Measuring phase differences between current and voltage

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glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

05 Mar 2005 16:51 slaa203a

Hi,

I am looking for pointers on how to measure the phase difference between voltage and current in a line, of course I am talkign about AC here and voltage level is 220V.

I am planning to use a microcontroller, so is it enought for the application or must I use a high end microcontrollers the 16 bit types or just a plain 8 bit micro, I hope I will not resort in using a DSP.

Thank you.

Glenjoy

gidimiz

Joined: 03 Feb 2005
Posts: 428
Helped: 77

05 Mar 2005 17:08 Measuring phase differences between current and voltage

Hi,

I worte this words in google, and i got a lot of good links:
measure the phase difference between voltage and current power line.
Try the 3 from the top, and see if you get your answre.
Good luck.

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

05 Mar 2005 17:16 Measuring phase differences between current and voltage

Hi,
Gidimiz, you are talkign about theoretical measurement, what I want is an actual measurement, and stepping down the voltage levels so I can use IC to measure its value and also measuring the current.

I think you must google first before you reply to my question if your reply fits my question.

the tran

Joined: 05 Dec 2003
Posts: 38
Helped: 4

05 Mar 2005 18:01 Re: Measuring phase differences between current and voltage

Hope you will find these links are helpful
http://www.analog.com/en/cList/0,2880,117%255F%255F43,00.html#139
http://www.analog.com/en/cList/0,2880,117%255F%255F43,00.html
http://www-s.ti.com/sc/psheets/slaa203a/slaa203a.pdf
http://www-s.ti.com/sc/psheets/slaa122/slaa122.pdf
http://www-s.ti.com/sc/psheets/slaa075/slaa075.pdf
T.L

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05 Mar 2005 18:01 Ads

aji

Joined: 04 Mar 2005
Posts: 23
Helped: 6
Location: Kerala,India

05 Mar 2005 20:13 Re: Measuring phase differences between current and voltage

Hi,
I am an electrical engg from india.I think you are measuring powerfactor.
for that first u have to step down 230v and connect it to an opto-coupler.Add resistor inthe current path and add opto coupler parallel to it.u should ensure I*R must be capable of driving led of opto.then using cature or counter feature of a micro find time interval between zero crossing of 2 waves .This count gives phase diff in terms of time.U can convert this any form
Regards
Ajith.S

fuzzy

Joined: 25 Sep 2004
Posts: 109
Helped: 10

05 Mar 2005 21:08 Re: Measuring phase differences between current and voltage

Long time ago I have a design power factor controller for industrial area.I design with 89c51.

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

06 Mar 2005 2:35 Re: Measuring phase differences between current and voltage

aji wrote:

So for the current path, it is the main line you are talking about here, is it possible not to cut the power line in measuring the current, quite impractical if I will be cutting the main line.

jojokatada

Joined: 13 Jan 2005
Posts: 257
Helped: 13

06 Mar 2005 5:17 Re: Measuring phase differences between current and voltage

you need to use step down/ measuring voltage/current ic CS5640A

aji

Joined: 04 Mar 2005
Posts: 23
Helped: 6
Location: Kerala,India

06 Mar 2005 7:06 Re: Measuring phase differences between current and voltage

Hi, I was talking in a general sense.U have to use CT for that.PIC canbe made zero
crossing detector by connecting 230ac line through a high value resistance to a pin line .Pic hasprotection diodes in the pins.Current can also treated like that if isolation is no necessary
i had pratically realized it by a pic and some resistors.
Ajith

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

06 Mar 2005 9:32 Measuring phase differences between current and voltage

Hi, CT stands for current transformer, am I right? I am not planning to cut the main line in measuring the current, the meter I am plannign to build is just an outlet plug-in, means I'll just plug it, then I'll get the reading.

So I am accepting inputs that can help me more in improving and enhancing my planned design.

Is it possible to measure the current of the mainlines just by using the hall effect sensors of allegro micro? Btw, could it be that when I measure, instead of measuring the main line current, it is the current of my system that I am measuring? So it will be an error.

Thanks.

aji

Joined: 04 Mar 2005
Posts: 23
Helped: 6
Location: Kerala,India

06 Mar 2005 10:54 Re: Measuring phase differences between current and voltage

Hi Glenjoy,

I think your idea is not realisable(ie you cannot measure pf of the whole circuit of a house by just plug in a device at an end.Hall effect senor will not ba solution to this.Refer any text books or web.There are optical sensor(Faraday Effect)but you cannot use that also in this project.You can only measure freqency and voltage by this method.You have connect in seris with the ckt to measure KW,KWh and pf
Regards
Ajith

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

06 Mar 2005 13:04 Re: Measuring phase differences between current and voltage

aji wrote:

Hi,

I think it is possible, have you seen the power factor correction used at homes? They are just plugged into household sockets. No wires are cut to put the ammeter in-between.

kumar

Joined: 26 May 2001
Posts: 154

06 Mar 2005 17:38 Re: Measuring phase differences between current and voltage

glenjoy wrote:

aji wrote:

Hi,

I think it is possible, have you seen the power factor correction used at homes? They are just plugged into household sockets. No wires are cut to put the ammeter in-between.

Hi!

The device that is plugged in for power factor correction is an AC Capacitor. This device does not measure pf and then correct it.

kumar

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

06 Mar 2005 17:53 Re: Measuring phase differences between current and voltage

kumar wrote:

glenjoy wrote:

aji wrote:

Hi,

I think it is possible, have you seen the power factor correction used at homes? They are just plugged into household sockets. No wires are cut to put the ammeter in-between.

Hi!

The device that is plugged in for power factor correction is an AC Capacitor. This device does not measure pf and then correct it.

kumar

Hi,

Kumar, sorry for that because I have not really seen a real power factor correction gadget, I just saw one in television the one advertised that can cut cost in electric bills.

Have you opened one of these gadgets? Are you sure that there is nothing inside but only a large capacitor and nothing else that measure the power factor and correct it based on the power factor read?

Thanks.

kumar

Joined: 26 May 2001
Posts: 154

07 Mar 2005 3:47 Re: Measuring phase differences between current and voltage

glenjoy wrote:

kumar wrote:

glenjoy wrote:

aji wrote:

Hi,

I think it is possible, have you seen the power factor correction used at homes? They are just plugged into household sockets. No wires are cut to put the ammeter in-between.

Hi!

The device that is plugged in for power factor correction is an AC Capacitor. This device does not measure pf and then correct it.

kumar

Hi!

Yes, there is nothing else but an AC Capacitor.

kumar

glenjoy

Joined: 01 Jan 2004
Posts: 1028
Helped: 47
Location: Philippines

07 Mar 2005 5:59 Measuring phase differences between current and voltage

Ok, if that will be the case, if you establishment or house has zero load and your power factor correction device is still plugged in, therefore your house will have a capacitive load and same effect your bill will just be the same.

aji

Joined: 04 Mar 2005
Posts: 23
Helped: 6
Location: Kerala,India

07 Mar 2005 7:14 Re: Measuring phase differences between current and voltage

Cheap devices assume that there is load and it is lagging.
Aji

nvd

Joined: 17 Jan 2005
Posts: 109
Location: Under Heavens

07 Mar 2005 7:43 Re: Measuring phase differences between current and voltage

You cannot measure the angle difference between current and voltage simply by plugging the device into an outlet. It's different for each device. If you connect a resistor across the outlet then the angle b/w voltage and current is zero. Your home load has a variable impedance. In that case the angle is variable. If you want to measure that angle, you must allow all of the current to flow through your meter. Regards.