Features
- Includes RJ11 connector for use with a 4 or 6-wire data cable
- Cable assembly available for direct connection to a PC DB9 COM port
- Suitable for point-to-point data communications
- Suitable for all 1/8 DIN Laureate DPMs, counters, timers & remote displays
- Selectable Modbus RTU or Custom ASCII protocols
- Selectable baud rates to 9600
- Isolated from meter and power grounds
Certificates of Compliance
The Laureate RS232 serial communication board P/N L232 allows a Laureate 1/8 DIN digital panel meter, counter or timer to be interfaced to an external PC, a serial input remote display, or other device. Connection to a PC allows programming via Laurel's free Windows-based Instrument Setup Software, or to output readings to a PC for display and datalogging using Laurel's free XLOG2 software.
RS232 is normally only used for point-to-point communications via a single data line. The RS232 request-to-send line (RTS) can be set to a latched mode, where a single reading is transmitted when the line is taken high momentarily. This mode allows a single data transfer to be commanded by another device.
RS232 can drive a 6-digit Laureate remote display or a Serial Input MAGNA large digit display. These units can use the received RS232 datat to display readings, to switch relays for alarm or control, and to generate a scaled analog output, such as 4-20 mA or 0-10V. Two Laureate 6-digit remote displays can be connected to a single RS232 line in multidrop fashion without loading down the RS232 driver and be digitally addressed.
If multiple meters are to be digitally addressed by a PC or PLC, use our RS485, USB, Ethernet or WiFi boards, as listed in Laurel's communication board selection page.
Two serial protocols are user-selectable for RS232: Modbus RTU and Custom ASCII. Modbus RTU is an international Master-Slave protocol which works in a Query-Response command mode, and it requires use of an external Modbus Master. The text string based Custom ASCII protocol is the simpler of the two and is recommended if the Laureate is the only instrument on the data line, as would normally be the case with RS232. It can be set to a command mode or a continuous data streaming mode to send serial data in the absence of an external Master. For information on our protocols, please see our communication user manuals.
Installation
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CBL01 cable. Includes DB9 and RJ11 connectors to connect a Laureate with an RS232 board a PC RS232 COM port. Plugging into the Laureate is the RJ11 connector of a common 6-wire data cable. Plugging into the COM port of a PC is custom-wired DB9-to-RJ11 adapter, which accepts the other end of the 6-wire data cable. The DB9-to-RJ11 cable assembly is sold by Laurel as P/N CBL01. |
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CBL02 USB-to-RS232 adapter. Includes USB and DB9 connectors. Combined with a CBL01 cable (illustrated), it allows a Laureate meter with an RS232 board to be connected to a PC USB port. Note that Laurel also offers a USB board, which allows a Laureate meter to be connected to a PC USB port using a standard USB cable. |
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Electrical Specifications
| RS232 Board Specifications | |
|---|---|
| Laurel Part Number | L232 |
| Connection | RX, TX, GND, RTS (optional) |
| Data Rates | 300, 600, 1200, 2400, 4800, 9600 baud |
| No. of Devices on Data Line | 1 (point-to-point) |
| Connector | Single RJ11 jack |
| Line Length, Max | 50 to 1000 ft (15 to 300 m) depending on cable and data rate |
| Isolation | 250V rms working, 2.3 kV rms per 1 min test |
| ESD Protection | 15 kV per IEC 1000-4-2 |
| EMI Immunity | 10 V/m per IEC 1000-4-3 |
| EFT Protection | 2 kV per IEC 1000-4-4 |
| Short Circuit Protection | Continuous |
| Selectable Protocols | Modbus RTU, Custom ASCII. |
Protocol Specifications (protocols reside on Main Board)
| Modbus RTU | |
|---|---|
| Standards Compliance | Modbus over Serial Line Specification V1.0 (2002) |
| Protocol Type | Master-slave, query-response command mode |
| Data Streaming Mode | Not supported by Modbus specification |
| Data Formats (selectable) | 1. No parity, 8 data bits, 2 stop bits |
| 2. Odd parity, 8 data bits, 1 stop bit | |
| 3. Even parity, 8 data bits, 1 stop bit | |
| Applicable Interface Boards | Ethernet, USB, RS232, RS485 |
| Conversion to Modbus TCP | Automatic for Ethernet |
| Main Board Revision Level | Level 5 or above |
| Custom ASCII | |
| Standards Compliance | Laurel proprietary protocol |
| Data Format | No parity, 8 data bits, 1 stop bit |
| Protocol Type | Text string based command mode or continuous data streaming mode |
| Data Streaming Mode | User selectable for up to 60 readings/sec |
| Applicable Interface Boards | RS232, RS485, USB |
| Main Board Revision Level | Any |
Laurel Software Requiring a Communications Board
- Instrument Setup Software runs on a PC and provides a Windows Graphical User Interface (GUI) as an alternative to programming the meter from the front panel. This software can be downloaded from this website at no charge. Its use requires a serial communications board in the meter, but following setup that board can be removed if desired. Compatible with Modbus or Laurel ASCII protocol.
- Custom Curve Linearizing Software is compatible with the Extended option version of all Laureates. Not applicable to temperature. Custom curve linearization can provide exceptional accuracy from low cost transducers and extend their working range on the high and low ends. This software can be downloaded from this website at no charge. Meter setup requires a serial communications board in the meter and the Laurel ASCII protocol, but following setup that board can be removed if desired and any protocol can be used.
- Data Logging Software turns a PC into a data logging system. The RS232 board allows data logging with a single meter. Use of RS485 boards allows data logging with up to 31 Laureate instruments. Data can be logged from selected meters into an ASCII file, which can then be imported into MS Excel. Data can also be displayed on the computer screen in the form of up to 64 actual or virtual panel meters in 4 groups (or screens) of up to 16 meters each. Compatible with Laurel ASCII protocol only.
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.
See page 7 of the Laurel digital panel meter manual , page 7 of the Laurel counter manual, page 8 of the Laurel scale meter manual, or page 8 of the Custom ASCII protocol manual.
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 .
