Galvanic Isolation for pH Probe Impedance Measurement
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Solution Overview
Problem
Existing measuring systems for process materials, such as pH and oxygen probes, face accuracy issues due to leakage currents between the signal and stimulation circuits, especially when measuring weak signals, and cannot directly determine the impedance of the glass electrode.
Innovation Solution
A measuring system with a galvanically isolated test signal circuit and measurement signal circuit, using a transformer as a coupling element to prevent leakage currents, allowing for direct determination of the glass electrode's impedance and improved measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a test signal circuit is coupled to the measurement signal circuit to determine electrical characteristics, then measurement precision is improved, but leakage currents adversely affect accuracy
Solution Approach 1:
A coupling element is introduced as an intermediary between the test signal circuit and measurement signal circuit. This coupling element enables signal transfer for impedance determination while preventing direct electrical connection that causes leakage currents, thus resolving the contradiction between measurement capability and measurement accuracy.
2Measurement precision
If the measuring probe is used to measure weak signals, then measurement sensitivity is improved, but leakage currents have a more significant adverse effect on accuracy
Solution Approach 1:
The coupling element serves as a mediator that allows the test signal to influence the measurement signal circuit without creating direct leakage current paths. This is particularly beneficial for weak signal measurements where even small leakage currents would significantly degrade measurement accuracy.
3Measurement precision
If the signal measuring circuit is coupled to the stimulation circuit for resistance determination, then electrical characteristic measurement is enabled, but the measuring signal is still influenced by the stimulation circuit
Solution Approach 1:
The coupling element enables the test signal circuit to determine the impedance of the glass electrode while preventing the stimulation circuit from directly influencing the measurement signal. The coupling element transfers the necessary signal information while blocking harmful electrical influence from the stimulation circuit.
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 ensures accurate determination of electrical characteristics of the sensing element, reducing measurement errors and enabling quicker characterization of the glass electrode's impedance, even with high pH-glass resistance, thus enhancing measurement precision and efficiency.
Implementation Method 1
a transformer as a coupling element to prevent leakage currents
Data Source
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AI summary
The present disclosure relates to means for monitoring and/or determining the condition of a measuring probe adapted to measure at least one property of a process material - such as a pH measurement, a CO2 or an oxygen concentration, comprising: • an electrode provided with a sensing element arranged so as to deliver a measurement signal into a measurement signal circuit, the electrode voltage being related to at least one property of the process material when the electrode is in contact with the process material; • a signal-processing unit adapted to determine a measurement quantity related to the at least one property of the process material during operation of the measuring probe according to the measurement signal; • a signal source configured to deliver, during a verification phase, a test signal (SIG) into a test signal circuit; • a coupling element arranged to ensure galvanic isolation between the measurement signal circuit and the test signal circuit.