#Googleask – Answering 7 questions about pressure measurement

If you want an answer, then you almost always go to Google, right? Just drop in a few keywords to read a bunch of articles and opinions, then draw your conclusions.

Well, I found an efficient way  to peek at what people ask Google. So naturally, I peeked. Then I needed to help those people find quick and direct answers, at least in process automation. Some of those other topics? Y’all are on your own.

Anyway, I wrote this article to provide quick and direct answers on one topic while covering different aspects of it. Today, let’s see what people ask Google about pressure measurement.

1 – What is pressure measurement

We can define pressure as a force applied in a particular area. If you play defense in American football, then you apply force on the guy in front of you to move him so you can reach the ball. You’ll hear sportscasters talk about pressuring the offense. Yep. And if you kick a ball, then your foot applies force to the ball to send it toward the goalposts. Most people just call that the extra point.

Anyway, we use tools to measure pressure because those measurements come in handy in many ways. Of course, you need to know the pressure of certain parts of a process, like in a vessel, pipe, or pump. But if you know about certain types of pressure in a process, then you can learn about other things, like flow.

Did you know you can make perfect fries with pressure? Take a look:

2 – How to measure pressure

We have several ways to measure pressure in process automation, and the best way will depend on various factors. However, I can still give you an idea of what you’ll find on the market.

First of all, you have different types of pressure – differential, absolute, and gauge pressure thus we also have different ways of pressure measurement. We’ll talk more about those in a minute. If you know what kind of pressure you have, then you can choose a manometer for a local reading or a transmitter to send the reading to a system.

  • Manometer: The Bourdon pressure gauge has a flattened tube inside that will straighten or curl depending on how much pressure it detects. This movement is proportional to the pressure in the input.
  • Transmitter:  You can find many types of pressure transmitter. Capacitive pressure transmitters, for instance, will change capacitance based on the input pressure. It too is proportional to the amount of pressure applied to the sensor.

3 –  What is absolute pressure measurement

The different types of pressure we mentioned earlier – differential, absolute, and gauge – all vary by reference. What does that mean? For instance, if you want to measure the pressure between two points, then you need a differential pressure (DP) device. If you need to measure pressure itself, then a gauge device can give you absolute or gauge pressure.

Pressure measurement: Types of pressure

To measure absolute pressure, you use a vacuum as the reference point. Not a Roomba! More like what you find in outer space. Absolute pressure measurement has the advantage of the reference staying the same no matter the altitude or weather, a big plus in some processes.

4 – What is differential pressure measurement

As I said in the last section, if you need pressure measurement to get the difference in pressure between two points, then you need a DP transmitter. Also, you can use it to measure flow and level in a vast range of applications, and many companies and users do.

DP transmitters have ruled process measurement for a long time and still appear in new applications. However, today you can find other solutions to measure flow and level, and some of them provide more pros than cons compared to DP transmitters. Maybe one day one of these solutions will unseat DP from its industrial throne.

5 – What is static pressure measurement

Static pressure measurement refers to reading the force exerted by a fluid in all directions, but usually inside a pipe or vessel. If you install a manometer on the side of a pipe, when fluid goes through you’ll measure the static pressure. Same goes for tanks and other examples.

For this pressure measurement, you can deploy a simple gauge sensor. If you want to measure the differential value, like the flow pressure on either side of an orifice plate, then you need a DP device. Yep, them again.

6 – How do you  measure level with a pressure transmitter?

Okay, this question is too broad. You can use a pressure transmitter in many ways to measure level, and the best way will depend on the process requirements.

Say you have an open tank. Then you need the high-pressure input of your transmitter at the bottom of the tank and the low-pressure input open to the atmosphere. The transmitter will measure the product based on its height and density in your tank. Now, if you have a closed vessel, then you need to connect the low-pressure input to the top of the vessel instead.

That’s just one example. To learn more, read our definitive guide on pressure transmitters.

7 – What is the difference between hydrostatic and differential pressure transmitters

These two differ by installation. For a tank, you install a DP transmitter outside, with the high-pressure input connected at the bottom and the low-pressure input open to the air.

A hydrostatic sensor goes inside the tank, and it’ll use atmospheric pressure too. You can read the details in the technical docs from the vendor, but basically, you have a guide pipe for the atmospheric pressure. This graphic will show you what I mean:

pressure measurement: hydrostatic sensor

Seven questions down, seven zillion to go and all about pressure measurement! Haha, I’m sure there aren’t THAT many. At least I hope not. Anyway, I’ll keep searching to find common questions regarding automation on Google. See you next time!

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