The LaMarche A31 Inverter is the ideal choice when AC power requirements are critical. Its ferroresonant transformer-based design and transistor switching provide an extremely reliable and high quality sine wave output (<5% THD). Applications may include the following systems: Computer, telecommunications, emergency lighting, offshore oil exploration, utility substation, security alarm, etc. The A31 has a wide range of standard features such as a sine wave output, voltage regulation, protection from AC-DC shorts, under/over-voltage conditions, input filtering and overload protection. It incorporates a DC input breaker and an automatic under/over-voltage shutdown circuit to protect the inverter. The A31 has a polarity indicator to tell you if the battery is connected incorrectly. The unit is equipped with an input filter precharge circuit, which includes an indicator to inform you that the inverter is ready for operation.

A31 Data Sheet 

A31 Instruction Manual