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RS232 Interface Board Frequently Asked Technical Questions
RS232 is well understood, inexpensive and reliable. It is supported by a large number of chips and by industrial machines that have an RS232 input or output. It works perfectly well if transmission distances are under 50 feet (15 meters), data rates are 19,200 baud or less, and only a limited amount of data is to be transmitted, like readings from a digital panel meter. Introduced in the early 1960’s, RS232 is the oldest serial communication standard still in use.
Compared to later interfaces like RS485 and Ethernet, RS232 has lower transmission speeds, a shorter maximum cable length, larger voltage swings, larger standard connectors, and no multi-point capability for digital addressing. Starting in around 1990, new computers ceased to offer an RS232 port, switching instead to multiple USB ports to support peripheral devices.
The L232 communication board available with Laureate meters comes with an RJ11 connector, while most PCs come with multiple USB connectors. To join the RJ11 connector of the meter to a USB connector of the PC, use a combination of two Laurel cables CBL01 and CBL02. These plug into each other via mating DB9 connectors, as described in our Cables web page. The critical cable is CBL02, which contains an FTDI RS232-to-USB adapter chip that is compatible with all versions of Windows, not just Windows XP.
The Laureate USB communication board is a good choice to connect a Laureate meter to the USB port of a PC if data transmission distance is 16 feet (5 meters) or less. The data cable can then be a standard USB cable with A and B USB connectors like Laurel’s CBL05 cable, as described in our Cables web page. The Laureate USB board LUSB and RS232 board L232 have the same cost an offer the same data rates. Stay with RS232 if you need to connect to a device with an RS232 port.
RS485 is the preferred serial communications standard for long distance industrial communications. It uses balanced differential signals for send and receive. This provides high noise immunity and allows distances up to 4,000 ft (1200 meters). RS485 is specified for multi-point communications where multiple instruments have their own address on the same communication line, while RS232 is only intended for point-to-point communications.
The answer is no. RS232 does not allow multiple meter to transmit data on the same RS232 line. Use RS485 instead. However, two Laureate 6-digit remote displays can be addressed and listen on the same RS232 line. Having more than two remote display would pull down the signal voltage.
Laureate meters and LT series transmitters with RS232 support Laurel’s ASCII character based Custom ASCII protocol and the world-standard Modbus RTU protocol and. Both protocols (or communication languages) are built into the instrument’s firmware and are user selectable.
RS232, USB and RS485 used in a non-addressable point-to-point mode support continuous data streaming, which is selectable in the Custom ASCII protocol. This mode allows analog readings to be output at rates up to 60 per second or at specified time intervals. It allows frequency readings to be output at rates up to approximately 30 per second, limited only the user programmed Gate Time or one signal period, whichever is longer. The Command Mode of the Custom ASCII protocol or the Modbus RTU protocol is limited to about 2 readings per second.
Laureate meters are modular with a middle slot reserved for a communication board like the RS232 board, as illustrated in our Laureates Overview web page. Boards can be ordered installed with a new meter, and they can also be purchased separately later and be simply plugged in. The presence of a new board and the type of board are automatically sensed by the meter’s firmware or by Instrument Setup (IS) software. If you change boards, also change the model number on the meter label.
Use Laurel’s free XLOG2 datalogging software. That software is described in our web page at https://www.laurels.com/datalogging-software.phpand user manual at https://www.laurels.com/downloadfiles/datalogging-manual.pdf .
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