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anupteke
Joined: 09 Nov 2008
Posts: 18
Location: India
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 22 Nov 2008 18:20 ac voltage measurement |
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Hi guys
Im doing project on AC line voltage measurement by MCP3201 and 89C2051.
Im facing problem in AC to DC conversion by rectifier and filter response.
so can anybody tell me any other direct measurement technique of AC voltage measurement.
Thanks
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are
Joined: 16 Nov 2004
Posts: 81
Helped: 5
Location: Balen (Belgie)
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22 Nov 2008 21:52 Ads |
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Sinisa
Joined: 03 Mar 2003
Posts: 337
Helped: 66
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anupteke
Joined: 09 Nov 2008
Posts: 18
Location: India
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23 Nov 2008 6:14 line voltage measurement |
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| but RMS TO DC converter IC's are very costly...
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FvM
Joined: 22 Jan 2008
Posts: 5160
Helped: 767
Location: Bochum, Germany
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23 Nov 2008 15:53 ac voltage measure circuit |
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| Quote: |
| but RMS TO DC converter IC's are very costly... |
I don't think very.
However, you did neither tell what you exactly want to achieve nor which problems you experienced. My general comment is: I never had problems with AC measurements. I use RMS measurement if required and simple rectifier otherwise. Also digital signal processing as suggested by are is an interesting option to my opinion.
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anupteke
Joined: 09 Nov 2008
Posts: 18
Location: India
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23 Nov 2008 17:53 measure line voltage |
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look FvM im doing project on measuring AC line voltage and display it on LCD. I'm using 89c51 for it and 2x16 line LCD. 1st i have done ac to dc conversion using simple bridge rectifier. at the output of rectifier i have connected 100uf capacitor.
and using 10K 10 turn POT i'm setting voltage to ADC (MCP3201) as 1 volts for 100 volts AC. and 4.096V as reference to ADC. and this whole setup working well.
now if u vary the input AC voltage by Dimmer from say 230V to 180V the display show this change slowly i.e. the output from rectifier changes slowly becoz of 100uf capacitor.
so if you replace that 100uf capacitor with lower value and suppose input voltage is 230V and steady, the displayed value of voltage of LCD changes (fluctuates) do to ripples in rectified DC.
so if we increase capacitor value to decrease ripples it reduces response time of circuit and if we decrease capacitor value to increase response time it increases ripples in DC.
so what should i do????
Thanks[/img]
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FvM
Joined: 22 Jan 2008
Posts: 5160
Helped: 767
Location: Bochum, Germany
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23 Nov 2008 18:05 voltage measurement ic |
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Normally, the rectified mean value is a usual parameter in AC measurement. Using a rectifier with a capacitor as in a power supply, you rather measure a peak than a mean value, which would be unwanted, I think. A suitable selection of time constant is another question, it has to be answered according to your application. To reduce mean value ripple, a higher order low-pass can be used.
To my opinion, an OP full-wave rectifier circuit, as shown in any circuit design text book or OP manufacturer application notes, followed by a 2nd or 3rd order low-pass should work. Another option to remove the ripple is synchronize the ADC sampling with mains frequency.
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anupteke
Joined: 09 Nov 2008
Posts: 18
Location: India
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23 Nov 2008 18:14 ac voltage measuring |
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do you have sum schematic of that.
i tried simple rectifier followed by 2 RC low pass filter with C=22uF and R=15K.
but now when i turn on power after long time it shows correct value and if i turn off and turn on power quickly then it shows different value on LCD which is less than actual.
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saeed_pk
Joined: 20 May 2006
Posts: 199
Helped: 5
Location: Islamabad, Pakistan
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24 Nov 2008 10:33 rectified means value for voltage |
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I might happen because when you switch off and on CAP are not discharged and your MCU reads that half-discharged value, use a better filter
A better way is to consult Microchip Application Note ( AC Line interfacing) There will be no use of Filter
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anupteke
Joined: 09 Nov 2008
Posts: 18
Location: India
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25 Nov 2008 12:23 dc voltage measurement ic |
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thanks saeed_pk
i saw that application note. How can i use this technique in MCP3201 with 89c2051??
do you have any schematic to measure AC line voltage???
Thanks
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