Gas Valve Characterization for Heating Device Mass Flow Control
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Solution Overview
Problem
Heaters with electronic gas-air combinations face challenges in accurately controlling the mass flow of fuel gas through gas valves due to component tolerances and potential incorrect combustion signals, leading to deviations in gas flow, which can result in unsafe operation.
Innovation Solution
A method that involves detecting the opening width and volume flow through the gas valve for different stepper motor positions, comparing these with nominal values to determine a transfer function, allowing precise control of the mass flow by adjusting the stepper motor position, and storing this transfer function for future use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an offset value is set in the heating appliance prior to installation, then safe commissioning is ensured, but the actual mass flow rate information is not available to the combustion control system
Solution Approach 1:
The gas valve is characterized before installation by determining the actual mass flow rate at different stepper motor positions and storing this information in a lookup table. This preliminary characterization ensures that when the heating appliance operates, the combustion control system can access accurate mass flow rate information without real-time measurement, resolving the contradiction between ensuring safe commissioning and providing actual mass flow rate information.
2Ease of operation
If the combustion control system uses a nominal gas valve model, then control is simplified, but significant differences occur between actual and assumed mass flow rates
Solution Approach 1:
Instead of using a fixed nominal gas valve model, the system determines actual mass flow rates at multiple stepper motor positions during characterization and stores these measured values in a lookup table. This transforms the control approach from theoretical calculation to empirical data-based control, maintaining simplicity while significantly improving mass flow rate accuracy.
3Ease of manufacture
If component tolerances are accepted in gas valves, then manufacturing cost is reduced, but flow rates differ even with the same stepper motor position
Solution Approach 1:
Each gas valve performs self-characterization during manufacturing or commissioning by measuring its own actual mass flow rates at different stepper motor positions. This self-measurement approach allows component tolerances to exist in manufacturing while ensuring that each individual valve's unique characteristics are captured and stored in its lookup table, enabling precise control without requiring high manufacturing precision.
Data Source
Figure 1
Figure 2~3
AI summary
A method for characterizing a stepper motor-controlled gas valve (5) of a heating device (1) is proposed, comprising at least the following steps: a) determining the opening width and/or the volume flow rate through the gas valve (5) for different stepper motor positions MPos_akt (19), b) comparing the opening widths and/or volume flow rates determined in step a) with corresponding opening widths or volume flow rates of a nominal gas valve for the different stepper motor positions MPos_akt (19), and determining a transfer function (17) from a stepper motor position MPos_Nom (18) of the nominal gas valve to a stepper motor position MPos_akt (19) of the gas valve (5). Furthermore, a method for operating a heating device (1) with a gas valve (5) characterized according to the proposed method and a heating device (1) are proposed.