Types of Relays 继电器的类型（上）

天狼晓月

Types of Relays 继电器的类型（上）


         There are many types of relays, each designed for a particular purpose. Among the more common types are electromechanical, contactor, dry reed, mercury wetted reed, and solid state. Table 2-2 compares some key parameters by relay type.

       继电器有多种类型，每种类型都是针对特定的目的设计的。在常见的类型中，包括机电式、接触器式、干簧式、水银继电器和固态继电器。表 2 2按照继电器类型列出了几个关键的参数。

表2-2 继电器对比表

NOTES

注释

1.     For a complete off-on-off cycle.

             一个完整的“关－开－关”周期。

       2.     Mercury is listed as a banned substance under the Restrictions of Hazardous Substances (RoHS) Directive, therefore limiting the application of these relays.

              根据《限制电器及电子设备使用有害物质(RoHS)》规范，水银被列为被禁用物质，从而限制使用这类继电器。

2.2.1 机电式继电器

        Electromechanical relays have a coil of wire with a rod passing through the middle (forming an electromagnet), an armature mechanism, and one or more sets of contacts. When the coil is energized, the electromagnet attracts one end of the armature mechanism, which in turn moves the contacts. Figure 2-2 shows a typical electromechanical relay with the main operating elements labeled and a scheme for actuating the armature.

        机电式继电器有一个中间穿过一根金属棒的线圈（形成一个电磁铁）、一个枢轴机构和一组或多组触点组成。当线圈受到激励时，磁铁就会吸引枢轴机构的一端，从而移动触点。图2-2所示为一个典型的机电式继电器，其中标出了主要的工作元件以及激励枢轴机构的示意图。

图2‑2Figure 2-2. Electromechanical relay (armature)

图 2-2 机电式继电器（枢轴衔铁）

        The coil must generate a strong field to actuate the relay completely. Several parammeters contribute to the determination of the force necessary to actuate the relay, among them:

        线圈必须产生一个强磁场来完全地激励继电器。有几个参数决定了激励继电器所需的强度，其中包括：

• 触点间距。（Spacing of the contacts.）
• 触点所在的材料的弹簧常数。 （Spring constant of the material on which the contacts are mounted.）
• 枢轴机构的重量。 （Mass of the armature mechanism.）

        (More information on coil design can be found in the Engineers’ Relay Handbook, 5th edition, National Association of Relay Manufacturers, 1996.)Electromechanical relays are available in configurations ranging from 1 Form A or B to 12 or more Form C. This type of relay can be operated by AC or DC signals and can switch currents up to 15 amperes, as well as relatively low level voltage and current signals.

        （关于线圈设计的更多信息请参阅《Engineers’ Relay Handbook》第5版，National Association of Relay Manufacturers, 1996）机电式继电器可被配置为从1个A或B型式到12或更多个C型式配置。这种类型的继电器可使用交流或直流信号进行工作，并且开关电流可高达15 A，并且电压和电流信号相对较低。

        Electromechanical relays are available in non-latching and latching types. Non-latching relays return to a known state when power is removed or lost. Latching relays, such as those on several Integra Model 770X cards, remain in their last position when relay drive current is removed or lost. Return mechanisms (for non-latching relays) and latching mechanisms can be magnetic or mechanical, such as a spring.

        机电式继电器既可是非闭锁型，又可是闭锁型。非闭锁型继电器在关闭或断开电源时其返回的状态是已知的；而闭锁型继电器，如几款779X型集成开关卡上的继电器，当继电器的激励电流被关闭或断开时，仍然会保持其最后的位置状态。回行机构（对于非闭锁型继电器）和闭锁机构可以是磁性的或机械的，例如弹簧。

        Since latching relays do not require current flow to maintain position, they are used in applications with limited power. Also, the lack of coil heating, which minimizes contact potential, makes latching relays useful in very low voltage applications.

        由于闭锁继电器不需要电流来维持其位置，因此被用于功率有限的应用中。此外，由于线圈不会发热，从而使接触电势最小化，使得闭锁型继电器被广泛用于电压非常低的应用中。

2.2.2 机电式继电器（高频）

        Materials and physical configuration of relays determine inherent capacitances among their components. For example, the capacitance between poles degrades AC signal isolation by coupling the signal from pole to pole or relay to relay. These capacitances within relays are a common factor that limit the frequency of switched signals.

        继电器的材料和物理配置决定了其元件间的固有电容。例如电极之间的电容会对从电极到电极或从继电器到继电器之间的信号产生耦合，从而劣化了交流信号的隔离。

        Specialized contacts and architecture are used in electromechanical relays to obtain good performance for RF and microwave switching up to 40GHz. A typical configuration is shown in Figure 2-3, where the common terminal is between two switched terminals. All signal connections are coaxial to ensure signal integrity.In this case, the connectors are the female SMA type. For more complex switching configurations, the common terminal is surrounded by switched terminals
in a radial pattern.

        专用的触点和机构被用于机电式继电器中来获得高达400 GHz的射频（RF）和微波的切换性能。一种典型的配置如图2-3所示，其中，共用端子介于两个开关端子之间。所有的信号都是同轴连接的，以确保信号的完整性。在本例中，连接器为雌头SMA型。对于更加复杂的切换配置，共用端子是被呈放射状的开关端子所环绕的。

图2‑3Figure 2-3. Electromechanical relay (high frequency)

图 2-3 机电式继电器（高频）

2.2.3 接触器

        A contactor is a special type of electromechanical relay, where the contacts are attached to the armature. This type of relay is used to switch currents greater than a few amps and power levels of several hundred to several thousand watts.

        接触器是一种特殊类型的机电式继电器，其触点被安装在枢轴机构上。这种类型的继电器被用于切换大于几个安培的电流，功率从几百瓦到数千瓦。

        The large physical size and limited isolation (due to materials requirements and construction) make this type of relay a poor choice for signal switching.

        较大的物理尺寸和受限的隔离（由于材料和构造的要求）使这类继电器不适合于信号切换。

2.2.4 干簧继电器

        Dry reed relays are also operated by energizing a coil, but in this type of relay, the coil is wound around the switch so that the induced magnetic field closes the switch. Figure 2-4 shows a simplified representation of a typical reed relay.

        干簧继电器也是靠激励一个线圈进行工作的，但是在这种类型的继电器中，线圈环绕着开关，从而感应的磁场使开关闭合。图 2-4所示为这典型的干簧继电器的简化图。

图2‑4Figure 2-4. Reed relay

图 2-4 干簧继电器

        The switch is made from two thin, flat strips of ferromagnetic material called reeds, with contacts on the overlapping ends. Leads are connected to the outside ends of the reeds and the entire assembly is sealed in a hermetic glass tube. The tube holds the leads in place (with a small gap between the contacts for normally open switches). See Figure 2-5.

        开关是由两个扁平的磁性材料薄片组成的，这两个薄片被称为簧片，触点位于簧片上相互搭接的一端。导线被连接至簧片的外侧一端，并且整个成套件是被密封在一个密闭的玻璃管内。玻璃管将导线固定在位置上（对于常开开关，触点之间有一个小的气隙）。请参见图 2-5。

图2‑5Figure 2-5. Dry reed relay

图 2-5 干簧继电器

        Normally closed switches, less common than normally open, are made in one of two ways. The first method is to make the switch so that the contacts aretouching each other. The second method uses a small permanent magnet to hold normally open contacts together. The field from the coil opposes the field of the magnet, allowing the contacts to open.

        常闭开关没有常开开关那么常见，它是采用两种方式之一制成的。第一种方法是使开关的触点彼此保持接触；第二种方法是采用小的永久磁铁使常开触点闭合在一起。线圈形成的磁场抵消掉磁铁的磁场之后，既可是触点打开。

        In order to reduce the oxidation of contacts greatly (or eliminate it), the environment inside the glass tube is often pressurized with a gas that contains no oxygen. A good general-purpose gas has about 97% nitrogen and 3% hydrogen. For high voltage switching (above 500V), the glass tube is evacuated. Although more costly, this provides the highest standoff voltage switch.

        为了大幅度降低（或者消除）触点的氧化，玻璃管内的环境往往是采用不含氧气的气体加压的。一种较好的通用气体含大约97%的氮气和3%的氢气。对于高电压开关（高于500 V），玻璃管则是被抽空的。这种方法尽管成本较高，但是能够提供最高的关态电压开关。

        To lower the characteristic capacitance and leakage currents of reed relays (and, less commonly, electromechanical relays), an electrostatic shield is sometimes added between the switches and the coil. The shield is typically metal foil that is terminated to a pin connected to some low impedance point in the circuit. Common low impedance connection points are signal low and guard.

        为降低干簧继电器（以及并不那么常见的机电式继电器）的特征电容和漏泄电流，有时会在开关和线圈之间增加一层静电屏蔽。屏蔽物通常为金属线圈，该线圈被端接至连接到电路中某个低阻抗点的管脚上。常见的低阻抗连接点为信号低电平和保护线路。

        An electromagnetic shield can also be added around the outside of the coil. This type of shield keeps the field generated by the energized coil from interfering with other components. It also protects the switch so that random state changes do not occur due to external EMI. (Electromagnetic shields are not placed between the coil and switch since they “protect” the switch and prevent operation.) This type of shield is connected in the same way as an electrostatic shield.

        在线圈的外侧也可以增加一层电磁屏蔽。这种类型的屏蔽能够防止线圈加电后产生的磁场干扰其它组件。它还能保护开关不会因为外部电磁干扰（EMI）而发生状态变化（在线圈和开关之间不能增加磁场，否则该磁场会“保护”起开关，并妨碍其工作）。这种类型屏蔽的连接方式与静电屏蔽是相同的。

        The high permeability of the ferromagnetic reeds in a reed relay causes a pronounced skin effect with increasing signal frequency. Skin effect is current conduction along only the outer surface of a conductor at high frequencies. This causes a dramatic increase in resistance and a decrease in inductance. Signal frequencies carried by reed relays are usually limited to 10MHz or less due to this effect.

        干簧式继电器中铁磁簧片的高磁导率会随信号频率的增加而产生很强的趋肤效应。趋肤效应是指在高频下仅通过导体的外表面进行传导的电流。这会造成明显的电阻增大和电感减小。由于这一效应的影响，干簧式继电器所能承载的信号频率通常被限制在10 MHz或更低。

        Isolated contacts and low operating power make reed relays an ideal choice for many signal switching applications.

        干簧式继电器的隔离触点和低工作电流使其成为了多种信号切换应用中的理想选择。