There’s a wide range of accessories for your压力仪器that can help make your process safer, more efficient and precise. Snubbers, dampeners, capillaries, pressure limiting valves, siphons and other accessories are common additions to the most challenging applications.
One question I’ve heard often during my time in this industry is: do these accessories impact the accuracy of pressure measuring instruments?
在本文中，我将讨论许多共同之处pressure instrument accessories今天可用，他们如何工作，以及它们的使用方式或者如何影响测量的准确性。
什么因素影响压力仪器的准确性？
首先，让我们潜入能够影响准确性的问题。有很多方法可以影响压力仪器，我们已经详细介绍了“仪器杀手“ 文章。
These factors include:
- Excessive pulsation/vibration
- Extreme low/high temperatures
- Pressure spikes
- Instrument clogging
- 仪器腐蚀
Next, we’ll go deeper into these factors and discuss the accessories and instrument assemblies designed to help counteract these negative effects on your pressure instrumentation. Knowing how they work can help you understand how they may impact accuracy.
What Are the Different Pressure Instrument Accessories?
Theasme.B 40.100 Standards Guide identifies several types of accessories that protect the performance and integrity of pressure gauges from harsh conditions such as pulsation, vibration, pressure spikes, clogging and/or corrosion.
这些配件还可以帮助其他压力测量仪器，例如压力开关和换能器。
Flow Restrictors
Pulsation can damage equipment or cause inaccurate readings. In processing equipment, surges in process pressure can lead to pulsation in gauges. These pulsations can cause poor gauge readability due to pointer flutter and decreased gauge integrity due to component damage.
Pressure snubbers and pulsation dampenersare used to lessen the effects of pulsation.These accessories dissipate pulsation before it reaches the instrument by restricting the flow of the process material.
其他流动限制器如针阀and throttle screws can change the size of the opening on a pressure instrument to combat pulsation. Some accessories are more adjustable than others.
Needle valves can be opened wide or closed to control flow, much like a spigot for a garden hose. Throttle screws thread into the communication hole of a pressure gauge and shrink it down from a standard hole to a pinhole, which effectively controls the impacts of pulsation.
压力浪涌可能会导致速度超出最大允许的工作压力，这可能会损坏仪器以外的修理。Pressure limiting valvesclose once the pressure reaches a set point and only reopen when it’s safe again to protect the gauge.
例如，if you had a pressure gauge installed on a system that typically operated at 10 psi, you would ideally be using a 0-30 psi range. If the system could potentially experience higher pressures (over 38 psi), either during a clean down process or a pressure test, it could damage the gauge.
在这种情况下，可以将压力限制阀设定为靠近30psi，并且测量仪将保持保护，直到压力降至安全水平。
Pressure switches can also be assisted by the use of a pressure limiting valve. Pressure switches are mechanical devices and can be limited to percentages of span on where the setpoints can be.
例如,0 - 100 psi开关可以设置点s between 15 and 90 psi. If you have a system that operates at 80 psi, you will want a switch with a span of 0-100 psi (or higher). If you need a 5 psi decreasing set point, your switch may not be able to accommodate because you’re limited to 15-90 psi.
解决这一点的一个策略是具有压力限制阀。您可以使用30psi的压力限制阀门使用0-30psi的跨度使用开关。这将允许您安全地在80 psi（在这种情况下，压力限制阀将闭合保护开关）。
When the pressure decreases below 30 psi, the pressure limiting valve opens allowing the switch to operate. And a 0-30 psi switch can achieve the 5 psi decreasing set point.
Extreme Temperature Protection
仪器还需要防止极端温度。例如，coil siphonsare designed for steam applications. They help protect gauges from high-temperature steam by creating a condensate barrier and isolating the instrument from the steam.
In other extreme temperatures applications, acapillarycan help keep instruments safe from damage. One part of the capillary connects to the process and the other connects to the gauge allowing you to mount the gauge somewhere safe away from the extreme temperatures of the process.
Capillaries also help reduce the temperature by reducing the volume of the media passing throughand allowing the ambient temperature to cool (or heat) the media.
However, capillaries can get clogged easily. Because capillaries have a small communication hole they also act as effective flow restrictors and can help with pulsation. They also provide flexibility with where instruments are mounted, so where there is heavy vibration an instrument can be relocated to a more stable environment.
In applications that would be prone to clogging you may need to protect the capillary with an isolation device known as a diaphragm seal or isolation ring.
防止堵塞和腐蚀
Diaphragm seals and isolation rings旨在保护仪器免受堵塞和腐蚀。它们安装在仪器（以及相关配件）和过程之间。
它们使用转移流体（由薄膜或衬里的偏转引起的偏转）的位移将工艺压力传递给仪器。
They can be constructed from many different types of materials for applications that use harsh chemicals, or with larger openings and more robust sensing elements to protect against particulates in the process.
Can Instrument Accessories Impact Accuracy?
Now that you have a rundown of the various pressure instrument mounting accessories and what they’re used for, do any of them impact the accuracy of your measurements?
简短的答案是，大多数人都没有。
Flow restrictors such as pulsation dampeners, snubbers, throttle screws, needle valves and especially capillary would likely impact the response time on registering a pressure reading, but it would not impact the accuracy of the instrument.
应用的流量限制越多，您可以期望的响应时间越长。但最终，减慢响应时间是使用流量限制器的所需结果。通过减慢响应时间，您可以有效地减少压力脉动的影响。
Diaphragm seals, however, can impact accuracy. The seals require additional pressure to displace their fluid, which can affect the accuracy of your pressure measurement.
的位移和弹簧刚度the diaphragm must be enough to actuate the sensing mechanism of the instrument. Because the diaphragm has a finite spring rate, it will require some pressure to displace the fluid necessary to operate the pressure element.
This impact on accuracy will be greater on instruments with elements requiring more fluid displacement，隔膜具有较高的弹簧速率，以及较低压力范围仪器。最佳做法是用附着的密封重新校准仪器。
由于温度波动导致填充流体的膨胀或收缩，液体填充隔膜密封件也可能在压力测量中产生可检测误差。您需要在过程服务和环境温度下校准密封和仪器，以确保精确度，并使暴露于外部温度/元素暴露的任何部件。
适用于ASME代码规范的可靠，高质量的压力仪器将有助于确保您从压力测量中获得最准确的读数。
阿什克罗夫特的压力仪表组件指南良好的优质仪器安装产品选择，有助于保持压力测量仪器有效，安全，准确地运行，无需担心设备故障。
我们不喜欢对你施压，但我们有更多信息。
You should now have a better understanding of what pressure instrument accessories can be used for and whether they have an impact on the accuracy of your pressure measurements.
If you want more information on these types of mounting accessories and assemblies, view our webinar about压力仪器安装组件.
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