Auto Detecting Cold Junction Compensation in I/O Modules
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Solution Overview
Problem
Existing temperature I/O modules for industrial control systems face challenges due to the need for cold junction compensation (CJC) sensors, which reduce the number of terminals available for external connections and increase manufacturing and installation costs.
Innovation Solution
The proposed solution involves integrating a CJC sensor within the I/O module base, allowing for automatic detection and eliminating the need for contact pairs between the removable terminal block (RTB) and the base, thus preserving terminal availability and simplifying manufacturing and installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CJC sensor is connected externally to the terminals of the RTB or embedded within the RTB, then cold junction compensation is achieved, but the number of terminals available for other I/O connections is reduced
Solution Approach 1:
The CJC sensor is extracted from the RTB and relocated to the I/O module base, separating the CJC sensing function from the terminal block. This allows the RTB to maintain all its terminals for external connections while the base provides dedicated CJC sensing capability through the internally mounted sensor.
2Measurement precision
If an RTB with embedded CJC sensors is specially manufactured, then accurate cold junction compensation is provided, but manufacturing and distribution costs increase
Solution Approach 1:
The CJC sensor functionality is extracted from the RTB and placed in the base, allowing standard RTBs to be manufactured without special modifications. The base is manufactured with integrated CJC sensors, enabling accurate compensation without requiring costly specially manufactured RTBs.
Solution Approach 2:
The system is segmented into two functional parts: the RTB handles terminal connections using standard manufacturing, while the base provides CJC sensing and processing. This division allows each component to be optimized independently, reducing overall manufacturing costs.
3Reliability
If an external CJC sensor is connected to the RTB, then cold junction compensation is achieved, but the complexity of supply and installation increases
Solution Approach 1:
The CJC sensor is merged with the I/O module base, creating an integrated unit that provides both terminal connectivity and cold junction compensation. This eliminates the need for separate external CJC sensors and their associated wiring, simplifying both supply and installation.
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 enables the I/O module to maintain full terminal availability for external connections while providing accurate cold junction compensation, reducing manufacturing and installation costs, and enhancing flexibility by allowing the module to accommodate either internal or embedded CJC sensors.
Implementation Method 1
A first cold junction compensation (CJC) sensor is mounted within the base proximate the second contact from one of the contact pairs and is operative to generate a first feedback signal corresponding to a temperature present at the second contact
Implementation Method 2
A switch is connected between the first CJC sensor and an electrical ground connection to selectively connect the first CJC sensor to the electrical ground connection
Data Source
AI summary
An I/O module configured to automatically detect a cold junction compensation (CJC) sensor includes a base and a removable terminal block (RTB). The RTB includes multiple terminals. An I/O circuit mounted within the base includes multiple contact pairs, where a first contact is mounted in the RTB and electrically connected to one of the terminals and a second contact is mounted in the base and electrically connected to the I/O circuit. A CJC sensor is mounted within the base proximate one of the second contacts and is operative to generate a feedback signal corresponding to a temperature present at the second contact. A controller in the I/O circuit generates a control signal to selectively connect the CJC sensor to an electrical ground connection. A switch connected between the CJC sensor and the electrical ground connection receives the control signal to selectively connect the CJC sensor to the electrical ground connection.