Self-Calibrating HVACR Input Circuit for Measurement Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
HVACR controllers require frequent factory calibration, which is impractical and prone to drift due to temperature and supply voltage changes, leading to inaccurate measurements over time.
Innovation Solution
A self-calibrating input circuit that includes an ADC, microprocessor, and voltage-controlled current source, allowing for periodic self-calibration and operation in multiple modes (voltage, current, resistance) without external calibration, maintaining accuracy by tracking supply voltage and using internal references.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If factory calibration is performed frequently to maintain measurement accuracy, then measurement precision is improved, but device complexity and operational burden increase
Solution Approach 1:
The system performs self-calibration automatically without requiring external calibration equipment or manual intervention. The microprocessor controls internal switches to connect known reference resistors to the ADC input, executes calibration algorithms, and stores calibration data in non-volatile memory, enabling the device to calibrate itself periodically
Solution Approach 2:
The calibration process is performed in advance during system initialization or at predetermined intervals before actual measurements are taken. The microprocessor executes calibration routines that establish baseline values and compensation factors that are stored for use during normal operation, ensuring accuracy is maintained before drift occurs
2Measurement precision
If external calibration equipment is used to maintain accuracy, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The system performs self-calibration automatically without requiring external calibration equipment or manual intervention. The microprocessor controls internal switches to connect known reference resistors to the ADC input, executes calibration algorithms, and stores calibration data in non-volatile memory, enabling the device to calibrate itself periodically
Solution Approach 2:
The input circuit is designed to accept multiple types of devices (temperature sensors, pressure sensors, flow meters) through a universal calibration interface. The same self-calibration mechanism works for different device types by switching between different reference resistors and measurement configurations
3Measurement precision
If calibration is performed at the customer site, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The system performs self-calibration automatically without requiring external calibration equipment or manual intervention. The microprocessor controls internal switches to connect known reference resistors to the ADC input, executes calibration algorithms, and stores calibration data in non-volatile memory, enabling the device to calibrate itself periodically
Solution Approach 2:
The calibration process is performed periodically at predetermined intervals or when drift thresholds are exceeded, rather than requiring continuous manual calibration. The microprocessor automatically initiates calibration sequences that complete in minimal time and store results for ongoing use
4Adaptability or versatility
If the input circuit is designed for universal compatibility, then adaptability is improved, but device complexity increases
Solution Approach 1:
The input circuit is designed to accept multiple types of devices (temperature sensors, pressure sensors, flow meters) through a universal calibration interface. The same self-calibration mechanism works for different device types by switching between different reference resistors and measurement configurations
Solution Approach 2:
The circuit uses dynamic switching elements (analog switches or multiplexers) controlled by the microprocessor to reconfigure the measurement path based on the connected device type. This allows a single physical circuit to adapt its configuration rather than requiring separate hardwired circuits for each device type
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 reliable measurements in varying conditions without the need for external calibration, ensuring consistent performance even when installed at customer sites and reducing the impact of temperature and supply voltage fluctuations.
Implementation Method 1
The circuit includes a voltage-controlled current source coupled to the amplifier and converting the supply voltage to a first current configured to drive the input port
Implementation Method 2
The circuit includes an analog-to-digital converter (ADC) coupled to the input divider, generating a first digital signal based on receiving an input voltage reference, generating a second digital signal based on receiving the divided input voltage signal
Data Source
AI summary
An illustrative embodiment disclosed herein is a circuit for sensing heating, ventilation, air conditioning, and refrigeration (HVACR) equipment. The circuit includes an input port that has an input voltage signal. The circuit includes an analog-to-digital converter (ADC) generating a first digital signal based on receiving a representation of a supply voltage, generating a second digital signal based on receiving the divided input voltage signal, and outputting the first digital signal, the second digital signal, and an output voltage reference. The circuit includes an amplifier coupled to the ADC and amplifying the output voltage reference to generate a supply voltage. The circuit includes a microprocessor coupled to the ADC and configured to calculate a first ratio of the first digital signal and the supply voltage. The microprocessor is configured to determine the input voltage signal by calculating a second ratio of the second digital signal and the first ratio.