10 Questions - Pressure Transmitters

How much do you know about pressure transmitters? Are you accurately, quickly and reliably measuring pressure? Ultimately, the drive of any good pressure transmitter is to get an accurate, reliable pressure measurement to the data user quickly. This video gives you the answers to your basic questions about pressure and pressure transmitters.

### 转录

Hi my name is Lee Hamlett, I'm with Yokogawa, I'm a product manager I've been here 12 years.

What is pressure?

Well pressure is very simple, its just the amount force applied over a certain area. This can apply to gas, liquid, anything that applies a certain force over a certain amount of area. well pressure is one of the four unique measurements inside of a plant. The others being flow, temperature and level. What unique about pressure is pressure can actually be used to infer the other three. Flow by using a pressure transmitter across a Venturi, a Pitot tube or a orifice plate you can infer what the flow of the liquid or gas that you are measuring. With level in a tank, you can use the hydrostatic head pressure principle to measure the amount of liquid in a tank. Lastly and not used very much is, using pressure to measure temperature. This is where you have a certain amount of gas in a closed area and as the temperature changes, the pressure inside the chamber changes and by the change of pressure you know the change in temperature is.

What are some basic traits of pressure that are important in industrial applications?

Well theres three attributes that are important. First , in a chamber the pressure is the same no matter where your located inside the chamber, so whether you're at the top, the bottom, the left the right, the pressure is the same no matter where you're at in the chamber. The second attribute is if you have the same amount of gas in a chamber, you change the size of the chamber the pressure changes in the chamber to meet the size you've changed to, so if you make a smaller chamber, the pressure increases. The third attribute is the way that temperature affects pressure, if we have a given size chamber with a gas in it and you increase the temperature, the pressure will increase in it or if you decrease the temperature the pressure will decrease. Those three attributes are very important to know.

What is pressure reference?

Well when you measure pressure what you're really doing is comparing two pressures to each other and theres a couple ways to qualify that . Theres a gauge pressure measurement that compares the pressure that you are measuring to the atmospheric pressure. Now thats very similar to what you do with your car tire, when you measure the pressure in your car tire you actually comparing the pressure in the tire to the outside of the tire. The problem with that is if theres any change in the local pressure it can look like your accuracy is off, and pressure changes when a thunderstorm comes through, a cold front or anything like that. The local atmospheric pressure can change. Now the next one is absolute pressure. Thats where you compare your pressure you are wanting to measure to absolutely zero pressure. Zero pressure doesn't exist anywhere, so its very hard to build a transmitter that references, you have to suck the vacuum out of the of a chamber to compare to. Thats very good because it doesn't have the variation that you get with gauge pressure. Problem is they are very expensive. Some customers will put up with using a gauge reference  because its less expensive or instead of the absolute pressure thats more accurate. And then theres also a differential pressure reference and thats where you're just comparing two separate pressures.

How do you measure pressure in an industrial application?

Well you use a pressure transmitter. Pressure transmitters have sensors in them that are designed to measure the pressure. How they do that, is they have a physical attribute in the sensor that changes when pressure changes. So you're actually measuring the change of that physical attribute to infer what the pressure change is. theres several different ways of doing that, theres sensors on the market that use frequencies, capacitance and inductance. They are all kinds of sensors out there and you can find transmitters that use all the different technologies.

Is that all a pressure transmitter does?

No. The transmitter takes information from the sensor and transmits it or communicates with something else that  needs the information. That can be a controller , a DCS or even a cloud based data collection program. Whats important is that the transmitter do it quickly, accurately and reliably. Thats whats important.

How does the transmitter communicate?

Well most transmitters are hardwired to whatever needs the information but there also wireless solutions out there that broadcast the information to where it needs to go.

What language does the transmitter communicate in?

Wells theres two, theres an analog communication and theres also a digital or a combination of the two. Analog you have a 1-5 volt DC or 4-20 milliamp signal that corresponds to the variation in the pressure. With digital you have a protocol and thats a language that the controller and transmitter speak with each other to get the information. Some popular versions of this are HART, FieldBus, MODBUS. Some companies even have a proprietary communication language. There is a lot to chose from but make sure all of your equipment speaks the same language.

What characteristics should you look for in a pressure transmitter?

As we discussed before, you want your transmitter to quickly, accurately and reliably get the signal to where it needs to go. Unfortunately, with a lot of pressure transmitters out there the specifications that convert to these qualities are hard to understand. When it comes to quickly, you're looking for response time. You want a fast response time. With accuracy, thats easy, thats usually referred to as reference accuracy. The one that is a little tough to understand is reliability which has to do with the stability of the product. So what you want to look for is the response time, the accuracy and the stability of the transmitter you are looking at.

Anything else you should look for?

All applications and all pressure transmitters are different. all sensors all manufactures, everybody has their strengths and weaknesses. You just need to evaluate what your application needs and pick the unit that best suits your application.

A good source of information would be yokogawa.com/us there you'll find these questions and answers as well as other things that you can use to help you evaluate transmitters.

• ### 上游

上游行业包含海上和陆上活动，包括井口自动化、分馏、完井和分离，回收和制备地下或水下原油和天然气

当石油被带到地表时，在运输之前必须将其分离。在三相分离中，一级和二级分离阶段通常分布有气体流量、水流量和油流量。气体的输送需要管道，并且在输送之前的上游阶段需要进行分馏。液体需要通过罐和管道输送并处理，这就需要精确的液位测量

更多
• ### 化工

化工厂依靠连续和批量的生产过程，每个生产过程对控制系统都有不同的要求。连续的过程需要一个强大而稳定的控制系统，该系统不能因为自身失效而导致生产线关闭；批量过程的重点在于拥有一个可以灵活调整公式程序的控制系统。两种系统都需要在产品质量记录中进行管理，并且能够执行非常规操作。横河电机凭借广泛的产品组合、经验丰富的系统工程师、遍及全球的销售和服务网络，为每个工厂流程提供解决方案。

更多
• ### 污水处理

污水处理厂使用大量的电动机、泵、鼓风机等，因此降低其耗电量以降低运营成本是十分重要的。横河电机提供控制解决方案，以提高能源效率。

更多
• ### 海水淡化

海水淡化作为一种稳定的水资源需求日益增长。横河电机在控制各种类型的海水淡化工厂方面拥有丰富的经验，例如RO (反渗透)、MSF (多级闪蒸)和MED (多效蒸馏)。

更多
• ### 生物燃料

为了阻止全球变暖的趋势，生物燃料的生产和需求在全球范围内呈上升趋势。化工、石油其他工业领域中，横河电机拥有卓越的测量和控制解决方案，并且已经开发出用于生物乙醇和其他可再生燃料领域的技术，确保生产过程的可靠性和高效性。

更多
• ### 生物质发电

现在生物质受到越来越多的关注，因为它是一种可再生能源，可以帮助火力发电厂减少二氧化碳排放。横河电机的系统在世界各地各种类型的发电厂中都有使用，包括使用生物质发电的工厂。横河电机的测量和控制技术帮助这些工厂更有效地运行并减少其碳排放。

更多

石油和天然气

更多
• ### 管道

能否正确控制管道和仪表会在性能和盈利方面会产生巨大的差异。横河拥有专业的技术，可以优化管道解决方案中所有因素的性能，包括压缩机、泵、阀门及中间存储和分配设施。

更多
• ### 精炼

在不断变化的市场中，炼油厂不仅是原油加工单位，而且是利润中心。同时，人们强烈意识到炼油厂设施安全性的重要。为了实现盈利、效率及环境保护的长期目标，需要包括计划、调度、管理和控制的总体生产解决方案。凭借在自动化领域多年积累的专业知识，横河可以为您提供经济实惠的完善的整体解决方案，改善操作并使世界更清洁。

更多
• ### 造纸

面对不断变化的市场需求，造纸行业的竞争也愈演愈烈。横河电机可以帮助节能工厂实现全球可持续性发展。

更多

• ### 压力变送器

使用横河电机的压力变送器，可以对过程压力进行准确且稳定的测量，支持安全、可靠和可盈利的工厂运营。

更多