關(guān)于壓力開關(guān)的常見問題

了解系統(tǒng)動力學(xué)對于開關(guān)選擇至關(guān)重要。 目標(biāo)是獲得 在壽命、準(zhǔn)確性、可靠性和易用性方面滿足您期望的 壓力開關(guān)。 在這里， Barksdale 回答了您在為特定應(yīng)用選擇理想壓力開關(guān)時應(yīng)該提出的所有問題。

壓力開關(guān)多久啟動一次？

這將對開關(guān)壽命、系統(tǒng)停機時間和大修計劃產(chǎn)生直接影響。 機電開關(guān) 易受金屬疲勞的影響。 波登管或隔膜開關(guān)通常會提供一百萬次循環(huán)。 而活塞或隔膜密封活塞開關(guān)將提供 2-1/2 百萬次循環(huán)。 由于固態(tài)壓力開關(guān)不受金屬疲勞的影響，它通常具有 1 億次循環(huán)壽命。

循環(huán)速度是多少？

波登管或膜片開關(guān)的金屬就像彈簧一樣，因此應(yīng)避免高速循環(huán)。 當(dāng)循環(huán)速率低于每分鐘 25 次時，波登管或隔膜開關(guān)是不錯的選擇。 對于每分鐘 50 次循環(huán)的循環(huán)速率，隔膜活塞或活塞開關(guān)將分別提供 1 到 2-1/2 百萬次循環(huán)。 只要循環(huán)率超過每分鐘 50 次，就應(yīng)該選擇固態(tài)開關(guān)，因為金屬疲勞不是問題。

開關(guān)點與工作壓力范圍有何關(guān)系？

選擇開關(guān)點和開關(guān)工作壓力范圍 之間的適當(dāng)關(guān)系 很重要，因為這種關(guān)系會影響精度和使用壽命。 固態(tài)和機電壓力開關(guān)的一般規(guī)則是不同的。 選擇固態(tài)壓力開關(guān)時，開關(guān)點通常應(yīng)在工作范圍的較高25％。 對于機電開關(guān)，開關(guān)點應(yīng)在工作范圍的中間。

耐壓要求是多少？

證明壓力是開關(guān)應(yīng)該看到的最大壓力。 在計算 開關(guān)耐受壓力 時，包括尖峰和浪涌以避免損壞開關(guān)。

壓力開關(guān)會受到高壓尖峰和浪涌的影響嗎？

壓力波動和瞬時壓力峰值可能大大超過系統(tǒng)的正常工作壓力。 波登管、隔膜和固態(tài)壓力開關(guān)都對浪涌和尖峰敏感。 如果預(yù)計系統(tǒng)會受到?jīng)_擊，請選擇具有更高耐壓的開關(guān)或安裝一個緩沖器，以允許快速尖峰通過開關(guān)移動而不會損壞。

需要什么精度？

壓力開關(guān)的精度與儀器的精度不同。 對于壓力開關(guān)，精度是開關(guān)在其設(shè)定點重復(fù)操作的能力。 如有疑問，指定可用的最佳精度總是更容易。

需要多少個開關(guān)點？

在某一點感應(yīng)壓力時，只需要一個開關(guān)點是正常的。 然而，系統(tǒng)需要兩個甚至四個開關(guān)點（例如高、低、高-高、低-低）來監(jiān)控、控制或報警的情況并不少見。 在設(shè)計系統(tǒng)時，您可以為每個開關(guān)點選擇一個開關(guān)，或者一個能夠處理多達(dá)三個獨立開關(guān)點的壓力開關(guān)。

需要什么類型的外殼？

裸線開關(guān)沒有自己的外殼。 它們通常安裝在面板或多功能外殼內(nèi)。 外殼開關(guān)避免了暴露位置的松散電線可能造成的危險，通常有多種額定值可供選擇，最流行的工業(yè)開關(guān)外殼是 NEMA 4 和 NEMA 4X，適用于腐蝕性環(huán)境。

是否需要調(diào)整設(shè)定值？

在某些應(yīng)用中，您不希望任何人更改設(shè)定值。 在其他情況下，需要根據(jù)系統(tǒng)動態(tài)進行調(diào)整。 機電開關(guān)的型號為出廠設(shè)置，具有盲調(diào)節(jié)功能，或提供校準(zhǔn)的調(diào)節(jié)旋鈕。 固態(tài)開關(guān)通過數(shù)字讀數(shù)提供精確的鍵盤調(diào)整。

需要緊死區(qū)還是寬死區(qū)？

死區(qū)是壓力驅(qū)動開關(guān)中的驅(qū)動點和重新驅(qū)動點之間的差異。 死區(qū) 有時被稱為驅(qū)動值、差分或滯后。 開關(guān)的死區(qū)可以在整個壓力范圍的某個百分比上固定或調(diào)整。 傳統(tǒng)上，安全服務(wù)使用窄死區(qū)。 更寬的死區(qū)用于液壓裝置等控制回路。 波登管和膜片開關(guān)的死區(qū)較窄或較窄，活塞式開關(guān)的死區(qū)較寬，而固態(tài)開關(guān)的死區(qū)可完全調(diào)節(jié)至滿量程的 100%。

精度還是壽命？

選擇 固態(tài)壓力開關(guān) 時，精度和壽命之間沒有權(quán)衡。 您只需選擇開關(guān)點位于壓力范圍上 25% 的壓力開關(guān)即可。 機電開關(guān)具有不斷受到壓力的傳感元件（隔膜、管和活塞），因此開關(guān)點的位置與工作范圍的關(guān)系對于精度和壽命都至關(guān)重要。 最好的折衷辦法是在操作范圍的中間操作機電壓力開關(guān)。 Barksdale 的新型 BPS3000 電子壓力開關(guān)是 Generation 3000 系列的一部分，具有無與倫比的精度。

是否需要更多功能而不僅僅是一個開關(guān)？

很多時候，系統(tǒng)需要的不僅僅是一個壓力開關(guān)來打開和關(guān)閉一個電路。 可能還需要本地儀表和遠(yuǎn)程信號。 傳統(tǒng)方法是使用單獨的設(shè)備。 然而，基于微處理器的固態(tài)壓力開關(guān)改變了動態(tài)。 一個固態(tài)開關(guān)最多可提供四個獨立開關(guān)、數(shù)字讀數(shù)和模擬/數(shù)字輸出。

有關(guān) Barksdale 全系列開關(guān)產(chǎn)品的更多信息，請聯(lián)系 010-84282935 或訪問 www.qaxozkz.com.cn。

Frequently asked questions about pressure switches

Understanding system dynamics is crucial to switch selection. The goal is to obtain a pressure switch that will meet your expectations in terms of life, accuracy, reliability, and ease of use. Here, Barksdale answers all the questions you should be asking when choosing the ideal pressure switch for your particular application.

How often will the pressure switch be activated?

This will have a direct impact on switch life, system downtime and the overhaul schedule. Electromechanical switches are subject to metal fatigue. A bourdon tube or diaphragm switch will typically provide one million cycles. Whereas a piston or diaphragm sealed piston switch will provide 2-1/2 million cycles. Because a solid-state pressure switch is not subject to metal fatigue, it will typically have a 100 million cycle life.

What is the cycle speed?

The metal of a bourdon tube or diaphragm switch acts like a spring, so high-speed cycles should be avoided. When the cycle rate is less than 25 per minute, a bourdon tube or diaphragm switch is a good choice. For cycle rates to 50 cycles per minute, a diaphragm piston or piston switch will provide 1 to 2-1/2 million cycles, respectively. A solid-state switch should be selected whenever the cycle rate exceeds 50 cycles per minute, since metal fatigue is not a problem.

How does the switch point relate to operating pressure range?

Selecting the proper relationship between the switch point and the operating pressure range of a switch is important because this relationship can affect accuracy and useful life. The general rule is different for solid-state and electromechanical pressure switches. When a solid-state pressure switch is selected, the switch point should normally be in the upper 25 per cent of the operating range. For an electromechanical switch, the switch point should be in the middle of the operating range.

What is the proof pressure requirement?

Proof pressure is the maximum pressure that the switch should ever see. When calculating the switch proof pressure , include spikes and surges to avoid damage to the switch.

Will the pressure switch be subjected to high-pressure spikes and surges?

Pressure surges and transient pressure spikes can greatly exceed the normal operating pressure of a system. Bourdon tube, diaphragm and solid-state pressure switches are all sensitive to surges and spikes. If it is anticipated that the system is subject to surges, select a switch with a higher proof pressure or install a snubber which will allow fast spikes to move by the switch without damage.

What accuracy is needed?

Accuracy for a pressure switch is defined differently than accuracy for an instrument. For a pressure switch, accuracy is the ability of the switch to repetitively operate at its setpoint. When in doubt, it is always easier to specify the best accuracy available.

How many switch points are needed?

When sensing pressure at one point, it is normal that only one switch point is required. However, it is not unusual for a system to require two or even four switch points (e.g. high, low, high-high, low-low) to be monitored, controlled or alarmed. In designing a system, you could select a single switch for each switch point, or a single pressure switch capable of handling as many as three separate switch points.

What type of housing is needed?

Stripped switches don't have their own housing. They're normally installed inside a panel or multi-function enclosure. Housed switches avoid possible hazards from loose wires in exposed locations and are normally available in a variety of ratings, with the most popular industrial switch housings being NEMA 4 and NEMA 4X for corrosive environments.

Is there a need to adjust the setpoint?

In some applications, you wouldn't want anyone changing the setpoint. In other situations, adjustment is required based on system dynamics. Electromechanical switches have models that are factory set, have blind adjustment capability, or offer calibrated adjustment knobs. Solid-state switches offer precise keypad adjustments with digital readout.

Is a tight or broad deadband needed?

Deadband is the difference between the actuation point and the re-actuation point in a pressure actuation switch. Deadband is sometimes referred to as actuation value, differential or hysteresis. The deadband of a switch can be fixed or adjusted over a percentage of the full pressure range. Traditionally, a narrow deadband is used in safety services. A wider deadband is used on control circuits like hydraulic units. Tight or narrow deadbands tend to be found on bourdon tube and diaphragm switches, wide deadbands are available in piston-type switches, while solid-state switches offer a fully adjustable deadband to 100 per cent of full scale.

Accuracy or life?

When selecting a solid-state pressure switch there is no trade-off between accuracy and life. You simply choose a pressure switch where the switch point is in the upper 25 per cent of the pressure range. Electromechanical switches have sensing elements (diaphragms, tubes and pistons) that are constantly being stressed and thus the location of the switch point versus the operating range is critical to both accuracy and life. The best compromise is to operate the electromechanical pressure switch in the middle of the operating range. Barksdale's new BPS3000 electronic pressure switch, part of the Generation 3000 range, offers unrivalled accuracy.

Are more features needed than just a switch?

Many times the system requires more than a pressure switch to open and close a circuit. A local gauge and remote signal may also be required. The traditional approach is to use individual devices. However, microprocessor-based solid-state pressure switches change the dynamics. One solid-state switch can offer up to four independent switches, digital readouts and analog/digital outputs.

For more information about Barksdale's full range of switch products please contact 010-84282935 or visit www.qaxozkz.com.cn. .