How Can I Maximize Output with LM331 Multiplier for Power Meter Design?

[syee10]

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? =)

 

[berkeman]

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? =)

What do you get for the output in your example? It looks like full scale is 10V? So what are the limits of your input signals?

 

[syee10]

The multiplier scale the output to 10V..means the output i suppose to get is 10 but it scale to 1. What i need is a multiplier that multiply a signal with another signal and i get the exact output of both inputs. My task is actually get the power of input Voltage and input Current by using a multiplier.

 

[berkeman]

The multiplier scale the output to 10V..means the output i suppose to get is 10 but it scale to 1. What i need is a multiplier that multiply a signal with another signal and i get the exact output of both inputs. My task is actually get the power of input Voltage and input Current by using a multiplier.

You need to condition and scale your inputs, so that you get the max of 10V at the output for the max power that you expect to be measuring. Scaling is all part of making a circuit like you are describing. What is the max power you want to measure (which will give you the 10V full scale output)?