Measuring resistance with Ohmmeter

journal1

New article from the series of tutorial that Nasir – one of our most prolific members – wrote on measuring instruments. This time he focuses on ohmmeter.

You too can send us articles. Just send a mail to the team!

 

What is an Ohmmeter?

Ohmmeter is another interesting measuring instrument that is used for measuring the resistance between any two points in the circuit. It is of extreme importance and is widely used in circuit analysis and debugging nowadays.

As we know that the units of resistance are ohms, so we know that where the name of this device comes from, as it measures the ohms between any two points in the circuit.

How does an ohmmeter measure resistance?

For measuring the amount of resistance in the circuit, the first and foremost thing that needs to be checked is that the ohmmeter should have its own built in voltage supply. This can be in the form of a small battery, typically 1.5 volts used for normal everyday purposes, but different ratings are also available.

The need for a built in voltage supply arises from the fact that for measuring the resistance, the ohmmeter passes the current through that place and then measures the drop in voltage that is the resistance through the output value of the current.

For measuring the unknown resistance, the voltage supply of the circuit is first turned off and then the two probes of the ohmmeter are connected to the two points between which the value of resistance needs to be measured.

The red probe is connected to the positive side of the circuit and the black probe is connected to the ground side of the circuit, as shown below:

Measuring resistance with Ohmmeter 1
When the ohmmeter is turned on, the current from the battery passes through the circuit and the voltage drop or resistance i.e. the opposition to the electron flow is measured.

 

Types of ohmmeter

Ohmmeters are available in two forms i.e. the digital ohmmeter and the analogue ohmmeter. The digital ohmmeter displays the value of unknown resistance digitally, in the form of numeric digits. And the analogue ohmmeter displaces the value through a moving needed on a marked scale. When the current passing through the circuit is maximum with respect to the input voltage, the resistance is said to be minimum, according to ohms law.

Vice versa, when the current is minimum the resistance is maximum and the needle moves to the extreme left of the scale to indicate the maximum value of ohms, as shown in the figure below:

Measuring resistance with Ohmmeter 2
Ohmmeter can also be used to measure the variable resistance of a variable resistor.

 

Calibrating your Ohmmeter

In order to check if your measuring device is working correctly, just connect the two probes of the ohmmeter with each other.

This should show the minimum level of resistance, which is ideally zero and can practically be a few micro or milliohms.

 

Applications of ohmmeter

  1. These are being widely used now a days to check circuit continuity, i.e. if enough current is flowing through the circuit or there is infinite resistance between two points and the circuit id disconnected.
  2.  

  3. They are also used as laboratory testing equipment in different experiments and for teaching purposes.
  4. They are quite useful in debugging small chips like printed circuit boards and other stuff which needs to be implemented in sensitive equipment.

 

TOP 5 Best Sellers voltmeter on amazon

Sale 2019Bestseller No. 1
Klein Tools 69149 Electrical Test Kit with Multimeter, Non-Contact Voltage Tester and Receptacle...
238 Reviews
Klein Tools 69149 Electrical Test Kit with Multimeter, Non-Contact Voltage Tester and Receptacle...
  • The MM300 multimeter measures AC/DC voltage, DC current and resistance and has a safety rating of CAT III 600V, Class 2, Double insulation
  • The NCVT-1 has a bright green LED to indicate the tester is working; it changes to red and warning tones sound when voltage is detected
  • NCVT-1 has a digitally-controlled ON/OFF power button and auto power-off feature to conserve and extend battery life
  • Receptacle tester detects wiring configurations and indicates correct wiring, and identifies common wiring faults
  • Identifies open ground, open hot, open neutral, hot/ground reversed; it does not indicate quality of ground, multiple hot wires, or a combination of defects
Sale 2019Bestseller No. 2
Klein Tools CL110KIT Electrical Maintenance & Test Kit For AC/DC Voltage, Resistance & Continuity,...
93 Reviews
Klein Tools CL110KIT Electrical Maintenance & Test Kit For AC/DC Voltage, Resistance & Continuity,...
  • Measure AC current via the clamp, and AC/DC voltage, resistance and continuity via test leads
  • Detects the most common wiring problems in standard and GFCI receptacles including open ground, reverse polarity, open hot, open neutral and hot/ground reversed
  • Line splitter allows the measuring of current draw up to 15A without splitting the load's power cord
  • CAT III 600V, Class 2, Double insulation safety rating
  • AC Auto-Ranging 400 amp digital clamp meter
Sale 2019Bestseller No. 3
AstroAI Digital Multimeter, TRMS 6000 Counts Volt Meter Manual Auto Ranging; Measures Voltage...
579 Reviews
AstroAI Digital Multimeter, TRMS 6000 Counts Volt Meter Manual Auto Ranging; Measures Voltage...
  • WIDE RANGE of tests for Voltage, Current, Resistance, Continuity, Capacitance, Frequency; Tests Diodes Transistors, Temperature
  • PROFESSIONAL LEVEL features include Auto-Ranging capability, and True RMS for measuring both AC Current and Voltage
  • EASE OF USE: Convenient features like Data Hold, Large LCD Backlit Screen, Auto Shut-off and Hanging Magnet, and Kickstand make taking and recording measurements easier than ever before
  • IDEAL FOR COMMERCIAL settings where it can handle the demands of a long workday, from the durable exterior to the wide range of heavy-duty capabilities
  • Built-in F400mA/600V and F10A/600V explosion-proof ceramic fuse tubes; Double Protection, more secure and reliable; The fuses can protect the multimeter effectively; Overload protection on all ranges....
Sale 2019Bestseller No. 4
Fluke 117 Electricians True RMS Multimeter
624 Reviews
Fluke 117 Electricians True RMS Multimeter
  • VoltAlert technology for non-contact voltage detection
  • AutoVolt automatic AC/DC voltage selection. DC millivolts - Range : 600.0 mV, Resolution : 0.1 mV
  • Low input impedance: helps prevent false readings due to ghost voltage
  • Large white LED backlight to work in poorly lit areas
  • True RMS for accurate measurements on non-linear loads.Operating temperature:-10°C to +50°C.Battery life:400 hours typical, without backlight
Sale 2019Bestseller No. 5
Etekcity Auto Ranging TRMS 6000 Counts Digital Multimeter, AC/DC Amp Ohm Voltage Tester Meter with...
68 Reviews
Etekcity Auto Ranging TRMS 6000 Counts Digital Multimeter, AC/DC Amp Ohm Voltage Tester Meter with...
  • PROFESSIONAL CALIBER: with fully inclusive testing options, precise true RMS readings, and a voltage range up to 1000V, enjoy all the advanced capabilities The MSR-A1000 multimeter offers.
  • NCV MODE: use the non-contact voltage (NCV) mode to safely test for hot/live wires. Simply line up the multimeter with the power source. Beeping indicates electrical current.
  • HIGH RANGE AND PRECISION: featuring both manual and auto modes, true RMS readings at 4x/S, and safe measurements up to 1000V, confidently diagnose automotive, industrial, and household electrical...
  • CONVENIENT FEATURES: like a kickstand, a large LCD backlit screen, data hold, auto shut-off, and a hook clip, you can take and record measurements with ease.
  • OVERLOAD PROTECTION: Overload protection is active on all ranges. Built-in F600mA/1000V and F10A/1000V explosion-proof ceramic fuse tubes offer twice the protection compared to multimeters with only 1...

Conclusion

This was all about ohmmeters for now. I hope this article was useful and helped you in understanding about the working of an ohmmeter.

I have a couple of more measuring devices for you as well. In order to know more about these measuring instruments, keep visiting the blog.

Thanks for reading my articles,

Nasir.

3 Comments

Leave a Comment