How to convert output of the 4-20mA Transmitter to VDC?

4-20mA converted to 1-5 VDC 

You can convert 4-20 mA to 1-5 Volts DC simply with a precision 250 Ohms resistor in series with the measuring device to read volts instead of mA (and you may need protection so add a DC/DC converter, capacitance and other IC as required). For 0-5VDC (or other ranges) it is a little more complicated (see below).

According to Ohm’s law, V = R (E)

Therefore: with 4mA = 0.004 Amps and 20mA = 0.020 Amps

0.004 (Amps) times 250 (Ohms) = 1 Volt
0.020 (Amps) times 250 (Ohms) = 5 Volts

Conversely you can purchase an of the shelf product from virtually any component manufacturer (such as Analog Devices AD202 or AD204) to do this task.

Note: 4-20mA converted to 0-5 VDC/0-10 VDC

For 0-5VDC (or 0-10VDC etc) you need a standard Op Amp difference amplifier which you can look up from any component supplier. Four resistors and an Op Amp plus any bypass capacitors, etc. On the inverting input you set up 1 Volt with a voltage divider. You apply the 1 to 5 V to the non-inverting input. Both the divider and the signal are ground referenced. The gain on the difference amp should be 1.25 so 0V difference gives you 0V out and 4V difference gives you 5V out. Doing this for non-ground referenced signals gets more a little more complicated but the principle is the same.