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The SRM-5A, manufacted by RAD, is an asynchronous modem used for local communication between a data logger and a computer. Two SRM-5A Short Haul Modems are required: one at the data logger end and one at the computer end. Each short haul modem transmits over an unconditioned 4-wire telephone line or the CABLE2TP two-twisted pair cable. Data rates up to 9,600 bps are possible.
Campbell Scientific recommends connecting the SRM-5A to the data logger's CS I/O port via the SC932A interface; a 9-to-25 pin adapter is required. It may be possible to connect the SRM-5A to the data logger's RS-232 port, but configuration is more complicated; contact Campbell Scientific for more information. Surge protectors on both ends of the transmission line are strongly recommended.
Power Requirements
- At Computer: uses low power from the EIA RS-232-C/CCITT V.24 data and control signals
- At Data logger: combined current drain of the SC932A and RAD modem, which is 2.2 mA quiescent, and 10 to 15 mA active
- Protection: ac/dc over voltage connected via isolation transformers rated at 1,500 V RMS
Approximate Range with Various Data Rates and Wire Gage
| Wire Gage |
9600 bps Data Rate |
1200 bps Data Rate |
| 19 Gage (0.9 mm) |
10.0 km (6.2 miles) |
12.2 km (7.6 miles) |
| 24 Gage (0.5 mm) |
4.5 km (2.8 miles) |
2.8 km (3.4 miles) |
| 26 Gage (0.4 mm) |
3.3 km (2.0 miles) |
4.0 km (2.5 miles) |
| Data Rates | Up to 9,600 bps |
| Transmission Mode | Asynchronous, full duplex, 4-wire operation |
| Transmission Distance or Area | Up to 12.2 km (7.6 mi) depending on data rate and wire gage |
| Line Interface | 5-screw (4-wire and ground) connector block with cable strain relief inside plastic cover |
| Transmission Line | CABLE2TP (for short RS-232 or prewired enclosures) or unconditioned, 4-wire telephone line |
| Transmission Level | 6 dBm |
| Terminal Interface | EIA RS-232-C/CCITT V.24, female integral 25-pin connector |
| Operating Temperature Range | 0° to 60°C (Manufacturer's temperature specification is listed. Limited tests conducted by Campbell Scientific have shown the SRM-5A to perform at temperatures over -25° to +50°C.) |
| Current Drain at 12 Vdc |
|
| Altitude | Up to 3,000 m (10,000 ft) |
| Humidity | Up to 95% (non-condensing) |
| Service Requirements | Dedicated two-twisted pair cable connects one field station with base. |
