Woodward 82510 磁性拾音器和接近开关

磁速传感器(MPU)用于检测原动机的速度。当原动机驱动其他东西而不是交流发电机时，MPU是必要的。它也经常用于交流发电机直接由原动机驱动，当一个控制信号是必要的交流发电机达到其适当的输出电压。需要一个速度传感器电路，要么是调速器放大器底盘上的一个部分，要么是一个单独的单元，将MPU的输出信号转换为调速器放大器可用的信号。
当任何磁性材料穿过拾音器末端的磁场时，磁性拾音器产生电压输出。由于大多数发动机和涡轮机都有由磁性材料(通常是铁或钢)制成的飞轮或其他大型齿轮，磁性拾音器通常可以安装在齿轮或轴上，而无需添加附件。非磁性材料，如铝、黄铜和一些不锈钢，不会激发磁性拾音器。
MPU利用“杂散磁场”，不需要提供返回磁路或路径。在拾音器的磁场中产生磁性材料的动态不连续的任何装置都会产生电压。虽然齿轮是MPU测量的正常设备，但如果考虑到表面速度和其他因素，其他设备如振动表面，移动杆，曲柄，轮辐或安装在某些移动表面上的钢螺钉头也会同样工作。微处理器可以通过键槽或轮毂槽来激发，但由于材料的密度或偏心的变化，可能会有不需要的背景信号。最好是用表面上的突起来激励微处理器。这使得拾音器在激发周期之间离材料相对较远的地方，并且它不太可能拾取杂散信号。
磁拾音器的输出电压受三个因素的影响:
·电压随着被监测磁性材料表面速度的增加而增加。
●随着磁性拾音器与齿轮齿表面之间的气隙增加，电压降低。
·电压波形由齿轮齿的尺寸和形状与极片的尺寸和形状的关系决定。
在任何给定的速度和间隙条件下，当磁场在某一时刻充满相对无限大质量的磁性材料，而下一时刻完全没有这种材料时，将产生最大功率输出。当激振质量的横截面等于或大于极片的横截面，且两者之间的间距等于或大于极片直径的三倍(见图1-1)时，存在一种合理的方法来满足这些条件。

Woodward 82510

The magnetic speed pickup (MPU) is used to detect the speed of the prime mover. An MPU is necessary when the prime mover drives something other than an alternator. It is also often used where an alternator is driven directly by the prime mover and when a control signal is necessary before the alternator comes up to its proper output voltage. A speed sensor circuit, either a section on the governor amplifier chassis or a separate unit, is needed to convert the MPU’s output signal to one usable by the governor amplifier.
The magnetic pickup produces a voltage output when any magnetic material moves through the magnetic field at the end of the pickup. Since most engines and turbines have flywheels or other large gears made of magnetic material (usually iron or steel), magnetic pickups can usually be installed without adding attachments to a gear or shaft. Nonmagnetic materials, such as aluminum, brass, and some stainless steels, will not excite the magnetic pickup.
The MPU makes use of a “stray magnetic field” and no provision for return magnetic circuits or paths is necessary. Any device which produces a dynamic discontinuity of magnetic material in the field of the pickup will produce an electrical voltage. Although gears are the normal devices measured by an MPU, other devices such as a vibrating surface, moving bar, crank, wheel spokes, or a steel screw head mounted on some moving surface will work equally well if surface speed and other factors are taken into account. The MPU may be excited by a keyway or slot in a wheel, but there is likely to be an unwanted background signal due to varying density or eccentricity of the material. It is better to excite the MPU from a protrusion on the surface. This places the pickup at a relatively great distance from the materials between excitation periods and it is less likely to pick up stray signals.
The output voltage of a magnetic pickup is affected by three factors:
 Voltage increases as the surface speed of the monitored magnetic material increases.
 Voltage decreases as the air gap between the magnetic pickup and the surface of the gear tooth is increased.
 Voltage waveform is determined by the size and shape of the gear tooth in relation to the size and shape of the pole piece.
With any given speed and clearance conditions, a maximum power output will result when the field is filled with a relatively infinite mass of magnetic material at one instant and a complete absence of such material the next. A reasonable approach to these conditions exists when the cross-section of the exciting masses is equal to or greater than that of the pole piece, and the space between is equal to or greater than three times the diameter of the pole piece (see Figure 1-1).