Glossary · Industrial communication
Baud rate
Also known as: Symbol rate, Transmission rate
German: Baudrate
In data communication, the baud rate is the number of symbols transmitted per second on a communication channel. In simple serial links where each symbol carries one bit, it equals the bit rate, which is why the terms are often used interchangeably in automation.
- Industrial communication
In one sentence
The baud rate is the number of transmitted symbols per second; on simple serial links it equals the bit rate.
Example
All devices on a Modbus RTU line must be set to the same baud rate, for example 19,200 baud, or the master receives no valid responses.
How it applies
- Engineering: On serial buses such as Modbus RTU, PROFIBUS DP or CAN bus, every node must use the same baud rate. Higher rates shorten the cycle but reduce the permissible cable length.
- Commissioning: A mismatched baud rate, parity or stop bit setting is one of the most common reasons why a serial device doesn't respond. Some devices detect the baud rate automatically, others must be set with switches or software.
- Maintenance: When a device is replaced, the baud rate setting must match the rest of the segment. Default values of replacement devices often differ.
- Documentation: The documentation team states the supported baud rates, the default setting and how to change it, together with the cable length limits for each rate if the standard or manufacturer specifies them.
Baud rate vs. bit rate
The baud rate counts symbols; the bit rate counts bits. With modulation schemes that encode several bits per symbol, the bit rate is higher than the baud rate. For UART-based fieldbuses the two values are usually the same.