Network Impedance
Electrical networks consisting of four resistive arms allow for the precise measurement of small changes in impedance by detecting the balance of voltage between two parallel branches. This wheatstone bridge resistance configuration is the standard method for extracting signals from strain-based sensors. It converts a change in the resistance of one or more arms into a measurable output voltage.
The circuit is at its most sensitive when all four arms have identical values.
Voltage Balance
When no pressure is applied, the voltage across the output terminals should be zero. In a system measuring wheatstone bridge resistance, any deviation from this balance is interpreted as a signal. Small trim resistors are often added to correct for initial manufacturing tolerances.
Current Flow
Power consumption is a primary consideration for battery-operated transmitters. Increasing the wheatstone bridge resistance reduces the current draw but can increase the vulnerability to electrical noise. Designers must find the optimal value for the specific application.
Precision Measurement
High resolution analog-to-digital converters translate the small millivolt signal into a digital value. Because wheatstone bridge resistance is sensitive to temperature, compensating for thermal effects is a major part of sensor calibration. The stability of the bridge determines the long term accuracy of the instrument.
