# ISA Interchange

Welcome to the official blog of the International Society of Automation (ISA).

This blog covers numerous topics on industrial automation such as operations & management, continuous & batch processing, connectivity, manufacturing & machine control, and Industry 4.0.

The material and information contained on this website is for general information purposes only. ISA blog posts may be authored by ISA staff and guest authors from the automation community. Views and opinions expressed by a guest author are solely their own, and do not necessarily represent those of ISA. Posts made by guest authors have been subject to peer review.

# AutoQuiz: How Do You Calculate the Pressure Measurement of an Open Tube Manometer

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AutoQuiz is edited by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for more information about the CCST program.

### If an open tube manometer indicates 6.11 inches of Hg (mercury), what is the pressure measurement?

A) 2 psi
B) 3 psia
C) 17.89 psig
D) 3 psig
E) none of the above

First, recall the arrangement that constitutes an open tube manometer.

Now, recall the definitions and nomenclature of pressure.

Pabsolute = Pgauge + Patmospheric which is often noted as Pa = Pg + Patm or psia = psig + Patm.

Looking at the diagram of an open tube manometer one can see that what one is looking for to answer this question is the value for h (P2) or psig.

The next chore is to convert the units of inches of mercury to pounds per square inch (psi).

Use a conversion of 29.921 inches of Hg at 0°C to 14.696 lbf/in2 at 0°C to get 3 psig, which is answer D, the correct answer.

Be careful not to choose answer C, which is a pretty good answer for the absolute pressure (psia) but not for the gauge pressure (psig). Answer B is the correct numerical answer for the wrong parameter (psia).

Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

Connect with Joel

###### Joel Don
Joel Don is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.