This page documents the use of 900-MHz data modems in acquiring data from an RD Instruments Rio Grande acoustic Doppler current profiler (ADCP) without a direct wire connection between the ADCP and the computer running the data-acquisition software. The findings on the page are a result of a USGS Instrument Committee (ICOM) and Office of Surface Water (OSW) project to refine a tethered and remote controlled boat for use in making streamflow measurements.
The primary method used in initializing communication between the acquisition software and the ADCP causes compatibility problems with most 900-MHz radio modems. Because of this limitation, an alternate initialization method has been implemented in the Rio Grande firmware 10.07 or later and the latest version of data-acquisition software, WinRiver 10.00 or later. Use of the latest firmware and software available from the manufacturer is recommended to decrease compatibility problems.
To enable the alternate initialization method, also known as "Software Breaks," in WinRiver software:
Note that if a standard hardware break is attempted to be sent over some radio modems, the modems will need to be power cycled before communications can be reestablished with the ADCP. For further information on enabling the software break, consult the WinRiver Help files.
The Rio Grande ADCP, WinRiver software, and radio modems must all be set at the same baud rate for communications to be established over the radio modems.
To set the baud rate of the ADCP, connect directly to the ADCP using a communications program such as RD Instruments Dumb Terminal and issue the change baud rate direct command cb?11 (where ? is a number between 1 and 9 that represents the desired baud rate). After setting the baud rate, the save settings direct command ck should be issued to save the settings. For further information on setting the ADCP baud rate, consult the Rio Grande Users Manual.
To set the baud rate in WinRiver:
To set the baud rate in the radio modems, consult the documentation provide by the manufacturer for radio modems being used.
The direct command cl0 should be added in all WinRiver configuration files that will be used when collecting data with wireless modems. The cl0 command disables sleep mode on the ADCP. If this command is omitted and the ADCP goes into sleep mode, the only way to 'wake-up' or reinitialize the ADCP again is with the primary initialization method, a hard break. To send a hard break, the computer must be connected directly to the ADCP not connected to the ADCP over the radio modems.
Most radio modems are made to communicate between two computers. Because of this, the modems are wired the same as a null-modem cable (the send and receive pins get swapped between the two modems). To connect the modems to an ADCP, the send and receive pin-outs need to be reversed on one modem. This will wire the modems like the straight-through cable that the ADCP is designed to use. When wiring the modem to the ADCP, connect the wires from the modem connector to the corresponding wires on the Rio Grande bulkhead as indicated in the table below.
Table 1. General radio modem to ADCP pin-outs.
|
Standard 9-pin Connector |
Standard 25-pin Connector |
Freewave DGR-115W Connector |
Rio Grande lpmil-8 Bulkhead |
Description |
| 2 | 3 | 2 (Red) | 1 | RS-232 in |
| 3 | 2 | 3 (Orange) | 2 | RS-232 out |
| 5 | 7 | 5 (Green) | 3 | Signal Ground |
| 10 (Black) | 4 | + Power (12 volts DC) | ||
| 5 | RS-422 out A (not used) | |||
| 6 | RS-422 out B (not used) | |||
| 7 | Spare (not used) | |||
| 9 (White) | 8 | - Power (Ground 12 Volts DC) |
Custom cables can be obtained from Impulse Enterprise which manufactures cables that connect to the Rio Grande bulkhead.
Wiring example using Freewave DGR-115W
radio modems
with a custom cable from Impulse
Enterprise.
Cable-wiring diagram in Word format.
Remarks: Problems were encountered initializing the ADCP. However, when initialization was completed successfully, data loss because of communication errors was low during bench and field testing. Modem specifications indicate that the modem supports baud rates up to 115,200 baud, but during testing the modem began to have some problems with data loss at 57,600 baud. Data loss at 57,600 baud would at times exceed 50 percent. Communication with the ADCP could not be established at 115,200 baud. The modems do not come in an environmental enclosure. Operates on 12-volts DC.
Note: For this radio modem, pins 8 and 20 from the 25-pin connector on the modem connected to the ADCP should be wired together.
Manufacturer: Freewave Technologies, Inc.Remarks: During testing, modems operated with little data loss for the full range in baud rates (the maximum being 115,200 baud). Modems come in a waterproof enclosure and have been very reliable during repeated field use.
Manufacturer: Teltronics International, Inc.Remarks: Designed for office use. The modem is not housed in an environmental enclosure, and communication sometimes is lost when operating in extreme temperatures. The modems worked during testing at baud rates up to 38,400 baud, with data lost because of poor communications; data loss varied from little to approximately half of the expected data. This variability seemed to be greatly affected by the surroundings and the length of time during which data were collected. Operates on 12-volts DC.
Note: For this radio modem, flow control should be disabled (modem command AT\Q0).
Manufacturer: Young Design, Inc.
Model: 910
Remarks: Modems have just been received for testing. Modems will be tested for compatibility with RD Instruments Rio Grande. Modem specifications indicate that the modem supports baud rates up to 38,400 baud. The modems do not come in an environmental enclosure. Operates on 12-volts DC.
If you have used or attempted to use a radio modem not listed here with an ADCP, please send your results to Mike Rehmel. Any new information on using radio modems with ADCP's will be added to this page as it becomes available.
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