Meaning
Measurement techniques that determine an unknown value by comparing it to a known reference value eliminate common-mode noise and supply voltage fluctuations. A ratiometric measurement derives the output from the ratio of two voltages rather than an absolute voltage value. This technique is limited to systems where the signal source and the reference share the same excitation supply.
Design Advantage
Fluctuations in the supply voltage affect both the sensor output and the reference voltage equally, cancelling out the error in the final ratio. This self-correcting nature simplifies the design of the power supply since high-precision voltage regulators are no longer necessary. It reduces both the component count and the overall power consumption of the circuit, which is highly beneficial for battery-powered instruments.
Reference Selection
The choice of reference resistor or voltage source determines the ultimate stability and accuracy of the measurement. High-stability foil resistors are commonly used in oceanographic sensor bridges to act as the reference. Their resistance must remain constant across the entire operating temperature range to prevent scale-factor errors.
Calibration Impact
Implementing this technique reduces the frequency of recalibration because the system is immune to drift in the excitation source. This lowers the long-term maintenance costs of autonomous deep-sea deployments.
