The ohmmeter or ohmmeter is an electronic device that measures the resistance of an electronic component or circuit. It consists of a numbered scale with a needle indicator or a digital display, a range selector and two probes. In this article, we will explain its basic operation.
Steps
Step 1. Completely disconnect and / or turn off the entire circuit you are testing
In order to preserve the accuracy of the measurements, as well as your safety, it is necessary to have a non-powered electrical wire or circuit. Your ohmmeter will supply the circuit voltage and current, so no additional power is needed. As the instructions of the Blue Point brand device we are using for our test state, taking measurements of a powered circuit can "cause damage to the multimeter, to the circuit and to the user himself".
Step 2. Select a suitable device for your project
Analog ohmmeters are very simple and inexpensive. They usually range from 0 - 10 to 0 - 10,000 ohms. The digital ones can work on similar ranges or they can use an "auto range", detecting the resistance of your device or circuit and automatically selecting the most appropriate range.
Step 3. Check the ohmmeter to see if it has a battery
If you have just bought it, you can find it pre-installed battery inside or packaged separately with installation instructions.
Step 4. Insert the test plugs into their slots on your device
For multifunctional meters, you will see one plug marked as "common" or "negative" and one as "positive". They can also be colored black (-) and red (+) respectively.
Step 5. Reset your tester if it has a zero dial
Note that the scale reads in the reverse direction of the more conventional measurement scales: less resistance on the right and more resistance on the left. You should see zero resistance as the pins are connected together. The correct procedure for adjusting the zero is just to keep them in contact and rotate the adjustment dial until the needle reaches the zero ohm value on the scale.
Step 6. Choose the circuit or electrical device to be tested
For practice, you can use almost anything that conducts electricity, from a piece of tinfoil to a pencil mark on a sheet of paper. To get an idea of the accuracy of your readings, purchase a few different resistors from an electronics supplier or some other device with a known resistance value.
Step 7. Touch one end of a circuit with a probe and the opposite end with the other and check how much the instrument detects
If you bought a 1,000 ohm resistor, you can place a probe on each end of the conductor, selecting the range of 1,000 or 10,000 ohms. Then check the meter to see if it actually measures 1,000 ohms.
Step 8. Isolate the components in a wired electrical circuit to test them individually
If you are reading the values of a resistor placed on a printed circuit board, you will need to unsolder or unblock the resistor to make sure you don't get a false reading measured through another circuit path.
Step 9. Read the resistance of a piece of electrical wire or branch of a circuit to see if there is a short circuit or not
If you detect a resistance of infinite value, it means that the electric current cannot follow any path: in simple terms, this value suggests the existence of at least one component burned somewhere in the circuit or of a non-functioning conductor. Since many circuits contain "gate" devices (transistors or semiconductors), diodes and capacitors, however, continuity cannot be detected even when the complete circuit is intact, which is why it is difficult to test complete circuits with just an ohmmeter.
Step 10. Turn off the ohmmeter when not in use
Occasionally the cables may short-circuit while the device is stored in its box, discharging the battery.
Advice
- If you are thinking of making an investment in a general purpose ohm meter, perhaps it is best to choose a good quality multimeter that can also test other electrical quantities, such as voltage and amperage.
- Familiarize yourself with electrical and electronic terminology and circuit diagrams, as well as reading block diagrams or electrical systems.
- It is good to know that even if a resistor is 1000 ohms declared, in reality its value could differ by up to 150 ohms below or above. Small resistances will differ by minimum values, larger ones by larger quantities.
- Try many different electrical conductivity experiments. Draw a line on a sheet of paper with a graphite pencil and point the probes at both ends of the stroke: you should detect an electric current.
- To learn how to distinguish your ohmmeter ranges, buy a good number of different resistors and test each according to its stated value.
