Multiplexer Equalizer Circuit for Sensor Voltage Matching
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Solution Overview
Problem
Field-mounted process devices face challenges such as voltage potential differences between sensors, which can introduce measurement errors and damage circuitry when using multiplexers to couple multiple sensors to a single transmitter, especially in two-wire process control systems with limited power.
Innovation Solution
Incorporating an equalization circuit that momentarily connects the multiplexor bus to a circuit voltage reference to equalize the voltage potential between sensors and signal conversion circuitry, ensuring accurate measurements by bringing all components to a common voltage before taking readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple sensors are coupled to a single transmitter using a multiplexer, then the number of transmitters is reduced and wiring costs are reduced, but voltage potential differences between sensors introduce measurement errors and can damage circuitry
Solution Approach 1:
The equalizer circuit performs preliminary voltage equalization before the multiplexer switches between sensors. By pre-charging or discharging the measurement bus to match the voltage potential of the next sensor to be measured, the circuit eliminates voltage transients and potential differences that would otherwise cause measurement errors or damage circuitry.
Solution Approach 2:
The equalizer circuit acts as an intermediary between the multiplexer and the sensors. It mediates the voltage potential differences by providing a buffering mechanism that equalizes voltages before signals are transferred to the measurement bus, thereby protecting the circuitry and ensuring accurate measurements.
2Loss of substance
If multiple sensors are coupled to a single transmitter using a multiplexer, then wiring costs are reduced, but residual voltages from previous measurements cause errors in current measurements
Solution Approach 1:
Before each sensor measurement, the equalizer circuit performs preliminary voltage equalization by charging or discharging the measurement bus to match the voltage potential of the sensor to be measured. This preliminary action eliminates residual voltages from previous measurements that would otherwise contaminate current measurements.
3Reliability
If field-mounted devices use robust enclosures and electrical isolation techniques to withstand environmental conditions, then device reliability is improved, but device complexity increases
Solution Approach 1:
The equalizer circuit is integrated into the existing transmitter architecture, merging the voltage equalization function with the multiplexer and measurement circuitry. This integration approach improves measurement reliability while minimizing the increase in device complexity by sharing existing components and circuit paths.
Data Source
AI summary
An industrial process control transmitter includes a first input configured to couple to a first sensor, and a second input configured to couple to a second sensor. Measurement circuitry is configured to couple to the first and second sensors and provide an output related to a sensed process variable. A multiplexer is configured to selectively couple the first and second sensors to the measurement circuitry. An equalizer circuit is coupled to the first and second sensors and configured to equalize a voltage potential between the first sensor and the measurement circuitry.