Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Pneumatic Moment-balance Differential Pressure Transmitter
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Practical Questions > Pneumatic Moment-balance Differential Pressure Transmitter

Pneumatic Moment-balance Differential Pressure Transmitter

Explain the principle of Pneumatic Moment-balance Differential Pressure Transmitter using the circuit diagram.

Last updated: October 3, 2020 10:04 am
Editorial Staff
Practical Questions
No Comments
Share
3 Min Read
SHARE

The following diagram is that of a pneumatic moment-balance differential pressure transmitter, similar to the Foxboro model 13A. The term “moment” refers to the physics principle of a force acting on a lever to produce a torque.

“Moment-balance” is more appropriate than “force-balance” in this case because the device pits moment against moment, rather than force against force directly:

Pneumatic Differential Pressure Transmitter

Pneumatic Moment-balance Differential Pressure Transmitter

Describe this instrument’s response to an increasing differential pressure (increasing pressure on the “High” side, and steady pressure on the “Low” side; or decreasing pressure on the “Low” side with steady pressure on the “High” side), step by step.

Answer:

As the differential pressure increases (“high” side pressure increases relative to “low” side pressure):

  • The diaphragm “capsule” is forced to the right.
  • The Force bar rotates counter-clockwise about the sealing diaphragm, which acts as a fulcrum for the force bar.
  • Flapper approaches nozzle.
  • Nozzle backpressure increases.
  • Increased nozzle backpressure presses up on relay diaphragm.
  • Inside the relay, the ball-shaped supply valve opens and the cone-shaped vent valve closes.
  • Relay output pressure increases (more than the nozzle backpressure increase, due to amplification).
  • This output pressure is sent to the bellows, which presses to the left at the range bar’s lower end.
  • The range bar rotates clockwise about the “range wheel” (movable fulcrum nut).
  • The top of range bar moves to the right, pulling against the force bar to move the flapper away from the nozzle.
  • The system reaches equilibrium, where the force exerted by the bellows against the range bar balances force exerted by the diaphragm capsule against the force bar.

End result: output pressure equals some proportion (multiple or fraction) of differential pressure across the diaphragm capsule.

More Questions

1. Describe the purpose of the sealing diaphragm shown roughly mid-way along the length of the force bar.

2. Identify how this instrument will respond to obstructions (blockages) in the following locations:

→ Orifice

→ Nozzle

→ Vent (located on relay body)

Interest to add any further points? Share your answers with us through the below comments section.

Read Next:

  • Pressure Gauge Dial
  • Level Gauge Design
  • Diaphragm Pressure Sensor
  • Pneumatic Relay Questions
  • Instrument Calibration Question

Credits: Tony R. Kuphaldt

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

Air Pressure Inside the Tank
Air Compressor Control Circuit Problem
Practical Process Control System Questions & Answers – 3
Liquid Flow Control Loop Controller Action
Questions on Pneumatic Transmitter and Repeater
Displacer Type Density Transmitter Question
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

Is it Possible to Measure Liquid-Liquid Level Interface using Float?
Type E thermocouple Calculations
PLC Practice Questions
Identify Solenoid Valves Energized or de-energized?
Programmable Logic Controller (PLC) Questions and Answers – 8
Purpose of Stop in a Pressure Measuring Instrument
Determine the Problems with Level Transmitter and Gauge
Compressor Emergency Shutdown Root Cause Analysis

Keep Learning

Problem on Tachogenerator

Problem on Tachogenerator

process conditions, Find out the Circuit Components Status

As per Process Conditions, Find out the Circuit Components Status ?

Span of Pressure Gauge

How to Decrease Span of Pressure Gauge?

Programmable Logic Controller (PLC) Questions and Answers

Programmable Logic Controller (PLC) Questions and Answers – 2

Identify which lamp in the following ladder-logic diagram

Identify High Flow Alarm and Low Flow Alarm?

Inclined Water Manometer

How much Pressure is applied to Inclined Water Manometer?

Instrument Switch Status

Define Normal Status of a Process Switch ?

Differential Capacitance Pressure Sensor Circuit

Differential Capacitance Pressure Sensor Circuit

Learn More

Difference Between Circuit Breaker and Fuse

Difference Between Circuit Breaker and Fuse

Infrared Flue Gas Analyser

What is Infrared Flue Gas Analyzer? – Working Principle

Pressure Switch Construction

Basics of Pressure switches

Transistor Collector Characteristic Curves

Transistor Collector Characteristic Curves

Purpose of Isolation valve

What are Isolation valves? – Purpose, Types, Configurations

Orifice Plate

Orifice Plate Questions and Answers

Protection Relays Interview Questions & Answers

Protection Relays Interview Questions & Answers

Error sources creating Uncertainty in calibration

Error sources creating uncertainty in Calibration

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?