Discussion in 'General Electronics Chat' started by syee10, Oct 5, 2010.

1. ### syee10 Thread Starter Member

Mar 26, 2010
59
0
Hi,

I am designing a power meter which using the multiplier LM331 to multiply the Voltage and Current signal. The voltage and current signal will be go through the sample and hold circuit and the output of the sample and hold will be go into the LM331 multiplier. Power, P=VIcos(angle) and the LM331 having a transfer function of output W = [(X1-X2)(Y1-Y2)/10V]+Z. The problem is for example V=3V and I=2A, Output should be 6W(ignoring the cos(angle)). Due to the transfer function of LM331 i will never get the output 6W that i want. So anyone there can help me out? =)

2. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
203
An LM331 is a V to F converter IC, can you give us some additional details &/or examples of what exactly you're trying to do?

3. ### syee10 Thread Starter Member

Mar 26, 2010
59
0
Sorry marshallf3..i am using AD633 Analog Multiplier..typing error..my fault =) My task is in the previous statement..

4. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
203
Gotcha' - I know how it is to be working on several things at the same time.

5. ### gootee Senior Member

Apr 24, 2007
447
51
Well how would you be getting one of the inputs to be 2 Amps? You would have to sense the current somehow and convert it to a voltage, since the AD633 multiplies only voltages.

Your solution is in the scale factors (and the dynamic range you account for, with them).

You will probably sense the current with a small resistor, and use the voltage across the current-sense resistor as one of the AD633 inputs, possibly with a scale-factor amplifier before the input (or both inputs). And you could have a scale-factor amplifier after the output.

Figure out what the possible ranges of the actual voltage and current might be. Then figure out what current-sense resistance and scale factors you need to use.

Cheers,

Tom

6. ### syee10 Thread Starter Member

Mar 26, 2010
59
0
Thanks a lot Tom..I will try to think in the way you describe..I will post anything here if i still facing problems =) Have a nice day