1-4
Figure 1-2.—Simpson 260 multimeter.
Two obvious advantages of the Simpson 260 are its portability and ease of operation. Among its
disadvantages are its low input impedance and the inherent low accuracy associated with D’Arsonval
meter movements, which are used in the meter. When performing measurements with any analog
multimeter, remember that the most accurate readings are taken with the pointer midscale. You should
also be aware of inaccuracies introduced as a result of parallax. PARALLAX is defined as the apparent
displacement of the position of an object because of the difference between two points of view. In the
case of meters, this means the position of a meter’s pointer will appear to be at different positions on the
scale depending on the angle from which the meter is viewed. Some of the Simpson 260 and 270 series
multimeters have effectively eliminated the problem of parallax by incorporating a mirror on the scale
that accurately reflects the position of the pointer of the meter movement.
Q-4.
At what point on a meter movement are the most accurate readings taken?
Oscilloscope Method
A dc voltage measurement can be made with an oscilloscope, as shown in figure 1-3, that has a
direct-coupled deflection amplifier or terminals for connection directly to the deflection plates of the
cathode-ray tube. Measuring a dc voltage with an oscilloscope is convenient only under certain
circumstances; for example, when other measurements are being made on the same equipment with the
oscilloscope or when a vacuum tube voltmeter is not available and a high-impedance measuring device is
required.
