You could use
sprintf (the documentation can be found here) to write your sensor value to a buffer (or string) and pass it to the OrangutanSerial class function
serial_send, which will transmit the data from the buffer to your data logger until all bytes (defined by size) have been sent. You can find more information about the OrangutanSerial class and its parameters in the "Orangutan Serial Port Communication" section of the AVR Library Command Reference.
If you continue to have trouble with your code, you can post it here, and I would be happy to take a look at it.