Indirect Dew Point Measurement Using Capacitive Sensor and Peltier Control

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Solution Overview

Problem

Existing methods for determining the dew point of compressed air, such as the mirror method and capacitive humidity meters, face challenges with accuracy and efficiency, particularly at low relative humidity levels, where capacitive sensors exhibit high measurement errors.

Innovation Solution

A method using a capacitive sensor to measure relative humidity, with iterative temperature adjustments to maintain a constant relative humidity, allowing for accurate dew point determination through temperature measurement and psychrometric analysis, employing a Peltier element controlled by a PID controller to maintain thermal equilibrium.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a capacitive humidity meter is used to measure relative humidity, then the apparatus is simple and inexpensive, but the measurement accuracy is low and error increases at low relative humidity

Engineering Contradiction:

Improveapparatus simplicity and costVSAvoiddew point measurement accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The invention changes the operating parameter of the capacitive sensor by maintaining it at a predetermined constant relative humidity (e.g., 50% RH) through active temperature control, rather than allowing it to operate at varying low humidity levels where measurement accuracy deteriorates

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention implements a feedback control system where the capacitive sensor continuously measures relative humidity, and the measured value is fed back to a controller that adjusts the temperature of the air fraction to maintain the predetermined constant relative humidity, ensuring optimal sensor performance

Inventive Principle:

Principle #23Feedback

2Measurement precision

If the mirror method is used to determine dew point, then measurement accuracy is high, but the apparatus requires regular recalibration and has increased complexity

Engineering Contradiction:

Improvedew point measurement accuracyVSAvoidapparatus complexity and maintenance requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention uses the capacitive sensor as an intermediary measurement device that indirectly determines dew point through relative humidity measurement and temperature control, avoiding the need for direct optical observation and mirror calibration required in traditional mirror methods

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention replaces the mechanical/optical mirror system with an electrical capacitive sensing system combined with electronic temperature control, eliminating the need for visual observation and manual recalibration while maintaining measurement accuracy

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If temperature control is used to maintain constant relative humidity, then measurement accuracy improves, but energy consumption increases

Engineering Contradiction:

Improvedew point measurement accuracyVSAvoidenergy consumption for temperature control

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The invention applies temperature control only to a small fraction of the compressed air rather than the entire air stream, using a bypass arrangement where only a portion of the air is diverted through the temperature control system, thereby reducing overall energy consumption while maintaining measurement accuracy

Inventive Principle:

Principle #16Partial or excessive action

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

This approach provides accurate and economically efficient dew point measurement, minimizing errors at low relative humidity levels by setting a constant relative humidity for optimal sensor performance, ensuring precise dew point determination.

Implementation Method 1

measuring the relative humidity of the fraction using a capacitive sensor

Methodology Applied

Scientific EffectCapacitive sensing: Capacitance

Implementation Method 2

employing a Peltier element controlled by a PID controller to maintain thermal equilibrium

Methodology Applied

Scientific EffectPeltier effect: Peltier Effect

Implementation Method 3

The PID controller is configured to control the Peltier element on the basis of the measured relative humidity

Methodology Applied

Scientific EffectFeedback control: Feedback

Implementation Method 4

determining the dew point based on the temperature

Methodology Applied

Scientific EffectPsychrometric principle:

Data Source

PatentUS20240402110A1Method and apparatus for indirect determination of the dew point of compressed air

Publication Date: 2024.12.05 ATLAS COPCO AIRPOWER NV

AI summary

An apparatus for indirectly determining the dew point of compressed air at a particulate operating pressure including a capacitive sensor for measuring a relative humidity, a heating element for both heating and cooling a fraction of the compressed air, a controller for controlling the heating element based on a measured relative humidity, a temperature sensor for determining the temperature of the fraction. The controller is further configured to control the heating element such that the fraction is maintained at a predetermined constant relative humidity such that the dew point can be determined based on the temperature of the fraction.