The_Dutchman
Member level 1
Hello all,
For my thesis i'm designing a measurement device for measuring complex(real and imaginary part) impedance of an ultrasonic transducer.
The impedance should be measured from 1MHz to about 10MHz. The expected resonance frequency is about 5MHz where the sensor has an impedance of 150 Ohms.
For signal generation I am using an AD9834 DDS chip that can generate sine waves up to 75MHz.
My idea is to use the LM7171 opamp as driver. The ultrasonic transducers have a maximum average power of 0.125W.
I was planning to have a measurement range of about 50 Ohms => 1000 Ohms.
So if the impedance is 50 Ohms, and I use a drive voltage of 3Vampl => Iampl = 0.06A => Pampl = 0.18W => Pavrg =127mW
However I am neglecting phase shifts here. As the impedance increases I can also increase my voltage to the LM7171 its limits.
The ultrasonic transducer needs to be grounded, so the only method to measure the current through the sensor is with a shunt.
Herefore I would like to use 3 LM7171 amplifiers in an instrumentation amplifier circuit. Hower the voltage may not be to high, else the LM7171 cannot withstand the common mode voltage.
Now my questions, can I use 3 LM7171 amplifiers in an instrumentatin amplifier circuit to measure the current with the above specs?
Lastly, I am planning to use an AD8302 gain / phase detector, but I am wondering how I should connect the instrumentation amplifier to the input ? The input seems to be very low ? -74dBV = 223µV ???
Thanks in advance
For my thesis i'm designing a measurement device for measuring complex(real and imaginary part) impedance of an ultrasonic transducer.
The impedance should be measured from 1MHz to about 10MHz. The expected resonance frequency is about 5MHz where the sensor has an impedance of 150 Ohms.
For signal generation I am using an AD9834 DDS chip that can generate sine waves up to 75MHz.
My idea is to use the LM7171 opamp as driver. The ultrasonic transducers have a maximum average power of 0.125W.
I was planning to have a measurement range of about 50 Ohms => 1000 Ohms.
So if the impedance is 50 Ohms, and I use a drive voltage of 3Vampl => Iampl = 0.06A => Pampl = 0.18W => Pavrg =127mW
However I am neglecting phase shifts here. As the impedance increases I can also increase my voltage to the LM7171 its limits.
The ultrasonic transducer needs to be grounded, so the only method to measure the current through the sensor is with a shunt.
Herefore I would like to use 3 LM7171 amplifiers in an instrumentation amplifier circuit. Hower the voltage may not be to high, else the LM7171 cannot withstand the common mode voltage.
Now my questions, can I use 3 LM7171 amplifiers in an instrumentatin amplifier circuit to measure the current with the above specs?
Lastly, I am planning to use an AD8302 gain / phase detector, but I am wondering how I should connect the instrumentation amplifier to the input ? The input seems to be very low ? -74dBV = 223µV ???
Thanks in advance