the Kelvin bridge in 1861 to measure very low resistances. The Four-terminal sensing method can also be utilized to conduct accurate measurements of low resistances.
See also
 |
Wikimedia Commons has media related to: Ohmmeters |
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Learn More
 | teraohmmeter (engineering) |
| insulation testing set (engineering) |
| ammeter (measure, instrument – in electricity) |
 | How do you connect an ohmmeter in a circuit? Read answer... |
| What is a good 30 amp fuses reading using a volt-ohmmeter? Read answer... |
| Why must an analog ohmmeter must be adjusted? Read answer... |
Help us answer these
 | Who invented the ohmmeter? |
| An ohmmeter can be damaged if? |
| How does an ohmmeter works? |
Post a question - any question - to the WikiAnswers community:
Copyrights:
 |
 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
 |
| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
 |
| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
 |
| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
 |
| Electronics Dictionary. Copyright 2001 by Twysted Pair. All rights reserved. Read more |
 |
| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Ohmmeter". Read more |
Related answers
- What is an example of Ohmmeter?
- Most ohmmeters have a?
- Uses of ohmmeter?
- How can an ohmmeter be damaged?
- How do you take care of an ohmmeter?
ADVERTISEMENT
Answer these
- Why is ohmmeter called an ohmmeter?
- Where you can apply ohmmeter?
- What uses of ohmmeter?
- How the ohmmeter worked?
- How an ohmmeter works?
Mentioned in
- teraohmmeter (engineering)
- insulation testing set (engineering)
- ammeter (measure, instrument – in electricity)
- voltmeter (instrument – in electricity)
- Shunting
- Multimeter
- Circuit testing (electrical engineering)
- Electrical measurements (electricity and magnetism)
- Power-off testing
- Micramperimeter
- Kelvin bridge
- Fluke Corporation
- Electronic instrumentation
- Microwave solid-state devices (physical electronics)
