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Modifying existing uniplar channel to measure AC signal for an unipolar DSP input

mike buba

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Hi, in my current solution I have only a spare channel for DC value (upper channel in the figure).
Recently, requirements changed and now I need synchronization with the grid, i.e. measure voltage and use PLL (phase locked loop). What would be the easiest and simplest solution to do that and get something like in the channel below?
In voltage transducer board can I scale and add offset so I can get the unipolar input to the exiting PCB board? Are there any other solutions? I am reluctant to do any modification on the exiting PCB board as it is really compact and all SMDs. Voltage transducer board input is +/-15Vdc and the output is measured signal.
 

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mike buba

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Resistor between U7A.3 and -5V node?
Can you please expand on this?
Output has to be unipolar from 0 to 3.3 Vdc for DSP's ADC. This channel is intended for a DC measurement. The channel below adds a 1.5 Vdc offset on U4A. Now, I need to use another AC measurement, but only have available (spare) DC channel. Is there something I can do on a voltage transducer output signal?
 

mike buba

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Sorry for the confusion, I wanted to suggest positive offset, resistor to +5 node, or another suitable constant DC voltage.
Thank you very much.
What is this called? I would like to research more and see if I can modify the resistor to add exactly 1.5 Vdc offset
 

danadakk

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Convert bipolar to unipolar with G modification, attached.


Regards, Dana.
 

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