RTD Degradation Detection via Diagnostic Excitation
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Solution Overview
Problem
High-temperature resistance temperature devices (RTDs) experience errors due to changes in insulative materials becoming conductive, leading to undetectable measurement errors, especially at temperatures above 600°C, where energy storage characteristics complicate accurate temperature measurement.
Innovation Solution
A process fluid temperature transmitter with a controller that applies an excitation signal to the RTD, measures its response, and performs diagnostics to detect and compensate for energy storage effects, adjusting the settling time to ensure accurate measurements by taking multiple voltage measurements after the excitation current is removed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If RTDs are used at higher temperatures, then temperature measurement capability is improved, but measurement accuracy deteriorates due to energy storage effects and insulative material degradation
Solution Approach 1:
The system performs a diagnostic measurement before the main temperature measurement to detect energy storage effects. By measuring the RTD response immediately after applying excitation current, the system identifies abnormal capacitance effects before they corrupt the primary measurement, allowing for compensatory actions to be taken.
Solution Approach 2:
The system uses the diagnostic measurement results to adjust subsequent measurements. When energy storage effects are detected through the preliminary diagnostic, the system modifies the measurement sequence or parameters to compensate for the identified issues, ensuring accurate temperature readings despite high-temperature conditions.
2Speed
If standard measurement procedures are used, then measurement speed is maintained, but measurement accuracy deteriorates due to undetectable energy storage effects
Solution Approach 1:
A quick diagnostic measurement is performed before the main measurement to detect energy storage effects. This preliminary check identifies problematic RTD conditions without significantly delaying the overall measurement process, maintaining measurement speed while enabling accuracy corrections.
Solution Approach 2:
The system changes measurement parameters dynamically based on diagnostic results. When energy storage effects are detected, the system adjusts excitation current levels, measurement timing, or settling periods to compensate for the abnormal RTD behavior, maintaining both speed and accuracy.
3Measurement precision
If diagnostic measurements are added to detect energy storage effects, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The existing RTD measurement circuitry is used for multiple purposes: both standard temperature measurement and diagnostic detection of energy storage effects. The same excitation source and measurement device perform both functions, avoiding the need for separate dedicated diagnostic hardware and minimizing device complexity.
Solution Approach 2:
The RTD itself provides information about its own condition through its electrical characteristics. By measuring the RTD's response to excitation current, the system self-diagnoses energy storage effects without requiring external test equipment or additional sensors, keeping the system simple while improving accuracy.
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 effectively reduces measurement errors caused by energy storage in RTDs at high temperatures, maintaining accurate temperature readings and providing indications for maintenance, thus enhancing precision and safety in process control.
Implementation Method 1
An RTD changes its resistance in response to change in temperature. By measuring the resistance of an RTD, temperature can be calculated.
Implementation Method 2
Such resistance measurement is generally accomplished by passing a known current through the RTD, and measuring the associated voltage developed across the RTD.
Implementation Method 3
As RTDs are required to be used in applications at higher and higher temperatures, additional sources of error can cause errors in the output of such RTDs. As process fluid temperature measurement has become more accurate, there is in increasing need to identify and compensate for smaller and smaller sources of error such as those that can develop in high-temperature applications.
Data Source
AI summary
A process fluid temperature transmitter includes a plurality of terminals, an excitation source, a measurement device, and a controller. The plurality of terminals is couplable to an RTD. The excitation source is operably coupled to the plurality of terminals and is configured to apply an excitation signal to the RTD. The measurement device is coupled to the plurality of terminals and is configured to measure a response of the RTD to the applied excitation signal. The controller is coupled to the excitation source and the measurement device. The controller is configured to perform an RTD resistance measurement by causing the excitation source to apply the excitation signal to the RTD and to cause the measurement device to measure the response of the RTD while the excitation signal is applied to the RTD. The controller is also configured to perform an RTD diagnostic by causing the excitation source to change application of the excitation signal and causing the measurement device to measure an RTD response to the changed excitation signal.