Figure 8 Bridge Circuit

Temperature Detectors TEMPERATURE DETECTION CIRCUITRY Figure 8 Bridge Circuit Resistors R₁ and R₂ are the ratio arms of the bridge. They ratio the two variable resistances for current flow through the ammeter. R₃ is a variable resistor known as the standard arm that is adjusted to match the unknown resistor. The sensing ammeter visually displays the current that is flowing through the bridge circuit. Analysis of the circuit shows that when R₃ is adjusted so that the ammeter reads zero current, the resistance of both arms of the bridge circuit is the same. Equation 1-1 shows the relationship of the resistance between the two arms of the bridge. (1-1) R₁ R₃ R₂ R_x Since the values of R₁, R₂, and R₃ are known values, the only unkown is R_x. The value of R_x can be calulated for the bridge during an ammeter zero current condition. Knowing this resistance value provides a baseline point for calibration of the instrument attached to the bridge circuit. The unknown resistance, R_x, is given by Equation 1-2. (1-2) R_x R₂R₃ R₁ Rev. 0 Page 11 IC-01