It is advantageous to convert the analog signal into a digital signal, which is less susceptible to noise pick-up when transmitting analog data over long distances. It is very easy for noise to interfere the amplitude of a signal, but it would be harder to change its frequency.

HIGH NOISE IMMUNITY DATA TRANSMISSION1 circuit schematic

The TC9400 converts the input voltage into a pulse or square wave which is transmitted on a pair of wires by use of a line driver and receiver in the following system. At the other end, we can digitally displayed the original voltage (Vin) on a frequency counter or converted back to an analog voltage by use of a TC9400 F/V converter. [System’s block diagram source: Microchip Application Note]