Ac Measurement
Chapter 13
AC MEASUREMENT
This chapter explains rectification for measurement and rectifying instruments. Knowledge of the circuit principles will help you use these instruments properly and measurements alternating current correctly. One of the most common and economical methods for measuring alternating currents is to rectify these currents and read the resultant DC on an analog or digital volt-ohm meter (VOM). You need to take many considerations into account when using rectification: what type of rectification you use, what scale conversion you will need, and the sensitivity of the meter.
RECTIFICATION
Alternating current periodically changes direction, which is why it is called alternating current. Direct current, on the other hand, maintains one direction or polarity of current. Rectification is the process of changing an alternating current into a direct current. Whether we use one direction (half cycle or half wave) or both directions (full cycle or full wave) is determined by the circuitry.
THE DIODE
In half-wave rectification only one diode is used. As you will recall from previous chapters, a diode is a check valve for electrical current. Current may flow only in one direction through a diode. It obtains its name from di-, meaning two, and -ode for electrodes. The electrodes are named the anode (positive electrode) and cathode (negative electrode). There are many different kinds of diodes. We will restrict ourselves here to just two types, germanium and silicon. The only differences between the two that are significant to us will be the: 1. Voltage necessary to maintain current flow in the positive direction—approx. 0.1 to 0.3 for germanium, approx. 0.5 to 0.9 for silicon.
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2. Peak inverse voltage rating (explained in the text). 3. Power-handling capability (silicon is far more capable). Figure 13–1 represents a diode schematically. Current flow is shown as electronic (negative to positive). The
AC MEASUREMENT
This chapter explains rectification for measurement and rectifying instruments. Knowledge of the circuit principles will help you use these instruments properly and measurements alternating current correctly. One of the most common and economical methods for measuring alternating currents is to rectify these currents and read the resultant DC on an analog or digital volt-ohm meter (VOM). You need to take many considerations into account when using rectification: what type of rectification you use, what scale conversion you will need, and the sensitivity of the meter.
RECTIFICATION
Alternating current periodically changes direction, which is why it is called alternating current. Direct current, on the other hand, maintains one direction or polarity of current. Rectification is the process of changing an alternating current into a direct current. Whether we use one direction (half cycle or half wave) or both directions (full cycle or full wave) is determined by the circuitry.
THE DIODE
In half-wave rectification only one diode is used. As you will recall from previous chapters, a diode is a check valve for electrical current. Current may flow only in one direction through a diode. It obtains its name from di-, meaning two, and -ode for electrodes. The electrodes are named the anode (positive electrode) and cathode (negative electrode). There are many different kinds of diodes. We will restrict ourselves here to just two types, germanium and silicon. The only differences between the two that are significant to us will be the: 1. Voltage necessary to maintain current flow in the positive direction—approx. 0.1 to 0.3 for germanium, approx. 0.5 to 0.9 for silicon.
215
216 Chapter 13—AC MEASUREMENT
2. Peak inverse voltage rating (explained in the text). 3. Power-handling capability (silicon is far more capable). Figure 13–1 represents a diode schematically. Current flow is shown as electronic (negative to positive). The