关于压力开关的常见问题

了解系统动力学对于开关选择至关重要。 目标是获得 在寿命、准确性、可靠性和易用性方面满足您期望的 压力开关。 在这里， Barksdale 回答了您在为特定应用选择理想压力开关时应该提出的所有问题。

压力开关多久启动一次？

这将对开关寿命、系统停机时间和大修计划产生直接影响。 机电开关 易受金属疲劳的影响。 波登管或隔膜开关通常会提供一百万次循环。 而活塞或隔膜密封活塞开关将提供 2-1/2 百万次循环。 由于固态压力开关不受金属疲劳的影响，它通常具有 1 亿次循环寿命。

循环速度是多少？

波登管或膜片开关的金属就像弹簧一样，因此应避免高速循环。 当循环速率低于每分钟 25 次时，波登管或隔膜开关是不错的选择。 对于每分钟 50 次循环的循环速率，隔膜活塞或活塞开关将分别提供 1 到 2-1/2 百万次循环。 只要循环率超过每分钟 50 次，就应该选择固态开关，因为金属疲劳不是问题。

开关点与工作压力范围有何关系？

选择开关点和开关工作压力范围 之间的适当关系 很重要，因为这种关系会影响精度和使用寿命。 固态和机电压力开关的一般规则是不同的。 选择固态压力开关时，开关点通常应在工作范围的较高25％。 对于机电开关，开关点应在工作范围的中间。

耐压要求是多少？

证明压力是开关应该看到的最大压力。 在计算 开关耐受压力 时，包括尖峰和浪涌以避免损坏开关。

压力开关会受到高压尖峰和浪涌的影响吗？

压力波动和瞬时压力峰值可能大大超过系统的正常工作压力。 波登管、隔膜和固态压力开关都对浪涌和尖峰敏感。 如果预计系统会受到冲击，请选择具有更高耐压的开关或安装一个缓冲器，以允许快速尖峰通过开关移动而不会损坏。

需要什么精度？

压力开关的精度与仪器的精度不同。 对于压力开关，精度是开关在其设定点重复操作的能力。 如有疑问，指定可用的最佳精度总是更容易。

需要多少个开关点？

在某一点感应压力时，只需要一个开关点是正常的。 然而，系统需要两个甚至四个开关点（例如高、低、高-高、低-低）来监控、控制或报警的情况并不少见。 在设计系统时，您可以为每个开关点选择一个开关，或者一个能够处理多达三个独立开关点的压力开关。

需要什么类型的外壳？

裸线开关没有自己的外壳。 它们通常安装在面板或多功能外壳内。 外壳开关避免了暴露位置的松散电线可能造成的危险，通常有多种额定值可供选择，最流行的工业开关外壳是 NEMA 4 和 NEMA 4X，适用于腐蚀性环境。

是否需要调整设定值？

在某些应用中，您不希望任何人更改设定值。 在其他情况下，需要根据系统动态进行调整。 机电开关的型号为出厂设置，具有盲调节功能，或提供校准的调节旋钮。 固态开关通过数字读数提供精确的键盘调整。

需要紧死区还是宽死区？

死区是压力驱动开关中的驱动点和重新驱动点之间的差异。 死区 有时被称为驱动值、差分或滞后。 开关的死区可以在整个压力范围的某个百分比上固定或调整。 传统上，安全服务使用窄死区。 更宽的死区用于液压装置等控制回路。 波登管和膜片开关的死区较窄或较窄，活塞式开关的死区较宽，而固态开关的死区可完全调节至满量程的 100%。

精度还是寿命？

选择 固态压力开关 时，精度和寿命之间没有权衡。 您只需选择开关点位于压力范围上 25% 的压力开关即可。 机电开关具有不断受到压力的传感元件（隔膜、管和活塞），因此开关点的位置与工作范围的关系对于精度和寿命都至关重要。 最好的折衷办法是在操作范围的中间操作机电压力开关。 Barksdale 的新型 BPS3000 电子压力开关是 Generation 3000 系列的一部分，具有无与伦比的精度。

是否需要更多功能而不仅仅是一个开关？

很多时候，系统需要的不仅仅是一个压力开关来打开和关闭一个电路。 可能还需要本地仪表和远程信号。 传统方法是使用单独的设备。 然而，基于微处理器的固态压力开关改变了动态。 一个固态开关最多可提供四个独立开关、数字读数和模拟/数字输出。

有关 Barksdale 全系列开关产品的更多信息，请联系 010-84282935 或访问 www.barksdaleproducts.com。

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.barksdaleproducts.com. .