The system to be analyzed is a simple ringoffive configurati

The system to be analyzed is a simple ring-of-five configuration, as shown in the schematic view of Fig- ure 6.1. Because the initial \"state\" of the inverter gate outputs in this circuit is not deterministic, we can assist our future analysis of this circuit by replacing one of the pure inverters with a \"controllable\" inverter, as shown in Figure 6.2. When the ctrl input to the NAND gate in this circuit is held \"low\" (a logic 0), the output of the NAND must be a \"high\" (a logic 1), and the ultimate outputs of the remaining gates are easily resolved, if enough time is allowed to ensure propagation delay through all gates. Then we can remove the ctrl input, by switching it to a logic 1, and can then observe the \"astable\" but predictable time changes of each and every input and output. gout[1] gout[2] gout[3] gout[4] gout[5] FIGURE 6.1 Schematic diagram of basic ring-of-five sequential circuit. gout[1] gout[2] gout[3] gout[4] gout[5] ctrl . FIGURE 6.2 Schematic diagram of basic controlled ring-of-five sequential circuit

Solution

In a DC motor, an armature rotates inside a magnetic field. Basic working principle of DC motor is based on the fact that whenever a current carrying conductor is placed inside a magnetic field, there will be mechanical force experienced by that conductor. All kinds of DC motors work in this principle only. Hence for constructing a DC motor it is essential to establish a magnetic field. The magnetic field is obviously established by means of magnet. The magnet can by any types i.e. it may be electromagnet or it can be permanent magnet. When permanent magnet is used to create magnetic field in a DC motor, the motor is referred as permanent magnet DC motor or PMDC motor. Have you ever uncovered any battery operated toy, if you did, you had obviously found a battery operated motor inside it. This battery operated motor is nothing but a permanent magnet dc motor or PMDC motor. These types of motor are essentially simple in construction. These motors are commonly used as starter motor in automobiles, windshield wipers, washer, for blowers used in heaters and air conditioners, to raise and lower windows, it also extensively used in toys. As the magnetic field strength of a permanent magnet is fixed it cannot be controlled externally, field control of this type of dc motor cannot be possible. Thus permanent magnet DC motor is used where there is no need of speed control of motor by means of controlling its field. Small fractional and sub fractional kW motors now constructed with permanent magnet.