The USB to Serial Adapter - Generally
A USB to serial adapter, also referred to as a USB serial converter or RS232 adapter is a small electronic device which can convert a USB signal to serial RS232 data signals. RS232 is the type of signal which is in many older PCs and is referred to as a serial COM port.
A USB to serial adapter typically converts between USB and either RS232, RS485, RS422 or TCP signals, however some USB to serial adapters have other special conversion features such as custom baud rates, high-speed or other.
Even the USB to serial adapter RS232 standard is an older communication protocol it is still used by many modern serial RS232 devices in both business and consumer markets and is also often used for personal and office serial devices.
More recently most new computers do not have a built-in COM port so a USB serial adapter is often used for connecting many types of serial devices to a computer. A standard USB to serial adapter is a very useful device for connecting equipment such as printers, scanners, scales and GPS devices, but also most business and consumer equipment can be connected to a computer by using an industrial grade adapter.
The USB serial adapter is made in different versions and grades, the 1-port adapter is very popular and one of the most commonly used adapters. Two to four port adapters are also frequently used if the user needs more than one serial port. Multi-port adapters can be connected to a computer by using just one USB cable, where after the computers operating system will create multiple virtual COM ports. Grades range from standard consumer grade to industrial grade and even mission critical grade adapters.
Most consumer grade USB serial adapters are not optically isolated or protected against high voltage spikes however most industrial grade adapters are optically isolated which means they are protected against voltage spikes and surges, ground-loops and most other voltages which potentially can damage the adapter or the connected serial devices.
The serial RS232 protocol has existed since the early 60'ties so you may wonder why it is still being used today. The reason is that it is a very reliable way of data communication and it is fairly easy to understand for engineers so it's easy to develop and program new devices. Another reason is that since the serial protocol has existed for such a long time, many devices already have the serial protocol built-in so its easy to integrate new devices with old devices.