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.
轉錄
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.
Where can I find more information?
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.
產業別
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上游
上游業包含海上和陸上活動，包括井口自動化，分餾，完井和分離，回收和製備地下或水下原油和天然氣。
當石油被帶到地表時，在運輸之前必須將其分離。在三相分離中，一級和二級分離階段通常分佈有氣體流量，水流量和油流量，氣體的輸送需要管道，並且在輸送之前的上游階段需要進行分餾。液體需要通過罐和管道輸送並處理，這就需要精確的液位測量。
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化工
化工廠依靠連續和批量的生產製程，每個生產製程對控制系統都有不同的要求。連續的製程需要一個強大而穩定的控制系統，該系統不能因為自身失效而導致生產線關閉；批量製程的重點在於擁有一個可以靈活調整地公式和程序的控制系統。兩種系統都需要在產品質量記錄中進行管理，並且能夠執行非常規操作。橫河電機憑借廣泛的產品組合、經驗豐富的系統工程師、遍及全球的銷售和服務網絡，為每個工廠流程提供解決方案。
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生物燃料
為了阻止全球變暖的趨勢，生物燃料的生產和需求在全球範圍內呈上升趨勢。在化工、石油及其他工業領域中，橫河電機擁有卓越的測量和控制解決方案，並且已經開發出用於生物乙醇和其他可再生燃料領域的技術，可確保生產製程的可靠性和高效性。
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生物質發電
現在生物質受到越來越多的關注，因為它是一種可再生能源，可以幫助火力發電廠減少二氧化碳排放。橫河電機的系統在世界各地各種類型的發電廠中都有使用，包括使用生物質發電的工廠。橫河電機的測量和控制技術幫助這些工廠更有效地運行並減少其碳排放。
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石油和天然氣
石油和天然氣
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管道
能否正確控制管道和儀表會在性能和盈利方面會產生巨大的差異。橫河擁有專業的技術，可以優化管道解決方案中所有因素的性能，包括壓縮機，泵，閥門及中間存儲和分配設施。
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精煉
在不斷變化的市場中，煉油廠不僅是原油加工單位，而且是利潤中心。同時，人們強烈意識到煉油廠設施安全性的重要。為了實現盈利，效率及環境保護的長期目標，需要包括計劃，調度，管理和控制的總體生產解決方案。憑藉在自動化領域多年積累的專業知識，橫河可以為您提供經濟實惠的完善的整體解決方案，改善操作並使世界更清潔。
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造紙
面對不斷變化的市場需求，造紙行業的競爭也愈演愈烈。橫河電機可以幫助節能工廠實現全球可持續性發展。