Final answer:
The maximum bridge excitation voltage is 3.6 V to limit heating effects, and the bridge output voltage for a 10 bar pressure is calculated using the change in resistance of the strain gauge in the Wheatstone bridge equation.
Step-by-step explanation:
We have been given a pressure transducer with a nominal strain gauge resistance of 120 ohms. The strain gauge forms one arm of a Wheatstone bridge, with the other three arms also having a resistance of 120 ohms each. The strain gauge has a sensitivity of 338 mohm/bar. The maximum current through the gauge is 30 mA to avoid heating effects.
Firstly, to find the maximum permissible bridge excitation voltage, we use Ohm's law: V = I * R. With I = 30 mA and R = 120 ohms, we get V = 0.03 A * 120 ohms = 3.6 V. This is the maximum permissible bridge excitation voltage to avoid heating effects.
To calculate the bridge output voltage when measuring a 10 bar pressure, we need to consider the change in resistance of the strain gauge. With a sensitivity of 338 mohm/bar, for 10 bar, the change in resistance (ΔR) is 10 bar * 338 mohm/bar = 3380 mohm or 3.38 ohms. The gauge resistance becomes 120 ohms + 3.38 ohms = 123.38 ohms. The bridge is initially in balance; therefore, with the increase in resistance due to strain, the bridge becomes unbalanced, and we calculate the voltage output using the bridge unbalance equation: ΔV = (V * ΔR) / (2 * (R + ΔR)), where V is the bridge excitation voltage, R is the initial resistance, and ΔR is the change in resistance due to applied pressure. Substituting the known values gives us ΔV = (3.6 V * 3.38 ohms) / (2 * (120 ohms + 3.38 ohms)), which yields the bridge output voltage.