Flow Calibration Using Valve Position and Chamber Volume Compensation

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Solution Overview

Problem

Accurate calibration and validation of small-scale mass flow controllers, especially those with small chamber volumes, are challenging due to small variations in the position of the control valve affecting downstream chamber volume, which complicates precise measurement and control of low flow rates.

Innovation Solution

A rate-of-change flow measurement device with a block body, position control valve, pressure sensors, and a processor that calculates chamber volume by measuring valve position and pressure changes, allowing for precise calibration and validation by maintaining a constant pressure set point during calibration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the control valve position varies, then the mass flow controller can adjust flow rates, but the downstream chamber volume changes, complicating accurate measurement

Engineering Contradiction:

Improveflow rate adjustment capabilityVSAvoidcalibration and validation complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The system performs preliminary calibration by moving the control valve to a series of known positions and measuring the corresponding chamber volumes using the correlation between upstream pressure, downstream pressure, and valve position. This pre-established volume lookup table compensates for volume variations during actual flow measurements, resolving the precision issue.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors upstream and downstream pressures along with valve position feedback to dynamically determine chamber volume during operation. This real-time feedback mechanism allows the system to adapt to valve position changes and maintain measurement accuracy without manual recalibration.

Inventive Principle:

Principle #23Feedback

2Reliability

If traditional mass flow control calibration methods are used, then the calibration process can be performed, but small variations in valve position and chamber volume require repeated adjustments, increasing calibration time

Engineering Contradiction:

Improvecalibration accuracyVSAvoidcalibration time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent replaces direct mechanical measurement of chamber volume with a computational approach using pressure sensors and a lookup table. Instead of mechanically measuring volume changes, the system uses pressure differential measurements combined with pre-stored correlation data to determine volume, eliminating mechanical measurement errors.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

Enables accurate and repeatable measurement of small flow rates by compensating for chamber volume variations, ensuring precise control and measurement of fluid flow, even at low flow rates.

Implementation Method 1

a first pressure sensor located on a first side of the flow path from the position control valve and configured to detect a first pressure at the first side of the flow path

Methodology Applied

Scientific EffectPressure detection:

Implementation Method 2

a second pressure sensor located on a second side of the flow path from the position control valve and configured to detect a second pressure at the second side of the flow path adjacent the chamber

Methodology Applied

Scientific EffectPressure detection:

Implementation Method 3

a valve position sensor configured to measure a valve position of the actuator of the position control valve

Methodology Applied

Scientific EffectPosition detection:

Implementation Method 4

calculate a volume of the chamber at least in part using the valve position data when a calibration of a device-under-test is performed by decreasing a pressure of the chamber or increasing the pressure of the chamber while opening the position control valve to maintain the first pressure constant to stay at a pressure set point

Methodology Applied

Scientific EffectPressure-volume relationship calculation:

Data Source

PatentUS11860018B2Rate-of-change flow measurement device

Publication Date: 2024.01.02 HORIBA STEC CO LTD

AI summary

A rate-of-change flow measurement device is provided including first pressure sensor, a position control valve with a valve position sensor, a second sensor position and a chamber comprising a part of the flow path of the device, and an isolation valve, arranged in this order along the flow path of the device. The device receives valve position data from the valve position sensor and pressure data from the pressure sensors, and calculates a volume of the chamber at least in part using the valve position data when a calibration of a device-under-test is performed by decreasing a pressure of the chamber or increasing the pressure of the chamber while opening the position control valve to maintain the pressure reading of the first pressure sensor constant to stay at a pressure set point.