need amplifier circuit for load cell output(mv) to milliamps, for giving input to the PLC
Consider the following simple circuit. 







simulate this circuit &ndash; Schematic created using CircuitLab

The Rin resistors connect to your bridge outputs. The differential voltage gain of the amplifier is Rf/Rin. Its output voltage is applied across Rshunt, which causes that voltage/Rshunt of current to be sunk by Q1 collector. C1 is to ensure stability.

Obviously you will need to bias the circuit so the output current falls in the range 4mA to 20mA with your range of bridge inputs. It may be that you need more gain than is convenient with a single stage, an instrumentation amplifier configuration (google) will be better for very high gain. 

Needless to say, the amplifier will need to be powered. Typically in 4mA to 20mA loops, and in fact the reason for the minimum current specification, is the amplifier power supply is taken from the loop current, this will mean that there also needs to be a minimum voltage that the loop supply will deliver, sufficient for the amplifier. The current output servo could be allowed to go down to 0mA in this case, with the power supply drawing a fixed 4mA. Or you could power it separately.