Study the data sheet of the instrumentation amplifier INA129 and calculate the value of 'RG' that controls the gain of the INA129 in Figure 1 such that the load cell output for 0 t... Study the data sheet of the instrumentation amplifier INA129 and calculate the value of 'RG' that controls the gain of the INA129 in Figure 1 such that the load cell output for 0 to 1 lb is mapped to 0 to +V (< +9V) or -V (< -9V) of the amplifier. Read more

Steps to Solve

1. Identify the Load Cell Output The output of the load cell is specified in mV/V, which indicates how many millivolts the load cell outputs per volt of excitation at full load.

2. Determine the Output Voltage from the Load Cell Assuming the load cell provides a rating of $x$ mV/V at a full capacity of 1 lb, and using an excitation voltage of $E$ volts, the output voltage when fully loaded (1 lb) can be calculated as: $$ V_{\text{load cell}} = \frac{x \text{ mV}}{1000} \times E $$

3. Mapping the Load Cell Output to the INA129 Output We want to map the load cell output range (0 to $V_{\text{load cell}}$) to the output range of the INA129 (0 to +V or -V). Therefore, the maximum output voltage from the load cell needs to match the maximum output voltage of the INA129.

4. Calculate the Gain (G) Required The gain $G$ of the INA129 that we need can be calculated using: $$ G = \frac{V_{\text{out}}}{V_{\text{load cell}}} $$ Where $V_{\text{out}}$ is the desired maximum output voltage of the INA129, which is equal to $V$.

5. Relate the Gain to RG The gain $G$ of the INA129 is related to the resistor $R_G$ by the formula from the datasheet: $$ G = 1 + \frac{49.4k\Omega}{R_G} $$

6. Calculate RG Rearranging the above equation to solve for $R_G$ gives: $$ R_G = \frac{49.4k\Omega}{G - 1} $$

7. Substitute Known Values Insert the calculated values of $G$ into the formula for $R_G$ to find the appropriate resistor value.