Process Automation Display With Analog-Digital Signal Comparison
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Solution Overview
Problem
Analog coding of output data in industrial process automation is prone to inaccuracies due to production tolerances and external disturbances, leading to deviations in signal transmission that can be intolerable for field devices.
Innovation Solution
A display device with a controller that requests and receives digitally coded signals via a fieldbus interface, compares them with analog input data, and displays the results, using light sources to indicate deviations and control relays to transmit monitoring results, while also encoding and decoding signals according to standardized formats.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog coding is used to transmit output data via current loop interface, then the field device can be powered and communicate using a single wired interface, but the transmission accuracy deteriorates due to tolerances and external disturbances
Solution Approach 1:
The controller compares the analog input data with the digitally coded output data and uses this comparison feedback to detect deviations. The system continuously monitors the analog signal against the digital reference and can trigger alerts or corrections when deviations exceed acceptable thresholds, thereby maintaining accuracy despite using analog transmission.
Solution Approach 2:
The system changes the parameter representation by transmitting the same data in two different formats: analog coded signal for power-efficient single-wire communication and digital coded signal for accurate reference comparison. This dual-parameter approach allows the system to leverage the benefits of both analog (simplicity, power efficiency) and digital (precision, immunity to interference) transmission methods.
2Ease of manufacture
If analog coded signals are used for communication, then the system can operate with simple wired fieldbus infrastructure, but the deviation from original data becomes intolerable for precise applications
Solution Approach 1:
The system creates a digital copy of the output data and transmits it separately via the fieldbus interface. This digital copy serves as a reference against which the analog transmitted signal can be compared. By having both the analog signal (for compatibility) and its digital copy (for accuracy verification), the system maintains reliability while preserving ease of manufacture.
Solution Approach 2:
The fieldbus interface serves multiple functions: it transmits the digital reference data for accuracy comparison, enables controller communication, and provides a backup communication path. This multi-functionality allows the simple wired infrastructure to simultaneously support both analog power/communication and digital reference transmission, enhancing reliability without complicating the physical infrastructure.
3Measurement precision
If the controller compares analog input data with digital output data, then transmission deviations can be detected, but the device complexity increases due to additional comparison and processing functions
Solution Approach 1:
The controller performs comparison only when necessary - specifically when digital output data is available for comparison with analog input data. The system doesn't continuously compare all signals but selectively compares paired analog-digital data sets, performing just enough processing to detect deviations without unnecessary computational overhead. This partial action approach balances accuracy with manageable complexity.
Data Source
AI summary
A display device for process automation includes a display unit, a controller, a current loop interface and a fieldbus interface. The display device is designed for power supply via the current loop interface, and the controller is designed to assign an analog coded signal of an output data present at the current loop interface to a first input data and to display the first input data via the display unit. The controller is designed to request the transmission of the output data in the form of a digitally coded signal via the fieldbus interface, to receive the digitally coded signal via the fieldbus interface, to assign the digitally coded signal to a second input data, to perform a comparison between the first input data and the second input data, and to display a result of the comparison via the display unit.