the rotor is split into two parts, anupper and lower. One half is the north side of the magnet andone is the south. The teeth are offset so that when the teeth of one magnetare lining up with the mating teeth on the stator, the teeth on the other arelining up with the grooves, the tops of the teethare crosshatched for clarity). Some hybrid steppers have more than one stackof magnets for more torque. 2. There are two types of stator winding methods forstepper motors: bipolar and unipolar. Bipolar windings use field coils with no common connections. The coils must be driven independently to reverse the direction of motor flow and rotate the motor. Unipolar motors use coils with centertaps. The centertap is usually connected to the positive supply, and the individual coils are grounded (through transistors) to drive the motor. Each time the field is changed in a bipolar motor or a different coil isturned on in a unipolar motor, the motor shaft steps to the next rotation position
when gaining or losing an electron. The addition of an electron produces a negative ion (-) while loss of an electron converts it to a positive (+) one. Nature provides a delicate balance of ions. The relatively low natural ion levels do not permit systematic evaluation of their biologic properties. A different medium must be artificially created in laboratory and clinical experiments to permit such investigations. Only with the help of ion generators capable of producing unipolar ions in controlled concentrations can this goal be achieved. In medicine, the main interest centers on the effects of artificially created, and not on natural ion levels.. .15 BIOLOGIC CHANGES............................................................................................................15 Excitation or violent attraction or ejection of free electrons from the atoms is responsible for many changes of the target material. It has been found that molecules are held together stably
a magnetic field. They drive the output active when a certain magnetic strength (the operate point) is sensed, then drive the output inactive when the magnetic field drops below a certain level (the release point). There is some hysteresis in the range, where the release point is less than the operate value. 82 Analog Interfacing to Embedded Microprocessors Figure 3.24 The Hall effect. Hall effect switches come in two varieties: unipolar and bipolar, which are sometimes called nonlatching and latching. Bipolar switches have a positive (south pole) operate point and a negative (north pole) release point. Unipo- lar switches have a positive (south pole) operate point and a less-positive release point. The operate and release points vary with temperature. Both bipolar and unipolar switches typically have an open-collector output that has to be pulled up with an external resistor.
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