Galvanically Isolated Analog Input Digitizing by Frequency Ratio
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Solution Overview
Problem
Galvanically isolated transmission of analog signals in field devices for process instrumentation results in high accuracy loss and increased costs due to the need for microcontrollers and complex firmware to maintain communication, especially under EMC disturbances.
Innovation Solution
The circuit arrangement transmits analog signal information as frequency without loss of accuracy, omitting the microcontroller in the first electronics unit, using a transformer for simultaneous power and frequency transmission, and employing a voltage-frequency converter for ratiometric measurement, which reduces costs and computing power demands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If galvanically isolated transmission of analog signal is used, then galvanic isolation between electronics units is achieved, but accuracy loss increases significantly
Solution Approach 1:
The patent replaces direct analog signal transmission through the galvanically isolated interface with a frequency-based transmission system. A first signal at a first frequency is generated in the second electronics unit, modulated by the analog input signal level, and transmitted through the galvanically isolated interface. This substitution of direct voltage transmission with frequency-modulated signal transmission eliminates accuracy loss while maintaining galvanic isolation.
Solution Approach 2:
The patent changes the transmission parameter from direct voltage level transmission to frequency-based transmission. The analog input signal level controls the frequency of the transmitted signal, and this frequency information is then converted back to a voltage signal in the first electronics unit. This parameter transformation allows accurate signal transmission through the galvanically isolated interface without the accuracy losses inherent in direct analog transmission.
2Measurement precision
If microcontroller with firmware is used for galvanically isolated digital transmission, then transmission accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the microcontroller and complex firmware requirements from the first electronics unit. Instead of using a microcontroller in the first unit to generate and manage digital communication, the system uses a simple frequency-generating device in the second electronics unit and a frequency-to-voltage converter in the first electronics unit. This extraction eliminates the need for complex firmware development and microcontroller hardware in the first unit while maintaining accurate transmission.
Solution Approach 2:
The patent replaces expensive, complex microcontroller-based solutions with simpler, more cost-effective components. The frequency-generating device and frequency-to-voltage converter are much simpler and cheaper than a microcontroller with specialized firmware, achieving the same transmission accuracy without the associated complexity and cost.
3Reliability
If optocoupler or capacitive link is used for digital signal transmission, then galvanic isolation is maintained, but power consumption and component costs increase
Solution Approach 1:
The patent merges the functions of galvanic isolation and signal transmission into a single frequency-based system. The transformer provides both galvanic isolation and efficient power transfer while the frequency-modulated signal carries the analog input information. This merging eliminates the need for separate optocouplers or capacitive links that would increase power consumption, as the same isolated interface used for power transfer also handles signal transmission.
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 minimizes accuracy loss and costs by stabilizing frequency settings only for short measurement periods, eliminating the need for additional devices and complex firmware, while ensuring high measurement accuracy and low power consumption.
Implementation Method 1
a transformer for simultaneous power and frequency transmission
Implementation Method 2
employing a voltage-frequency converter for ratiometric measurement
Data Source
AI summary
A circuit arrangement for detecting and digitizing an analog input signal and to a field device for process instrumentation, wherein the field device comprises such a circuit arrangement which includes a first electronics unit, a second electronics unit, and an interface by which the two electronics units are galvanically separated from each other. A first signal is generated at a first frequency in the second electronics unit. A voltage frequency converter, to which the analog input signal is routed, uses a reference frequency to generate a second signal at a second frequency that corresponds to the level of the analog input signal. After the second signal has been transmitted to the second electronics unit using an optical coupler, a ratiometric measurement of the second frequency is performed in the second electronics unit dependent on the first frequency using a capture timer.