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Multiple / Different source of analog inputs to PIC ADC multi input multi output syst

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DHANANJAYA L

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Dear Sir I am also facing problems for 3 phase individual line analog to digital conversion doing but i converted 230 volts into 5 volts using step down transformer on each phace but when i conected one phase voltage to pic circuit bord that phase voltage shows correct ADC results but other than this conneted pic chip phase its shows a abnormal voltages like 0, 5 volts fluctions. I think its problem for different phase voltages i.e refferenc volts is different from micro controller board so how can i connect common ground to board from each phase . but i still struggling please guide me how to maintain constant voltage on each phase on LCD. if you an any ideas plese send me vsl.innovation@gmail.com
 

Post your schematic.

Remember that voltages are measured across two points, if you are checking individual phase voltages you have to measure to a point common to them all, or, across phase to phase. The problem may be that your common point is not actually a 'zero' to measure from or it could be a problem with your rectification and filtering of each phase voltage. If you show us your schematic it will help to diagnose the problem.

Brian.
 

Dear Sir I am doing analog to digital conversion for three phase(415V-RYB) on LCD . I have done a single phase A2 D is correct but when i connect to other phase (i have supply to PIC from R- phase) like Y phase its value fluctuations like 0, 4,5..v. because this phase i not connected to supply board i.e PIC so its different for reference volts.

I have using step down transformer (230v to 12 V) on each phase then its using voltage divider circuits to 0-4 volts. how to give common reference to PIC chip.from other phase voltages i.e Y & B. I have to do using a single chip to measure a 3 phase volts without using multiplexer.


vsl.innovation@gmail.com
 

Star connect the transformer secondaries and ground the new low voltage neutral point in your MC circuit.. now put the voltage divider in other three points and give it to controller....


And i have to ask you, Did you put any rectifiers in the transformer output ???? At-least you have to introduce a Diode or Opamp.. You have to level it up to give it to controller.........
 

Venkadesh_M said:
Star connect the transformer secondaries and ground the new low voltage neutral point in your MC circuit.. now put the voltage divider in other three points and give it to controller....


And i have to ask you, Did you put any rectifiers in the transformer output ???? At-least you have to introduce a Diode or Opamp.. You have to level it up to give it to controller.........
Click to expand...



Yes Sir I have done but it is also same thing and also if i have connected rectifiers on each phase using transformers with filters its giving more voltage like i have step down transformer 230v to 12 v but it will give 18...20 v dc. wat my intension is i have to give direct ac volts because i/p volts vary o/p also same variation but when i use rectifiers circuits its not varied suddenly beause it was connected capacitors with diodes some charging volts it will decrees slowly i have to except sudden decrees the o/ps and also used optocoules using MC circuits supply variation its also same ...
 

Agreed - adding capacitors will average several cycles so the measurement will be slower to react to sudden voltage changes but please bear in mind that the PIC cannot measure AC directly. You must never allow the voltage at the PIC input to go below zero volts or it will be damaged. Your options are to rectify it and use zero detection to find the exact time to sample the peak of the cycles or to keep the full cycle but reduce it's amplitude, offset it's average and perform a waveform analysis. The first method is fairly easy, the second will need a high speed ADC and some complicated math.

Brian.
 

Which purpose Do you working with.... if you need just the RMS voltage, then you can rectify and filter (low capacitance with parallel resistor) and you can use it....
If you want all your phase details (zero crossing, frequency, amplitude) You can rectify it and use it without filtering, and if you have some more hardware knowledge then you can adopt zero crossing detector and rectifier filter combination.....
 

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