Sealed Process Variable Transmitter Calibration Without Housing Openings
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Solution Overview
Problem
Existing analog process variable transmitter systems face challenges in calibrating zero and span settings, particularly in explosive or submersible environments, due to the need for external access to potentiometers, which exposes hazardous conditions and restricts design and size constraints.
Innovation Solution
The implementation of motorized zero and span setting actuators within a hermetically sealed transmitter housing, controlled remotely by an external calibration controller, allowing electronic adjustment of potentiometers without exposing the environment to live circuits, enabling remote calibration and reducing design constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If potentiometers are accessed through openings in the transmitter housing for calibration, then ease of operation is improved, but safety is worsened due to exposure of hazardous conditions
Solution Approach 1:
The patent replaces mechanical access to potentiometers through housing openings with an electromagnetic field-based adjustment system. A calibration magnet externally coupled to the housing interacts with magnets inside the housing to rotate the potentiometer shafts without physical penetration, eliminating the need for openings while maintaining calibration capability.
Solution Approach 2:
The patent introduces a magnetic field as an intermediary between the external calibration tool and the internal potentiometers. The calibration magnet serves as a mediator that transmits rotational motion through the housing wall via magnetic coupling, allowing adjustment without direct mechanical contact or openings.
2Object-affected harmful factors
If rotary adjustment shafts are closely fitted through housing bores to provide flame path, then safety is improved, but device complexity is worsened
Solution Approach 1:
The patent replaces the mechanical rotary shaft penetration system with a magnetic coupling system. Instead of fitting shafts through bored holes with flame paths, the system uses externally applied magnetic fields to rotate internal magnets that are magnetically coupled to the potentiometer shafts, eliminating complex mechanical penetration structures.
3Ease of operation
If bar magnets are used for magnetic rotation of potentiometers, then ease of operation is improved, but manufacturing precision is worsened due to mechanical hysteresis
Solution Approach 1:
The patent employs a dynamic magnetic coupling system where the calibration magnet can be moved and repositioned externally to achieve precise control over the potentiometer adjustment. The magnetic field strength and direction can be dynamically varied to overcome hysteresis effects and achieve accurate span and zero settings.
4Ease of operation
If openings are provided in housing for switch actuation, then ease of operation is improved, but reliability is worsened due to potential leak paths
Solution Approach 1:
The patent replaces mechanical switch actuation requiring housing openings with electromagnetic actuation. Calibration magnets externally applied to the housing can magnetically actuate internal switches without requiring physical openings, thereby maintaining sealing integrity while enabling 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
This solution allows for precise and safe calibration of process variable transmitters, enhancing reliability, reducing size constraints, and improving robustness against vibrations and seismic activity, while maintaining a fully enclosed and submersible design.
Implementation Method 1
a relatively large bar magnet which is then rotated magnetically by another bar magnet outside the live circuit's enclosure
Data Source
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AI summary
A process variable transmitter (102) for measuring a process variable includes a process variable sensor (140) configured to sense a process variable and provide a sensor output. Measurement circuitry (142) receives the sensor output and provides a measured output related to the process variable. Output circuitry (150) provides a device output on a two- wire process control loop (108) based upon the measured output. The output circuitry has a transfer function that is a function of an adjustable analog circuit component (190, 192). A motorized actuator (160, 162) is configured to adjust the adjustable analog circuit component (190, 192) to thereby change the transfer function of the output circuitry. An optional calibration controller (120) is also provided.