I have to measure voltage and current of a solar panel which gives 0-18 vdc and convert these two to an equivalent voltage of 0-5vdc. can anybody give me details about circuits?

 

To measure the output voltage, all you may need to do is hook up a couple of resistors to divide the output voltage down to the 0-5v level, unless your client device (meter, PLC, PC I/O card, etc.) needs input isolated from the solar panel DC output. If that's the case, buy a signal isolator from Phoenix Contact or someone like that.

To measure current, you will need a shunt, unless the output current is very small. A shunt is a resistor with an extremely small but precisely calibrated resistance. You run the current through the resistance and measure the voltage drop. Shunts are available for many different amp sizes and typically have output signals of 50 or 100mv, so you won't lose too much power in the shunt. You can buy amplifiers from the same companies as the isolators I mentioned previously to convert the milivolt signal to 0-5vdc. You will need an AC or DC power source for the device (and I doubt you will want to use the solar panel power).

 

Seems straight forward enough. Simply use a voltage divider, say 4.7k and 1.8k ohms. 18V across both of these draws only 2.76mA, which keeps source loading down to a minimum. You will find you can measure 0-5V across the 1.8k resistor.