一个简单的继电器电路消除扫描式电子显微镜的双级制动器中噪声。

　　大多数实验室和工业环境中存在全频率下有多种电子噪声源，主要来自重型设备、器械、能量源和显示器。工程师使用过许多简单设备和技术来处理这种噪声，包括使用适当接地方法、屏蔽和绞电缆、信号平均、差分输入电压放大器和滤波器。

　　虽然这些方法在大多数测量中能控制和减少噪声，但是一些技术只是防止噪声进入系统，而其他只是去除信号中的外来噪声。这些方法通常只在低压系统中使用；不能用于高压系统引起的噪声。

　　本设计方案提供了一种减少高压引起噪声的实用方法。扫描式电子显微镜的浮动输入为高阻抗，就像是天线一样获取

噪声信号。显微镜的激励需要高压信号来驱动它们的压电滑粘防喷器电动机。运动机构需要范围为800V峰峰值的斜坡波形。因为尖端运动有三种程度，所以机构也要多个通道。一些显微镜将原子力显微镜与光程调整的显微镜载片合并，这就需要更多通道。

　　传统上，每通道需要一个高压放大器。所以两维的尖端运动需要两个高压放大器，三维的需要三个高压放大器，以此类推。高压放大器价格昂贵，且需要PCB板上相当大的空间。因此，只使用一个转换多通道间的高压放大器控制多维尖端运动，可以节省价钱和空间。高压连接器管脚间有足够空间，避免干扰邻近信号。但是高压连接器昂贵，且体积过大难以排列。所以最好的选择是使用商业RS-232标准的9/25管脚连接器（图1）。大多数商业RS-232连接器的管脚很接近，容易接收到高压引起的噪声。通过连接一个低阻抗到RS-232连接器的浮动引脚，可以解决这个问题。

　　这个电路中，三个压电发动机PZ₁、PZ₂和PZ₃，连接到RS 232 9T连接器的T₁、T₅和T₉管脚。电路有三个继电器转换压电发动机的高压输入。通常继电器开环节点连接到高压放大器输出；继电器闭环节点连接到三个1 kΩ电阻，将高压引起的噪声旁路到地。

　　英文原文：

　　Relays eliminate high-voltage noise

　　A simple relay circuit cancels noise in the actuator stage of a scanning electron microscope.

　　Jui-I Tsai, Woei-Wu Pai, Feng-Chang Hsu, Po-Jui Chen, Ching-Cheng Teng, and Tai-Shan Liao, National Applied Research Laboratories, Hsinchu, Taiwan; Edited By Charles H Small and Fran Granville -- EDN, 9/13/2007

　　Most laboratories and industrial environments have many kinds of electrical-noise sources at all frequencies from heavy machinery, instruments, power supplies, and TV stations. Engineers have used many simple devices and techniques to handle this noise. These techniques include the use of proper grounding methods, shielded and twisted wires, signal averaging, differential-input-voltage amplifiers, and filters.

　　Although these methods can control and reduce the noise in most measurements, some techniques just prevent noise from entering the system, whereas others remove only extraneous noise from the signal. These methods usually find use only in low-voltage systems; they do not address high-voltage-induced noise.

　　This Design Idea offers a practical approach to reducing high-voltage-induced noise. The floating input of a scanning electron microscope has high impedance, and it acts as an antenna, picking up noise signals. The microscope’s actuators need a high-voltage signal to drive their piezoelectric slip-stick stack motors. The motion mechanism requires a ramping waveform spanning to 800V p-p. The mechanism requires multiple channels because there are three degrees of tip motion. Some microscopes incorporate optical-path-adjustment microsliders for atomic-force microscopy; those scopes need even more channel

s.

　　Traditionally, each channel needs a high-voltage amplifier. So, two degrees of tip motion need two high-voltage amplifiers, three degrees need three amplifiers, and so on. High-voltage amplifiers are expensive and need considerable space on the PCB (printed-circuit board), however. Therefore, controlling multiple degrees of tip motion using only one high-voltage amplifier that switches among multiple channels saves cost and space. The pins of high-voltage connectors have enough space between them to avoid disturbing adjacent signals. But high-voltage connectors are expensive and too large to easily arrange. So, the best choice is to use a commercial RS‑232-standard, nine-pin/25-pin connector (Figure 1). The pins of most commercial RS‑232 connectors are close enough together to easily pick up induced high-voltage signals. You can solve this problem by connecting a low impedance to the floating pins of the RS‑232 connector.

　　In this circuit, three piezoelectric motors, PZ1, PZ2, and PZ3, connect to the T1, T5, and T9 pins of the RS‑232‑9T connector. The circuit has three relays that switch the high-voltage input to the piezoelectric motors. The normally open node of the relays connects to the high-voltage-amplifier output. The normally closed nodes of the relays connect to three 1‑kΩ resistors to bypass high-voltage-induced noise to ground.