What is the difference between a electronic expansion valve (EEV) and a thermostatic expansion valve (TXV) in an air conditioning system?

The TXV is purely a mechanical device, and uses a sensing bulb with a gas that expands or contracts with changes in temperature. This in turn opens or closes the valve. The EEV is more accurate and is capable of increasing or decreasing refrigerant flow based on information received. EEV can reduce energy consumed and provide better performance, but is also a little more expensive to install and maintain.