Data output form RBR loggers generally uses RS-232 protocol. Since many modern computers no longer have a suitable connection, it is possible to use a “serial-USB” converter module.
Currently we recommend EasySYNC ES-U-1001-A
RBR submersible loggers use an RS-232 serial line to communicate with the host computer. The loggers are supplied with a suitable cable to connect to the logger, having an industry standard DB9 female connector on the computer end. Because many computer manufacturers have discontinued providing RS-232 ports on their computers, particularly on laptop computers, the standard interface is now the USB connector. Therefore, to communicate with an RBR logger it has become necessary to use a USB to Serial adapter.
Though many USB to Serial adapters are available, they often lack detailed specifications. This means that some deficiencies can compromise communication with the RBR logger. The major problems with USB to Serial adapters are noted here and a recommendation follows.
RBR Logger Communications
- The RBR logger communicates using only three lines of the RS-232 protocol: Ground, Receive (Rx) and Transmit (Tx). RBR loggers do not use any form of RS-232 flow control (handshaking) available through other signals in the RS-232 protocol.
When using software other than the RBR Windows Software, ensure that all flow control is turned off (‘Flow control’ set to ‘None’). - The normal default baud rate of RBR loggers is 19200 baud. However, the default baud rate can be set to any of the values: 1200, 2400, 4800, 9600, or 19200 baud, depending on the preference for a particular application. When the logger data is being retrieved (downloaded), the RBR Windows Software will attempt to increase the baud rate to 115200 baud for a faster download. If the logger fails to respond properly at this baud rate, the Software will revert to the default to complete the retrieval.
RBR has seen problems with the high speed operation of some USB to Serial adapters. Some adapters will not work at 115200 baud, in which case the RBR Windows Software will recognize this and return to the default rate. Unfortunately, some USB to Serial adapters appear to operate at 115200 baud but in practice do not work properly. In such cases, individual data packets will be exchanged at 115200 baud. However, the USB to Serial adapter demands such lengthy timeouts that only one packet per second may actually pass between the logger and host. It may be possible to overcome this problem but it depends on the files provided by the manufacturer of the USB to Serial adapter. For example, a particular USB to Serial adapter, based on the FTDI chip set, supplied the information file FTDIPORT.INF. Part of the file is shown here:
[FtdiPort232.NT.HW.AddReg]
HKR,,"UpperFilters",0x00010000,"serenum"
HKR,,"ConfigData",1,01,00,3F,3F,10,27,88,13,C4,09,E2,04,71,02,38,41,9c,80,4E,C0,34,00,1A,00,0D,00,06,40,03,80,00,00,d0,80
HKR,,"MinReadTimeout",0x00010001,1000
HKR,,"MinWriteTimeout",0x00010001,1000
In this file the timeouts for read and write are set to MinReadTimeout = 1000ms and MinWriteTimeout = 1000ms. This means that for every write to the serial port, the USB to Serial adapter will wait one second before allowing the operation to continue, thus slowing the operation. If such a file is part of the USB to Serial adapter installation, take the following steps:
- Uninstall the USB to Serial adapter software (follow the steps in the instruction manual supplied with the adapter)
- Edit the .INF file so that both the timeouts are 100ms
- Reinstall the software.
Unfortunately, some installations do not use .INF files so no way exists to change these default timeouts. In such cases, try a different USB to Serial adapter.
