Removable PCB Terminal Block for Accurate Cold Junction Compensation
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Solution Overview
Problem
Accurate cold junction compensation in thermocouples is challenging due to difficulties in measuring the temperature at the cold junction, which is often subject to size and space constraints, leading to measurement errors of 1.5 to 2 degrees.
Innovation Solution
A terminal block with a removable PCB and internal thermocouples having legs made of different materials, coupled with a processing circuit to measure and compensate for the cold junction temperature, providing precise temperature readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a temperature sensor is closely coupled to the wire termination on the field terminal for cold junction temperature measurement, then measurement accuracy is improved, but space constraints and size limitations worsen
Solution Approach 1:
An internal thermocouple is introduced as an intermediary element within the connector assembly. This internal thermocouple measures the temperature at the wire termination point (cold junction) directly, serving as a mediator between the limited space in the field terminal and the need for accurate temperature measurement. The internal thermocouple's junction is positioned at the terminal block where field wires connect, allowing accurate cold junction temperature sensing without requiring additional external space.
2Measurement precision
If the cold junction temperature is measured accurately at the wire termination, then cold junction compensation precision is improved, but device complexity worsens
Solution Approach 1:
The internal thermocouple is merged with the connector assembly structure itself. The thermocouple legs are integrated into the terminal block, with one leg connected to the field wire terminal and the other leg connected to the PCB. This merging of the temperature sensing function into the existing connector structure achieves accurate cold junction compensation without adding separate, complex external components.
Solution Approach 2:
The internal thermocouple serves multiple functions: it provides cold junction temperature measurement for compensation, and its structure is universal across different connector assemblies. The same internal thermocouple design can be used in various terminal block configurations, making the solution broadly applicable without increasing overall system complexity.
3Reliability
If ambient thermal influences are eliminated through proper sensor placement, then measurement reliability is improved, but ease of operation worsens
Solution Approach 1:
The system is segmented into modular components: the terminal block with integrated internal thermocouple, the PCB with temperature sensor, and the removable connector assembly. This segmentation allows the internal thermocouple to be permanently installed in the terminal block where it is protected from ambient thermal influences, while the PCB can be easily installed or removed without affecting the reliability of the temperature measurement. The modular design maintains measurement reliability while preserving ease of operation.
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
The solution achieves accurate cold junction compensation with reduced measurement errors, instant accuracy, and independence from ambient thermal influences, allowing for precise hot junction temperature measurements.
Implementation Method 1
The internal thermocouple has two conductive legs which are formed of different materials and are separated at an end to form a jaw connector... The processing circuit can be configured to determine a temperature differential between the terminal block and the printed circuit board according to voltage difference between the two legs of the internal thermocouple
Implementation Method 2
The thermocouple includes two electrical wires which are made of two different types of conductive metals and joined together to form two junctions... The temperature difference causes a voltage to develop between the wire pair that is approximately proportional to the difference between the temperatures of the two junctions
Data Source
AI summary
An input module includes a terminal block defining a plurality of terminals. Each terminal includes an opening to receive an external wire. The electrical connector assembly is received by at least one terminal and includes an internal thermocouple and a pivot member. The internal thermocouple has a first leg and a second leg coupled together at a first end of the internal thermocouple and spaced apart to define a jaw connector at a second end. The pivot member is pivotable to couple the external wire to the first end. The input module includes a printed circuit board to be coupled to the electrical connector assembly via the jaw connector. The printed circuit board includes a processing circuit to perform cold junction compensation based on a temperature of the printed circuit board and a temperature or a voltage of the internal thermocouple.