I am an intern in a Biomechanics Lab and we have an analog force sensor (http://www.jr3.com) with noisy output and we'd like to try to house clean as much noise without sacrificing any performance or inducing delay.
As far as the equipment associated with the analog force sensor, the inputs are shielded correctly. The grounding is sound, and good-grounding practices have been followed. Spike trapping is up for consideration, but I am told that an INA is preferable. The power supply has also been checked and is configured correctly. All of this has led the lab to the conclusion that an instrumentation amplifier would be the best "next-step" in cleaning up the signal.
I am new to circuitry, so I researched what I could and jumped in by building an INA from a design similar to the one on this link (**broken link removed**). I read through several articles on good INA design practice and built several iterations of this design according to them. I used the Op Amps from an LM324N chip, and tried many different combinations of resistor values, always ensuring (approximately) that R1=R3, R4=R6, R5=R7. To test the circuit, I varied Rg (R2 in Fig.) and calculated a theoretical output voltage from the equation on the same page (I kept R5=R4 because I read that that increased accuracy). The power supply to the chip was sufficiently more than the theoretical output, but still within the acceptable range. I measured the output voltage against a wall ground to determine the actual voltage. There was a relationship between the actual voltages and the calculated gains, but no where near the values of the theoretical voltages (especially for high gains >6). I can provide spreadsheets of the resistor values, gains, theoretical voltages, and actual voltages for the different circuits I have tested.
After failing to construct a functioning circuit from designs, I resorted to using an INA118P. Again, I varied Rg values and measured output voltage and compared it to the theoretical output voltage as calculated from the gain. I received the same kind of correlation between gain values and actual voltage output, but again they were no where near the theoretical values.
I searched for threads on instrumentation amps, but not found any that have been totally applicable to my predicament. I'm honestly not sure how to proceed, so any direction would be greatly appreciated.
Here are some specifications that have been requested on previous INA threads:
Signal Levels: +- 10V
Sensor Outputs: +-10V
Frequency of Signal (~20-60Hz)
As far as the equipment associated with the analog force sensor, the inputs are shielded correctly. The grounding is sound, and good-grounding practices have been followed. Spike trapping is up for consideration, but I am told that an INA is preferable. The power supply has also been checked and is configured correctly. All of this has led the lab to the conclusion that an instrumentation amplifier would be the best "next-step" in cleaning up the signal.
I am new to circuitry, so I researched what I could and jumped in by building an INA from a design similar to the one on this link (**broken link removed**). I read through several articles on good INA design practice and built several iterations of this design according to them. I used the Op Amps from an LM324N chip, and tried many different combinations of resistor values, always ensuring (approximately) that R1=R3, R4=R6, R5=R7. To test the circuit, I varied Rg (R2 in Fig.) and calculated a theoretical output voltage from the equation on the same page (I kept R5=R4 because I read that that increased accuracy). The power supply to the chip was sufficiently more than the theoretical output, but still within the acceptable range. I measured the output voltage against a wall ground to determine the actual voltage. There was a relationship between the actual voltages and the calculated gains, but no where near the values of the theoretical voltages (especially for high gains >6). I can provide spreadsheets of the resistor values, gains, theoretical voltages, and actual voltages for the different circuits I have tested.
After failing to construct a functioning circuit from designs, I resorted to using an INA118P. Again, I varied Rg values and measured output voltage and compared it to the theoretical output voltage as calculated from the gain. I received the same kind of correlation between gain values and actual voltage output, but again they were no where near the theoretical values.
I searched for threads on instrumentation amps, but not found any that have been totally applicable to my predicament. I'm honestly not sure how to proceed, so any direction would be greatly appreciated.
Here are some specifications that have been requested on previous INA threads:
Signal Levels: +- 10V
Sensor Outputs: +-10V
Frequency of Signal (~20-60Hz)