Method for calibrating a temperature sensor of a vapour compression system
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Solution Overview
Problem
Existing methods for calibrating temperature sensors in vapor compression systems, such as refrigeration and air conditioning systems, often require flooding the evaporator, which can lead to liquid refrigerant entering the compressor and causing damage, and do not allow for accurate calibration during system operation.
Innovation Solution
A method involving alternatingly increasing and decreasing the opening degree of the expansion device in the vapor compression system to monitor and register temperature differences between refrigerant entering and leaving the evaporator, calculating a calibration value to adjust the temperature measurements of the first temperature sensor, ensuring accurate and reliable measurements without flooding the evaporator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the evaporator is flooded to calibrate temperature sensors, then calibration accuracy is improved, but liquid refrigerant may enter the suction line and reach the compressor causing damage
Solution Approach 1:
The expansion valve opening is varied periodically between maximum and minimum positions for a predetermined number of cycles. This periodic variation creates temperature oscillations that allow calibration without sustained flooding, eliminating the harmful effect of liquid refrigerant accumulation while maintaining calibration accuracy through dynamic temperature variation.
Solution Approach 2:
Instead of maintaining a static flooded state, the system dynamically adjusts the expansion valve opening during calibration. The opening is continuously varied between extremes, creating a dynamic calibration process that prevents liquid refrigerant accumulation while still achieving accurate temperature sensor calibration through the resulting temperature oscillations.
2Measurement precision
If traditional calibration methods are used, then temperature sensor accuracy can be improved, but the calibration process requires system shutdown and cannot be performed during operation
Solution Approach 1:
The system performs calibration autonomously during normal operation without requiring external intervention or system shutdown. The control device automatically varies the expansion valve opening and processes temperature measurements to calculate calibration values, enabling the system to service itself while maintaining productivity.
Solution Approach 2:
The calibration process is integrated into continuous system operation rather than requiring periodic shutdowns. Temperature measurements are taken continuously during normal refrigeration cycles, and calibration values are calculated and applied without interrupting the useful cooling action, ensuring continuous productivity.
3Reliability
If the expansion device opening is varied dynamically during calibration, then calibration can be performed without flooding the evaporator, but the control complexity increases
Solution Approach 1:
The calibration process is segmented into discrete cycles with a predetermined number of oscillations. Each cycle consists of systematic opening variations between maximum and minimum positions, breaking down the complex calibration task into manageable, repeatable segments that simplify control while ensuring reliability.
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 method allows for easy and accurate calibration of temperature sensors in vapor compression systems, ensuring reliable superheat value measurements and preventing compressor damage by avoiding liquid refrigerant entry, while maintaining system operation.
Implementation Method 1
an expansion device having a variable opening degree... alternatingly increasing and decreasing the opening degree of the expansion device
Implementation Method 2
a first temperature sensor, S1, arranged in the refrigerant path at an inlet opening of the evaporator, and a second temperature sensor, S2, arranged in the refrigerant path at an outlet opening of the evaporator
Data Source
AI summary
A method for calibrating a temperature sensor arranged in a vapor compression system is disclosed. The opening degree of an expansion device is alternatingly increased and decreased. Simultaneously a temperature of refrigerant entering the evaporator and a temperature of refrigerant leaving the evaporator are monitored. For each cycle of the opening degree of the expansion device, a maximum temperature, T1, max, of refrigerant entering the evaporator, and a minimum temperature, T2, min, of refrigerant leaving the evaporator are registered. A calibration value, ΔT1, is calculated as ΔT1=C−(T2, min−T1, max) for each cycle, and a maximum calibration value, among the calculated values is selected. Finally, temperature measurements performed by the first temperature sensor are adjusted by an amount defined by ΔT1, max.