please help needed in lm324

[mohannad100]

hi every body
i need a circuit diagram to con vert 4-20ma to 0-5v using lm324 amplifier or lm741
i need the circuit diaram.
thanks .

 

[FvM]

I'm not motivated to draw a circuit diagram now. I just give a few hints.

1. Consider a shunt resistor. It already is a full featured current-to-voltage converter. You didn't tell any requirements regarding input voltage drop or convertor output resistance. You can scale the resisistor to get any intended conversion factor.

2. You requested a convertor, that has 0 V output a 4 mA input. This implies an offset. Actually a - 4mA offset current respectively a negative reference voltage with an additional resistor would solve the problem, without an OP.

3. But you want to use an OP. I may be useful, but I wanted to show, that it isn't necessary absolutely. The OP should be connected with non-inverting input to the shunt resistor, cause you want a positive gain. The OP also needs a negative feedback, let's connect a resistor from OP output to inverting input first. Now we have a +1 gain voltage buffer, we still need an offset.

4. Connecting a second resistor from inverting OP input to a positive reference voltage (could be the stabilized supply voltage for ease) introduces an offset. At the same time, the OP gets a >1 gain.

Now you have three resistors: The shunt and two resistors at the inverting OP input. You can form an equation for the output voltage, depending on input current, reference voltage and values of the three resistors. Calculate suitable values and you're done with the design.

Good luck.