Quantcast Figure 3-13.Measuring circuit resistance with an ohmmeter.

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Custom Search
 
  
 
3-19 After you have adjusted the ohmmeter for zero reading, it is ready to be connected to a circuit to measure resistance. A typical circuit and ohmmeter arrangement is shown in figure 3-13. You must ensure that the power switch of the circuit to be measured is in the de-energized (OFF) position. This prevents the source voltage of the circuit from being applied to the meter, a condition that could cause severe damage to the meter movement. Figure 3-13.—Measuring circuit resistance with an ohmmeter. Remember that the ohmmeter is an open circuit when the test leads are separated. To take a resistance reading with a meter, you must provide a path for current flow produced by the meter’s battery. In view A of figure 3-13, the meter is connected at points A and B to produce this path. Connecting these test leads places resistors R1 and R2 in series with the resistance of the meter coil, the zero-adjust potentiometer, and the series multiplying resistor. Since you previously calibrated the meter, the amount of coil movement now depends only on the resistances of R1 and R2. The addition of R1 and R2 into the meter circuit raises the total series resistance and decreases the current. This decreases the amount of pointer deflection. The pointer comes to rest at a scale reading that indicates the combined resistance of R1 and R2. If you were to replace either R1 or R2, or both, with a resistor having a larger ohmic value, the current flow in the moving coil of the meter would be decreased even more. This would further decrease the pointer deflection, and the scale indication would read a still higher circuit resistance. View B is a simplified version of the circuitry in view A. From our ohmmeter discussion, two facts should be apparent: (1) Movement of the moving coil is proportional to the amount of current flow, and (2) the scale reading of the ohmmeter is inversely proportional to current flow in the moving coil. The amount of circuit resistance to be measured may vary over a wide range. In some cases, it may only be a few ohms; in other cases, it may be as great as 1 megohm. Scale multiplication features are built into most ohmmeters so that they will indicate any ohmic value being measured and offer the least amount of error. Most ohmmeters are equipped with a selector switch for selecting the multiplication scale desired. For example, view A of figure 3-14 shows a typical meter that has a six-position switch. The positions are marked on the meter in multiples of 10, from R 1 through R 100K.


Electrical News
Infographic: A History of Wearable Tech
Take a stroll down wearable memory lane in this great...
blog.designersofthings.com
18 Views of the Silicon Horizon
Semiconductors are poised for high single-digit growth this year and...
eetimes.com
Power Week: Did We Just Avoid an 'Electric Armageddon?'
While a powerful solar storm this past week resulted only...
eetimes.com
Rube Goldberg Rocket Launch
For their first real-world project, a group of budding young...
eetimes.com
Makers, Engineers Mix at NY Event
Educators and engineers from across the country attended New York's...
eetimes.com
Interview with Rod Elliott from Elliott Sound Products
Meet Rod Elliott the man behind the famous sound.westhost.com audio...
eevblog.com
Boeing, SpaceX Take US Back to Space Station
NASA taps Boeing Co., the safe but expensive choice, and...
eetimes.com
Technology You Can Sink Your Teeth Into
Thanks to 3D imaging software and a special milling machine,...
eetimes.com
Does Reducing Power Consumption Actually Save Energy?
It's the law of unintended consequences again, as regulations to...
eetimes.com
Local Motors Succeeds in Test Driving First 3D-Printed Car
3D-printed car has successful test drive!...
eetimes.com
Designer of Things Keynote Speaker: Gadi Amit
EETimes is pleased to announce that Gadi Amit will be...
eetimes.com
Sensor Hubs Aided by IEEE-2700-2014 Datasheets
The first MEMS standard, the IEEE 2700-2014, will standardize data...
eetimes.com
Dr. Duino Diagnostic Shield Deduces Dilemmas in Arduino Shield Stacks
When sandwiched an Arduino Uno and a shield -- or...
eetimes.com
Asia-Pacific IC Usage Domination Growing
Asia-Pacific is the dominant market for ICs for most products...
eetimes.com
Open-Source Hardware Circa 1920
An engineer discovers amazing schematics and documentation pasted to the...
eetimes.com
Intel Core M vs. Pentium M
A comparison of the Intel's recent Core M to its...
eetimes.com
WENS 540 Handheld 10MHz Oscilloscope and Debug Meter
A very brief look at the new WENS 540 Debug...
eevblog.com
Consumers Expect Full In-Car Connectivity
Drivers worldwide increasingly expect their cars to be "the next...
eetimes.com
iPhone 6 Future Revealed
Apple's new bigger iPhone 6 and 6 Plus are not...
eetimes.com
Lemoptix Pico-Projector Excels
Lemoptix is licensing its pico-projector technology to companies like Hamamatsu...
eetimes.com
 


Privacy Statement - Copyright Information. - Contact Us

comments powered by Disqus

Integrated Publishing, Inc.
9438 US Hwy 19N #311 Port Richey, FL 34668

Phone For Parts Inquiries: (727) 755-3260
Google +