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Energy Meter using VFC

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syee10

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Hi,

I am designing an energy meter. Assume that i have an input to the VFC LM331 and i get an output from the VFC which is a clock pulse. How am i going to connect this clock pulse to a decade counter and display it on 7 segment display to obtain the 'energy' unit? I prefer using any IC chips than PIC. Anyone please provide me any useful information.

Note that averaging the power(this is the output of VDC) over a period of time we get the energy.
 

I prefer using any IC chips than PIC.
No problem, you'll surely be able to find datasheets, e.g. for 7490 counter and 7447 7-Segment decoder. Wire the counters for the intended digit number and connect the pulse signal to the input.

P.S.: LM331 output is open collector and will need a pull-up resistor to VCC.
 
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    syee10

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Fvm,

Nice to see reply from you. Can i use 74ls90 and 74HC4511 insted of 7490 counter and 7447 7 segment decoder? actually i am confused with the counter.. how i going to make sure that the counter count each time is equal to 1second? means when it count 1 = 1s, count 2 = 2s and so on..
 

    V

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Can i use 74ls90 and 74HC4511 insted of 7490 counter and 7447 7 segment decoder?
Yes, but to keep the level specification exactly , HCT4511 would be needed at a TTL output.
how i going to make sure that the counter count each time is equal to 1second?
I didn't notice yet, that this assumption is incorrect:
Note that averaging the power(this is the output of VDC) over a period of time we get the energy.
Actually, power has to be integrated or summed up to get energy, not averaged.

Example: A LM331 output frequency of 1 Hz would represent 1 kW. If you count these pulses, you get kWs. No timebase is needed for this operation. If you want to display power, than you would need a timebase.
 
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    syee10

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FvM,

Can you tell me more about the output frequency of the VFC? Is the "output frequency of 1 Hz represents 1kW" is the true condition or just an example? Actually what in my mind is that the input of the VFC is the output of the analog multiplier which represents the power quantity (signal v(t) multiply by signal i(t)), am i right? I am confuse again about "If you count these pulses, you get kWs". Means each count in the decade counter represent 1s in practical?
 

is the true condition or just an example
I think, I clearly told it's an example. The actual relation depends on scaling of your power signal and the V/f scaling implemented with the LM331 circuit. I don't know about either.

Means each count in the decade counter represent 1s in practical?
No, it's not related to a time unit. With the scaling assumed in my example (it can be different) 1 count can mean e.g. 100 seconds multiply 10 W or 10 seconds multiply 100 W. The unit is energy measured in kWs.
 

FvM,

Can you explain to me how to scaling the part seconds multiply with power? say if i want 1000W multiply with 1second? How am i going to connect my circuit with the VFC LM331? Please explain with a simple schematic diagram if possible? Sorry im quite poor in this field
 

An energy meter displays energy, not power. If the input signal to the VFC is nonzero (you didn't tell yet, where it comes from, by the way), the energy meter will continuously count up and probably overflow, if it hasn't sufficient digits. If you look to a usual home electric meter, it has e.g. 7 digits, the lowest representing 0.1 kWh respectively 360000 Ws.

What scaling for the lowest digit do you want? What's the range of the VFC input signal in W?

With a VFC, you two optons to vary the scaling:
- adjust the VFC voltage to frequency factor
- use a prescaler respectively counter stages without a display
 

FvM,

Thanks for your fast reply. Ok i'll roughly tell you the system of the energy meter i want here by tonight. I'll prepare a block diagram so that you have a better idea of my problems. Thanks you so much.
 

I get the impression that you want to measure power rather than energy.
 

This will be my overall system block diagram

Actually the idea is refer to this system inside a journal

I am not following following the connections from the circuit given in the journal. I only use that idea and i construct my own connection. My problem now is the red rectangular area that i had marked. I dun really know why there is a D flipflop there and i dun know how to connect the counter and latch to 7 segment display. The 7 segment display is shows the value of energy and not the power or frequency.

Please help me. Thanks alot.
 

In my opinion, the shown circuit will measure (averaged) power, not energy.

But as I mentioned before, displaying energy with just three digits won't make much sense.
 

FvM,

From the journal it state that the final output is the energy unit. And the 3 digit is actually in the unit of kWh. But the journal however did not explain much about the circuit. Or maybe you can read through the journal perhaps?
 

Attachments

  • An electronic meter for measuring the saving in electrical power.pdf
    351.1 KB · Views: 52

All reported measurement result are in power units (W) rather than energy (Wh etc.). There are some references to energy measurement in the text, but not exactly related to the circuit. The actual cicruit is measuring power by counting VFC pulses over a defined gate time and latching the result. For a stable measurement, the gate time should be a multiple of the mains frequency, e.g. 1 s. Assuming the VFC has a scaling of 1 Hz/W, then a gate time of 1 s achieves a display in W, e.g. 0 - 999 W for a three digit display.
 

I also notice that the result and discussions part in the journal mostly are discuss about the power. Even the result of table 1-4 are all power and not energy. But i notice that in the abstract page 1, there's a sentence "For this purpose, this work presents an electronic circuit for the measurement of electrical energy". And also in page 2, "The product of these signals, when averaged over time, will yield a DC level proportional to the electrical energy consumed by the load. This signal is then digitized and displayed accordingly". And also Page 4, "The divided by N counter blocks are used to give the required units for measurements, i.e in (milliwatt-second, watt-minute, kilowatt-hour, etc.), where N is the number by which G is divided". And at the results and conclusion, " The technique presented in this work provides a very simple means for the digital measurement of electrical energy, which may be used over a wide range of energy measurement".
If the circuit is not measuring electrical energy in the end and not power, why there're sentences as i mentioned as above? Im really confused @.@
 

Im really confused

It's simple:
... 1 Hz/W, then a gate time of 1 s achieves a display in W
1 W/Hz = 1Ws (energy). If you count (integrate) it over 1s and display the count, you display Ws/s = W , which is power. If you simply let the counter run and display its content, you don't integrate over time, but "count" the consumed Ws, in this case your display shows the consumed energy.

But with only 3 digits, you'll soon get an overflow :sad:
 

erikl,

Thanks for your explanation. Could you provide me a simple schematic diagram connecting a output of VFC (you can just use a pulse source and give it a frequency?) with a decade counter and latch and finally a 7 segment display? Please assist me..

Thanks
 

erikl,

So what i need to construct now is actually a frequency counter? Which means i get the output of VFC (is a pulse with frequency 10-10kHz) and display it with a frequency counter is it? Just want to double confirm is my idea correct?
 

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