8 bit controller for power meter

[songtt801234]

Hi guy,

Could you advise me, how to build a circuit to read currect from the source and feedback to controller ?

 

[KeepItSimpleStupid]

OK, is the source a 100 KVDC superconducting transmission line or a battery made from a lemon and two electrodes?

I won't play twenty questions (i.e. Is it bigger than a femtowatt), but more information is needed. Lots more.

What are you trying to do?

 

[songtt801234]

OK, is the source a 100 KVDC superconducting transmission line or a battery made from a lemon and two electrodes?

I won't play twenty questions (i.e. Is it bigger than a femtowatt), but more information is needed. Lots more.

What are you trying to do?

Thanks for your concern, i will keep you a update once i meet with my lectucer.
my project is tapping a single phase of power line.

 

[songtt801234]

Hi guy,

i am use hall feild effect current sensor to measure the single phase (230v) across a light buld or load . the sensor will give off the dc voltage and feed to mircocontroller.
Now my question is which is the correct model of hall field current sensor , which circuit of om-amp need to amlifier the signal , feed to mircocontroller.

thanks if you can provide me a good answer.

 

[KeepItSimpleStupid]

goto www.digikey.com and type hall effect sensor. The output will be AC or instantanous DC. You need to use v(t), i(t) for at least one period of v(t). Play with it with a spreadsheet. There is a good discussion with me and ratchet on this forum with an example spreadsheet. Numerical integration is in the cards. RMS is in the cards.

For starters play with v(t)=A*sin(wt) and i(t)=B*sin(wt+theta). Something you know the answer for.

Look up the calculus definition of RMS and numercal integration.
Watch out for degrees, radians and RMS. Understand power.
How might you isolate V? xformer? Do you have to? Protection?

There is lots of stuff involved if the load is not resistive. Power(W), apparent power, reactive power (var), power factor, Vrms, Irms etc

We don't do your homework.

 

[songtt801234]

thank you, keep it simple stupid.
i know the power triangle formula.
i more concern on the hardware side.
real , reactive , apparent power

 

[KeepItSimpleStupid]

I'm not sure you do know the software side.

But, if you dis what I asked, you would have ended up with something like this: **broken link removed**

Agan, there is the 20 question stuff. Yes, you mentioned 240 VAC, but not the max current expected. The sensor has to be sized for the peak current.

Note that the quiesent output is Vcc/2, therefore your A/D should be ratiometric with Vcc. The AC can be divided with a transformer (say a 240 to 12 Vac operated in reverse) and voltage divider. Sprinkle a little protection in the form of TVS's and your good to go. A wideband transformer would increase cost and be able to detect spikes.

 

[songtt801234]

i have a guy who is good in software. i more worry in hardware side.
i have some scope to focus in my reseach
1. hall feild effect current sensor "honeywell"
2. inductive current switch " Ak switch"
3. adc
4. signal conditioning
all the 4 point i have set the right path .
do you have good software to recommend to simulation the circuit - free please
i stay in asia , it hard to get a good software to simulation.
my the way you dont need to rest! haha .. thanks . mentor

 

[KeepItSimpleStupid]

The design is pretty straightforward as long as you don't want to capture high frequency glitches. the hall sensor inherently does isolation. A transformer inherently does isolation. Medical transformers are specified for this sort of thing.

It is important to transient protect your inputs because they are not lab quality sin waves. The current waveform can be all over the map with switchmode power supplies and the voltage will have limits primarily imposed by the power company.

Voltage can just be reduced using a transformer and a voltage divider and your pretty much there. You would probably want to reference this A/D converter to Vcc/2 as well where Vcc is likely 5V. If you don't you may run into quantization errors.

Simulation looks pretty tough for those devices. LTspice(linear) and TINA(from TI) are free.

One of the other issues would be how fast do you need to sample and the conversion time. By far a sample and hold flash converter is the fastest, but other types may do. Resolution is yet another issue.

Explain "2. inductive current switch " Ak switch""
Allegro might be a better sensor choice.

Lots of missing pieces. I don't know if this is a possible energy meter in which case there are chips such as from analog devices that will do a lot for you.
or is this say a power controller for a furnace which can be sloppy. If it's for a lamp, then you have to do it by measuring intensity.

 

[songtt801234]

hi mentor ,

i am so happy to read the data sheet of acs712 and i will use it and installation diagram to link to Adc.
my sigle phase will connect to 40watt light buld.

 

[songtt801234]

hi mentor ,

could you advise me.
i had install tina software on my laptop.
i need the spice model of allegro acs712 and import to tina software.
where can i find the netlist or spice model of allegro acs 712.

 

[KeepItSimpleStupid]

Can't help with a model.

 

[songtt801234]

Hi keep it simple ,

what would be the best soluction for the adc device. with it compatiable with allegro acs 712?

 

[KeepItSimpleStupid]

Ideally, you would like something that is 0-5V (rail to rail). Take a look at application #2. Look at the conversion times and the effects on what you have to read and the accuracies.

It doesn't really matter. I used a 30 A sensor because I didn't know what your after. You said a 40 W bulb. If this is incandescent, you have to account for the resistance being about 1/10 or 1/15 of what it would be for 40 W. Then you have to scale the RMS value x 1.414, so if it were say 1 A, you would be looking at +-1.414A if my math is right.
0 Amps is Vcc/2. Application #2, uses R1 and R2 to generate Vcc/2.

You want to make sure that your A/D can use an external reference. That external reference must be Vcc/2. It should not be a 2.5V reference. It really does need to be Vcc/2 created by either resistors or a real splitter.

A 30A part is way too big for a 40 W bulb. You know that, right? That's like 0.2 Amps RMS. But remember what I said and I'll let you figure it out. You need +- Amps or 0 to the +peak and 0 to the - peak AND you need to account for, or should account for, the temperature coefficient of tungsten. 10 to 15x less in resistance is just a "rule of thumb".

So, what you will get is an approximate 0-Vcc signal where zero is you max full scale -peak current and Vcc is your highest peak current and Vcc/2 is zero current.

If you shoot for something like 0.5 to 4.5 V at your designed currents you have room to play.

Since your reference is Vcc/2, that makes the system "ratiometric". Now it would be really convenient, if you could measure Vcc/2 and the output of the sensor with two successive conversions.

 

[songtt801234]

Hi keep it simple,

sorry for trouble you!
i had met with my lectuer , he dont want the hall field effect sensor, which you recommended!
He need a voltage tranformer and current transformer tap from single phase voltage.Which his critial, 97 % accurrate reading.
do you have any referance to read the voltage transformer or current transformer?

 

[songtt801234]

hi mentor ,

i am think of using Current Transformer VTX 151-1015 ( vigotronics) & voltage transformer VTX-120-3803-2045 vigotronics.
more component to build to signal conditioning .