An Ohmmeter is an electronic device for the measurement of the quantum of electric resistance in an circuit or an electronic component. The instrument consist of a either a ruled scale with a pointer or a digital display, two probes and a range selector. This article will guide you on the material that you will need, the choosing of the ohmmeter etc.
What You Will Need
- An ohmmeter and some sample resistors or conductors for practice.
The Steps You Will Be Required To Follow Are Detailed Below:
- Depending on the use you are going to put your ohmmeter to, you first have to choose on. The analog instruments are relatively cheaper and the basic models usually come in the reading range of 0 to 10 to 0 to 10,000 ohms. Digital ones may have a similar range or may have an auto-range which gives an automatic reading.
- Some ohmmeters come with a pre-installed battery. Check to see if the one you purchased is such a model. If not, either a battery is provided separately or you may have to purchase one or two as the manual may specify and install it according to the instructions.
- Plug in the leads into the provided sockets in the ohmmeter. Multi-functional will be provided with a common (-) socket and a (+) socket. Typically they will be colored, red for (+) and black for (-).
- Calibrate the meter so that the zero is pointed to perfectly. You’ll probably find that the measuring scales measure less resistances to the left side and high resistances to the right. Calibration is done so that when the two probes are held together, the meter should show a zero reading. If not, then adjust till it does using the adjust dial till it does.
- Select the electrical device or the circuit that is to be tested. Al most anything that conducts electricity can be used as practice material – a small strip of aluminum foil or even a pencil mark on paper. A few different resistors or a device, the resistance value of which is known would be ideal. These will give you an indication of the precision of your readings.
- Connect one of the probes to one end of the circuit and the other probe to the other end. Note the reading. If you are using a 1,000 ohm resistor, a setting to a 1,000 or a 10,000 ohm range should be sufficient to give you an accurate reading.
- When you test a hard wired electrical circuit, it is better that you isolate the component that you are going to test. Remove them from the board so that there is no interference through another route in the circuit.
- A reading of a small length of wire or a branch in a circuit should show you whether there is a short circuit to a break in the circuit. In case the reading shows an infinite value then there is no path in the circuit for the electricity to follow. This, simply stated, means that there is either a burnt out component or a broken conductor somewhere in the circuit. Just an ohmmeter is not sufficient to test circuits completely because of the presence of such devices as the transistor that has gates and capacitors and diodes.
- Switch off the ohmmeter when it is not used. There is the possibility to the test probes to get shorted resulting in a fast drain of the battery.
Some Tips
- To familiarize yourself with the ranges in the ohmmeter, purchase a variety of resistors and test each one of them for their specified resistance.
- There is a possibility for marginal errors and the small one could be off by 150 ohms and the larger ones by a larger amount.
- Experiment with electrical conductivity. If you draw a line on a sheet of paper with a graphite pencil, it should conduct electricity.
- Familiarize yourself with both electronic and electrical terminology. Familiarize yourself also with circuit boards and the reading of wiring(schematic) diagrams.
- A multimeter or a multi-tester will be useful for general purpose testing as it also tests voltage and amperage in addition to resistance.
A word of warning. Before you test any electrical device ensure that it is de-energized. You can do this by unplugging and discharging of any capacitors in any circuit. TVs and other electronic devices equipped with cathode ray tube could be carrying a capacitor that is charges with a thousands of volts even when unplugged.
