Digital Amplifiers

Electronic amplifiers are used with analog meters to increase their ranges, to make them more sensitive, to improve their accuracy, and to minimize their effects on the circuit under test. But, any analog meter movement can be used effectively without amplifiers; they need only multiplier resistors and/or shunt resistors to work on different ranges.

Continue reading “Digital Amplifiers”

Electromagnetic Meter Construction: Part 2


In both the moving-coil and moving-iron meter movements, the current being measured flows through the coil. Except for this similarity, the coils in each type of movement are different. When current flows through the coil of the moving-coil meter movement, a magnetic field is produced that causes the coil to rotate. For the coil to rotate easily, it must be as light as possible. To make the coil light, it is wound on an aluminum frame. Furthermore, the coil is made from very fine wire, and when compared with the coil in the other meter movements, it contains very few turns to keep it as light as possible.

Continue reading “Electromagnetic Meter Construction: Part 2”

More Special-Purpose Meters


The oscilloscope was developed over 50 years ago. As a piece of test equipment, it was one of the most exciting advances in electrical testing at that time and still is. Ordinary analog and digital meters merely give numerical quantities, whereas the oscilloscope does that and in addition, gives a graphic picture of what the test signal looks like. The shapes, frequencies, amplitudes, phases, distortions, interference, and so on, all show up to be examined. One cycle or less of an AC signal, or multiple cycles, or even a stream of cycles can be examined. DC levels and combinations of DC and AC can be viewed.

Continue reading “More Special-Purpose Meters”

Meter Sensitivity and Accuracy

Every meter coil has a certain amount of dc resistance. The amount of resistance depends upon the number of turns on the coil and the size of the wire used to wind the coil. The strength of the magnetic field about a coil increases as the number of turns of the coil increases. Therefore, if more windings are placed on a meter coil, a small current can create a magnetic field strong enough to cause the coil to deflect full scale.

Continue reading “Meter Sensitivity and Accuracy”

Resistance Testing: Part 1

There are several different types of resistance tests. Resistance tests differ from voltage and current tests because they are rarely performed on a dynamic basis, that is, while the equipment is operating. Resistance tests are usually performed with the power off and usually with the component disconnected to make sure that there are no short circuits to cause misleading readings.

Continue reading “Resistance Testing: Part 1”