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    In the process industry valves and actuators are historically used for controlling and diverting fluid flows. Increasingly the plant engineers want a feedback signal of the current position of valves, taps and actuators in the control system. This feedback is generally obtained by use of inductive sensors which are built into a switchbox, or double sensors which are mounted directly on actuators or the manual valve. This article gives an insight in to the type of sensors that are applied in the field and the emerging trends in the market. 在過程工業中，閥門和驅動器一貫用于液體流動的控制和轉移。越來越多的工廠工程師希望在器控制系統中得到閥門、龍頭、及驅動器當下位置的反饋信號。通常這種信號由內置于開關盒中的接近傳感器，或直接安裝在驅動器或手動閥門上的雙傳感器來獲取。本文深入探討在現場和市場新趨勢中應用的傳感器類型。

    State of the Art with Regard to Standardisation 標準化現狀

    Industry standards can be viewed as both positive and negative toward technology development. On the one hand they limit creativity but on the other side they ensure that the apparatus of several manufacturers is compatible. The VDE/VDI 3845 standard describes, amongst other things, the important mechanical connection between pneumatic actuators and the apparatus which must be connected to it. The standard includes a defined mounting hole pattern of 30x80mm and of 30x130mm. Stem heights are 20, 30 and 50 mm. For stem diameter there is no fixed standard, therefore in the case of double sensors you must pay particular attention to this. 行業標準對于技術的發展而言利弊共存。一方面，它限制了創造性，但另一方面他們又確保了不同制造商的設備具備兼容性。VDE / VDI3845標準要求了諸多事項后，規定了氣動驅動器機與所連接設備之間的重要機械連接。該標準包括了對安裝孔的定義：30x80mm和30x130mm。安裝桿的高度為20，30和50毫米。對于安裝桿直徑，則沒有固定的標準，所以在雙傳感器的應用中，用戶必須特別注意。

    The Switchbox開關盒

    The term “switchbox” commonly describes the integration of sensors, cam and connectors in an enclosure, through which the mechanical connection is also made between the sensors and pneumatic actuator. This solution was designed so as not to expose the sensors to the immediate environment and influences, and to be able to use standard sensors (see fig 1). In these standard boxes, the following sensors are typically built in: 術語“開關盒”通常描述在一個封閉盒中傳感器、凸輪和連接器的集成。傳感器和氣動執行器通過它實現機械連接。該解決方案旨在避免傳感器在周邊環境中的暴露或受到影響，同時能夠使用標準傳感器（見圖1）。在這些標準開關盒中，典型內置以下傳感器：


• Cylindrical sensors with a typical construction length of 40mm
• Slot sensors
• Rectangular sensors in V3 style (similar to the micro switch)
• Double sensors which are compact enough to be built in a box (see fig 2)
•圓柱型傳感器，典型長度為40毫米
•槽形傳感器
•矩形V3風格傳感器（類似于微動開關）
•雙傳感器，結構緊湊置于一個盒中（見圖2） 

    The box is used as a terminal compartment to connect the valve position sensor and solenoid. Encoded connections are already on the circuit board, as well as the necessary LED’s. The circuit board fits in most standard boxes.
開關盒被用作終端設備來連接閥位傳感器和電磁閥。編碼的連接器以及必要的LED指示燈已經置于電路板上。電路板的尺寸適合大多數標準盒子。

    The Open Solution開放式解決方案

    The term “open solution” describes the direct mounting of double sensors on automated or manual valves (see fig 3). Two inductive sensors mounted one on top of another in one housing give a precise indication of the open and closed position of a valve. 術語“開放式解決方案”規定了自動閥或手動閥上的雙傳感器安裝（見圖3）。兩個電感式傳感器疊加安裝于一個外殼中，精確顯示了閥門的開關位置。

    The design of this system takes into account the VDE/VDI 3845 standard. The sensors are activated by two stainless targets mounted at 90 degrees to each other on a “puck”. The puck itself is mounted by one screw on the actuator stem. 該系統的設計考慮了VDE / VDI 3845標準。這些傳感器由兩個90度垂直安裝于“圓盤”上的不銹鋼目標觸發。圓盤本身通過一個螺絲釘安裝在執行器上。 

    Apart from compact size and very simple assembly, we find the following advantages: 除了體積小巧，組裝簡單，我們還發現以下優點： 

• Round mounting holes (not slots) in the sensor housing avoid incorrect mounting distances or movement through impact or vibration which otherwise may require maintenance.
• The different alternatives of pneumatic actuators are covered by only two switching elements (pucks). The only choice which must be made is the mounting pattern, e.g. 30x80 or 30x130 (see fig 4 and fig 5)
• Switching targets in stainless steel are already built in to the puck (see fig. 3).
• Four LED’s indicate the output situation of the sensors, the presence of power and the output status of the solenoid valve.
• Thanks to the narrow detection area of the double sensor, there is no danger of a pinch point causing harm to the operator or allowing clogging from ice or dirt.
• The wiring of the solenoid valve can be routed through the sensor so that no separate cable needs to be run to the field.

•傳感器外殼上的圓形安裝孔（非槽形）可避免由于錯誤的安裝距離或運動而導致的碰撞或震動引起的維修。
•兩個開關元件（圓盤）可以適應多種不同的氣動執行器。唯一需要做出的選擇是安裝模式，例如： 30x80或30x130（見圖4和圖5）
•不銹鋼的目標物已經設計在圓盤上。（見圖3）。
•4個LED等表明該傳感器的輸出情況，電源有無和電磁閥輸出狀態。
•雙傳感器的檢測區域足夠狹窄，因而不會產生擠壓點導致操作人員受傷，或冰塊、灰塵形成的堵塞。
•電磁閥的接線，可經過傳感器進行布線，現場無需單獨電纜。

Inductive Sensors Versus Mechanical Switch電感式傳感器與機械開關
In all areas of industry where the mechanical switch was previously a much-used solution for a diversity of control problems, nowadays the approach has changed. The sensor is now the solution. This is a consequence of the ability of sensors to offer significant speed and reliability advantages: 在工業的所有領域中，機械開關曾經一度是各種控制問題的方案首選，而如今的方法已今非昔比，傳感器毋庸置疑為首選。因為傳感器的工作速度和可靠性的優勢十分明顯：

- Entirely solid state, as a result, no wear and tolerance modifications.
- Faster output switching
- Hysteresis and repeatability can be defined electronically much more successfully than in a mechanical device.
- No welding or corrosion of output contacts.
- Little or no influence of clogging or humidity.
- No contact bounce (output echo)
- LED indication on most sensors to show when the sensor has switched. This makes maintenance and commissioning simpler and quicker.

- 全固態，因此無磨損或誤差修改
- 快速輸出開關狀態
- 磁滯和重復性可以比機械設備更多得進行電子定義
- 無焊接或輸出端腐蝕
- 很少或根本不受堵塞或濕度的影響
- 無觸點抖動（輸出回波）
- 大多數傳感器切換時有LED顯示。使得維護和調試更簡單，快捷。

    Typically the average life span of an inductive sensor is considerably longer than those of a mechanical switch. The fact that historically, very many mechanical switches were used for valve feedback is partly due to the difference in price and partly the fact that when using a switch polarity does not need to be considered. By use of modern techniques, Pepperl+Fuchs have succeeded in bringing sensors to the market which eliminate those remaining advantages of mechanical switches.

    通常，一個電感式傳感器的平均壽命大大超過機械開關。事實上，過去很多機械開關都用于閥門反饋，是由于價格的低廉，同時也因為我們在使用開關時極性問題不需要考慮。通過現代技術，倍加福已經成功地將傳感器推向市場，消除了機械式開關僅有的一點優勢。

Possible Sensors for Valve Position Detection用于閥位檢測的傳感器

Choosing the correct sensor can be achieved in 5 simple steps: 選擇正確的傳感器可按以下5個簡單步驟實現：

    Step 1: Switchbox or open solution? 步驟1：開關盒或還是開放式解決方案？

    Weigh the aforesaid advantages and disadvantages against each other and make the choice. You either require the protection that the switchbox gives, or the simplicity and convenience of an open solution. Most valve suppliers offer as a matter of course the two solutions. You will find that switchboxes come in all sizes and weights, and in several qualities and classes.

    權衡上述優勢與缺點，做出選擇。您可能需要開關盒的保護，或開放式解決方案的簡單便捷。大多數閥門供應商都會提供兩種解決方案。你會發現開關盒的體積和重量都各異，數量與種類也大相徑庭。

    Step 2: Define electrically the final termination a sensor will have to the control system which regulates the process (AC, DC, Namur etc.). Of overriding importance is whether the system is used in an explosive area. We see the following electrical connection types. 步驟2：電氣定義傳感器的終端，傳感器所連接的控制系統調節著工作過程（交流，直流，Namur等）。極為重要的一點是該系統是否在爆炸地區使用。我們看以下的電氣連接類型。

• Three wire DC Sensors. These sensors have a separate wire beside the two wires for powering the sensor. The third wire is the output which is connected to the PLC input card or the control system. 直流三線傳感器。這些傳感器在兩條供電線路外還有一條單獨的線路。第三條線路連接到PLC輸入卡或控制系統上的輸出端。

• Two Wire DC sensors. Here the load is connected in series with the sensor. Many of these sensors are polarity tolerant which means that it does not matter how the wires are connected. For this reason, it is exactly the same as how you would connect a normal mechanical switch. In applications using these type of sensors, you must pay attention to the off state current in the circuit and the voltage drop of the sensor. 直流兩線傳感器。在這里，負載與傳感器串聯。許多傳感器都具備極性容差，即無需再關心接線的極性。因此，它與連接正常的機械開關一樣簡單。實際應用這類傳感器，您一定要注意電路的漏電流及傳感器的電壓降。

    • AC voltage with Normally Open (NO) and/or Normally Closed contacts. (NC). Here the load is in series with the sensor. 帶有常開（NO）和/或常閉輸出的交流傳感器。在這里，負載與傳感器串聯。

    • Two Wire universal Voltage. The sensor is connected in series with the load. Either AC Voltage or DC Voltage can be connected. 交直流兩線通用傳感器。該傳感器與負載串聯。無論交流電壓或直流電壓均可連接。

     • Two Wire NAMUR; with an associated intrinsically safe barrier, these can be used in areas with an explosive atmosphere (area 0, 1 and 2). Lead breakage and short circuit monitoring are possible as standard. 兩線Namur傳感器，與相關本安產品一起，用于防爆環境（區域0，1和2）。可實現斷線及短路監測。

     • Two Wire Failsafe sensors. As per two wire Namur but subject to use of a safety rated barrier, a SIL 3 approved circuit is obtainable. 兩線故障安全傳感器。按兩線Namur傳感器標準，但是使用滿足安全級別的隔離柵，可以達到SIL3 安全等級。

    Step 4: Connection possibilities第4步：連接的可能性

    The manner of connection depends on the philosophy of the end-user. Such as, glands with cables or plug termination. For example, the chemical and pharma sector tend to choose cable connection by means of glanded entry to the box or sensor. 連接方式取決于最終用戶。例如，帶電纜的密封管或插頭。化學和制藥領域傾向于選擇電纜連接，通過電纜密封管進入盒子或傳感器。

    Step 5: Operation of the solenoid valve步驟5：電磁閥操作
Just like with the switchbox, one also has the option with double sensors to wire the solenoid by means of the sensor. The advantage lies in the fact that there is then only one cable that must be laid to the actuator與開關盒一樣，使用雙傳感器也可以經過傳感器進行電磁閥的布線，其優勢就在于執行器只需要一根電纜連接。

    Finally, one must verify a number of general properties of the sensor to be certain the sensor will function perfectly in the application. 最后，您必須確認傳感器的諸多特性以確保傳感器在應用中完美運行。

    Some examples of this are the off state current, voltage drop, environmental surroundings, maximum output current and operating voltage.

    If possible one can verify by means of the specifications of the selected sensor also if quiescent current (disturbances), shock and vibration maximum values are not exceeded.類似的例子便是漏電流、電壓降，周圍環境，最大輸出電流和工作電壓。 如果可能，您可以通過選定傳感器的規格來確認，保證在靜態電流（干擾），沖擊和振動最大值的允許范圍內。

    Trends and Future Developments未來的發展

    Because installations are very often adapted to the newest technology in order to work more efficiently and reliably, all kind of bus systems have entered the market. 由于安裝過程經常要適應最新的技術發展，以提高工作效率和穩定性，各種總線系統開始進入市場。

    Of course producers of switchboxes and actuators want to anticipate this and we see that a number of these manufacturers have developed interfaces, in consultation with sensor manufacturers, to these bus systems. A good example of this is switchboxes with AS interface incorporated because this bus system is particularly suitable for digital information. If the end user wishes to use standard sensors, appropriate field mountable modules can be found for AS_interface, Profibus PA or foundation Fieldbus (see fig6).

    開關盒和執行器的生產商當然希望加入。我們看到許多這樣的制造商已經與傳感器制造商協商開發出了這些總線系統的接口。帶AS-i的開關盒便是一個很好的例子，因為這種總線系統特別適合數字信息。如果最終用戶希望使用標準傳感器，便需要合適的現場安裝模塊，如AS-interface，Profibus PA或基金會現場總線（參見圖6）。

    On the other hand we see also electric actuators and positioners used with Profibus or foundation Fieldbus interface. It seems that more and more companies are realising the advantages of bus systems and particularly the combination of a field bus (for example Profibus) with AS interface is seen in installations more commonly.

    另一方面，我們也看到使用帶有Profibus或基金會現場總線接口的電氣執行器和定位系統。顯然越來越多的公司意識到總線系統的優勢，特別是帶AS-i的現場總線組合（如Profibus）十分多見。

    Conclusion結論

    We are increasingly seeing inductive sensors replacing the mechanical switch. In some markets, 60-70% of switchboxes are fitted with inductive proximity switches which have replaced mechanical forbearers. For valve position detection standardisation is still some way off. This is due to the original starting point from which switchboxes have been devised and therefore a large mixture of mechanical assemblies and switch technologies exist.

    More commonly, end-users also frequently ask for solutions which lend themselves to greater reliability to allow for long term payback from the switchbox. 我們越來越多感受到電感式傳感器取代機械開關的趨勢。在某些市場，60-70%裝有電感式開關的開關盒已取代了機械式開關。閥位檢測的標準化還有一段路要走。這是因為原來開關盒設計的起點中機械裝配和開關技術的大量混合存在著。更常見的是，最終用戶也經常要求提供更為可靠的解決方案，著眼于開關盒的長期回報。

    Sensor companies have continued development and innovation and it can be seen that an enormous mixture of sensors exist which can be assembled in all kinds of switchbox. 傳感器公司的持續發展和創新使得大量傳感器的混合存在，以便裝配于各種開關盒中。

    In certain industries a clear tendency to the open solution is noticeable due to a price that comes close to that of the switchbox solution with mechanical contacts. Fitting valve position feedback on manual valves now also becomes a more attractive option with the size and cost of the open solution.

    在某些行業領域中，開放式解決方案是一個明顯的趨勢，因為它的價格很接近于機械接觸的開關盒方案。現在由于開放式解決方案的尺寸和成本的優勢，在手動閥上裝配位置反饋也變得更有吸引力。