Measuring Instrument Digital Signal Processing for Conductivity
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Solution Overview
Problem
Existing measuring instruments using alternating current signals face challenges in accurately following changes in physical amounts due to signal saturation and noise, particularly when the electrical conductivity of the sample liquid is extreme, and struggle with gain switching, leading to output abnormalities and insufficient detection of rapid changes.
Innovation Solution
The proposed measuring instrument includes a sensor unit, a reference signal output unit, a multiplication unit, an A/D conversion unit, and an integration unit, which allows for digital signal processing and integration over a predetermined time, enabling faster response to changes in physical amounts. Additionally, upstream and downstream amplifiers are used to manage signal saturation and noise, and a memory unit is included to prevent output spikes during gain switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lowpass filter with a large time constant is used to eliminate ripple, then the ripple of the alternating current component is sufficiently eliminated, but the signal generated according to a change in the sensor unit is delayed
Solution Approach 1:
The patent replaces the analog lowpass filter (mechanical/electrical filtering system) with a digital signal processing system. The multiplication unit multiplies the sensor output by a reference signal to generate a cosine wave, and the integration unit integrates this cosine wave over one cycle to extract the direct current component. This substitution eliminates the need for a large time constant filter, thereby removing the signal delay while still achieving effective ripple elimination through mathematical integration.
2Measurement precision
If the gain of the amplifier is adjusted by changing the value of the variable resistor, then the output signal falls within a suitable range, but an abnormality (spike) occurs in the output signal during gain switching
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the integration results of the cosine wave in a memory unit before gain switching occurs. When gain switching is needed, the system switches between pre-computed integration results rather than performing integration during the transition. This ensures that the output signal remains stable and free from spikes, as the switching occurs at discrete, pre-prepared states rather than during continuous signal processing.
3Quantity of substance
If the electrical conductivity of the sample liquid is extremely large, then the current flowing between both electrodes extremely increases, but the subsequent circuit does not correspond to such an excessive signal, causing saturation
Solution Approach 1:
The patent applies dynamics by making the gain of the amplifier adjustable through variable resistors (14 and 19). When the electrical conductivity of the sample liquid is extremely large, the system increases the attenuation (decreases gain) to prevent saturation. When conductivity is extremely small, the system increases the gain to amplify weak signals above noise levels. This dynamic adjustment allows the circuit to handle a wide range of conductivity values reliably without saturation or noise dominance.
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 configuration allows for accurate and swift measurement of physical amounts with minimal delay, effectively addressing the limitations of existing technologies by preventing signal saturation and noise issues, and enabling precise detection of rapid changes in electrical conductivity.
Implementation Method 1
measures a current flowing between both electrodes, and thus, calculates an electrical conductivity of the eluate flowing between both electrodes
Implementation Method 2
The output signal of the sensor unit 12 is multiplied by a reference signal (a sine curve) having the same frequency and phase as those of the alternating current source 11, in a multiplication unit 16
Implementation Method 3
an integration unit integrating a digital signal which is output of the multiplication unit, for a predetermined time
Data Source
AI summary
A measuring instrument including: a sensor unit outputting an alternating current signal having an amplitude corresponding to a physical amount of a measurement target; a reference signal output unit outputting a reference signal having the same frequency and the same phase as those of the alternating current signal; a multiplication unit multiplying the alternating current signal and the reference signal together; an A/D conversion unit disposed before or after the multiplication unit; and an integration unit integrating a digital signal which is output of the multiplication unit, for a predetermined time. It is possible to measure a value of the physical amount of the measurement target only with a delay of one cycle of the alternating current signal.