analog input 4 ... 20 mA SIMATIC S7-200

hi,

please, i need one advice about programming analog input (4 ... 20 mA) in LAD for S7-200. i have transmitter with input RTD 3- wire (0°C ... 150°C) and output 4 ... 20 mA. that output is wiring to the analog input AIW0 of the analog module EM235. when temperature sensor RTD reachs 75°C which is equally to 12 mA, must activate digital output(for example Q0.0 where is connected some lighting indicator like bulb). when value of temperature decrease below 75°C, digital output Q0.0 must be deactivate. so, according to these analog's terms, digital output must be activate or deactivate.
please, if someone know how that programming in the LAD, write, send a sketch!!!!!
i am new in analog signals, till now, i was only working with digital inputs and outputs.

thank You very much for any advice

On a Siemens S7-200 they actually use 0-20mA. 0mA = 0 in AIW? 4mA = 6400 and 20mA = 32000. Knowing the range of temperature you can scale it accordingly to convert to temperature. As for your digital output use a compare.

 Temperature    Output

----|>R|---------( )

      75.0

You may want to debounce the output some with a range or on/off delay as well.

Range:

 Temperature    Output

----|>R|---------(S)

      75.5        1



 Temperature    Output

----|<R|---------(R)

      74.5        1