Karthik,
You can not directly turn a sourcing output into a sinking output, however, you can adapt two sinking or two sourcing outputs to work with each through the use of pull-up or pull down resistors. In order to connect the [c]FP-CTR-502 (sourcing) with a function generator (sourcing), you will need to place a pull-down resistor
between the two. Specifically, you connect the In[x] terminal of the [c]FP-CTR-502 module to the Output of the function generator. In addition, you place a resistor between In[x] and Com of the [c]FP-CTR-502 module. The resistor size will vary based upon the voltage levels in use.
The function generator should be set to provide a unipolar output (e.g. 0 V ON, 10 V OFF, not -5 V ON, 5 V OFF) that is comparable in value to the
power supply wired to the V & C terminals of the [c]FP-CTR-502. If you have wired a 12 V supply to the [c]FP-CTR-502, you should set the voltage of the function generator to 0 to 12 V. The ON voltage must be more than ~3 V less than the supply voltage (see [c]FP-CTR-502 Operating Instructions for exact specs). The OFF voltage must be within ~1 V of the power supply voltage. When using a sinking input device, the polarity is reversed (0 V ON).
Regards,
Aaron