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Original question:

PGA970: can i use two nos of 3 wire HBt lvdt to one pga970 chip

PGA970: PGA970 multiplexing

Anuj Sharma40
Intellectual 360 points
Part Number: PGA970

Dear Scott,

   This query is regarding excitation of LVDT probe using PGA970. I would like to know if we can connect the PI of master PGA970 to 3 or more PGA970 slaves. If so, what is the maximum no. of slaves can the PI drive? I also would you to  share a schematic of multiplexing LVDT probes to one PGA970(with common excitation). Another question- What is the recommended value of  R & C required between PI & PE for frequencies of 5 and 13khz?

An early reply would be highly appreciated..

Thanks

Anuj

  • 0
    TI__Mastermind 31655 points

    Hi Anuj,

    So just to clarify, you would like to use the waveform generator output (PI) from a single PGA970 and split it out to drive into the PE input of 3 or more separate PGA970s each with their own LVDTs?

    And your second question is regarding multiplexing multiple LVDT sensors to a single PGA970? In that case, you would either need an amplifier to allow you to drive the excitation waveform to all of the LVDTs and not violate the output current limits of the PGA970 waveform gain, or you would have to multiplex the primary side excitation to the LVDTs, only hooking up the one that will be connected to the PGA970 inputs. Connecting the inputs is very straightforward, but you will need a separate MUX for each of the outputs of your LVDTs.

    For the filter, a simple RC lowpass would be sufficient. With cutoff frequency of 13khz, you could use a C of 10nF and an R of 1.2kohm as a starting point.

    Regards,

  • 0
    Intellectual 360 points
    Dear Scott,
       Thanks for your immediate reply. You have got all my queries right. Pl reply to the DAC query.
       With regards to the multiplexing method discussed, would it possible to scan say 4 separate sensors(lvdt probes) driven by a common excitation drive(using an external amplifier)  and an analog mux(such as 4052) and yet achieve high sampling rates of upto 500 samples per second? Would the demodulator be able to provide accurate results even being switched to different inputs continuously? Has this been tried and it would be nice if you can share some document or application note on this. Also is 4052 mux recommended for such an application? I am using a 3 wire half bridge probe.

    Thanks, 

    With Best Regards,

    Anuj Sharma
    Mobile- +91 8149002994
    Anusandhan Technologies, 
    F-107, Ashoka Plaza, Viman Nagar 
    Pune, Maharashtra, India 
    Landline no.:7028119793