Post Go back to editing

CN0350 for Piezo strain

Hi, I have read your CN0350 , it seems design for a  piezoelectric accelerometer. 

Can I use it to measure the piezoelectric  strain ? How to modify it??

Thank you so much.

Lin

Hi Lin,

CN0350 was designed with piezoelectric accelerometers in mind.  I wouldn't recommend using the CN0350 to try and do piezoelectric strain because of the resolution needed from the converter.

We do have several other reference designs, which are developed specifically for load cells and strain gauges.  I think the best design to look at would be the CN0216.  There are 3 different boards that have the same circuit, so really the only difference is how you interface to the boards.  The [-ARDZ ] is an Arduino shield form factor, the [-PMDZ ] is a PMOD form factor, and the [-SDPZ ] connects up to ADI's demonstration platform.

I would take a look at these designs.

Cheers,

Brandon

  • Hello Lin,

    What performance do you require. What is the level of your signals from the strain gage., We have multiple ADCs that may suit. The AD7190 is a high-end low noise ADC with PGA. We have other parts also. If you send me your requirements, I can recommend parts.

    Regards,

    Mary.

  • Dear all:
    Thanks for all your reply.
    I may not write my demand clear.
    My application is not using strain gauge, instead, i want to use piezoelectric sensor, such as MFC, PVDF, or PZT to measure the dynamic strain.
    We are considering the Figure 2. Charge Input Signal Conditioning Circuit In CN0350 without using the AD7091R.
    However, our question is
    1. The Charge Input Signal Conditioning Circuit In CN0350 seems designed for acceleration, we don't know if it also fit the strain measurement? and how to modify it for strain measurement.
    2. The CN3050 mentions that "The AD8608 is chosen for this application because of its low bias current (1 pA maximum), low noise (12 nV/√Hz maximum) and low offset voltage (65 μV maximum). Power dissipation is only 15.8 mW on a 3.3 V supply. ". However, the 15.8 mW Power dissipation on a 3.3 V supply is higher. If it is possible to find others to replace the AD8608 for lower Power dissipation? (close to or Below 1mW ).

    Thank you so much.

    Lin

  • Hi Lin,

    The charge amplifier circuit in Figure 2 will work with a piezoelectric strain gauge, but there are several things to consider when selecting the amplifier.

    What is the bandwidth required of the circuit? This will depend on the frequency of the vibration or force applied to the sensor. The CN0350 circuit has a bandwidth of about 1MHz . It will handle signal bandwidths up to 100kHz. The gain-bandwidth product of the AD8608 is about 10MHz.

    If your sensor output frequency is less than 100kHz, then you can select from a number of CMOS op amps that have lower supply current and lower bandwidth.

    You can find the precision amplifier search table at:

    http://www.analog.com/en/products/amplifiers/operational-amplifiers/precision-amplifiers-vos-1mv-tcvos-2uv-c.html

    Sort on increasing Iq/amp and you can make the comparison between gain-bandwidth (GBW)  and supply current.

    A guideline would be to select an op amp with a GBW product at least 20 times that of the maximum signal you expect out of the sensor.

    Best Regards,

    Walt

  • Thank you Walt

    Very Useful.

    In the application of my sensor output frequency is near 10-20 Hz or below. 

    I have read the datasheet, the Iq/amp of AD8608  is 1.2mA, why the CN0350 said the Power dissipation is only 15.8 mW? how to calculate ?  

    Thank you so much.

    Lin

  • The CN0350 use 4 AD8608, so the  Power dissipation=4*3.3V*1.2mA=15.84mW. 

    Am right? 

    And does any tool can calculate the Power dissipation  of the entire system?

    Thanks

     

    Lin

     

     

  • Hi Lin,

    Yes, your calculation for the op amp is correct.

    There is no general tool for calculating the entire system power dissipation.

    You have to calculate the power required for each element and then add up all the powers.

    Thanks,

    Walt

  • ADA4051-2 is the lowest supply current I fund in the ADI web, is it suitable for my application?

    Thanks

  • AD8502 seems good in low power application.