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Overview
The SRM-5A, manufacted by RAD, is an asynchronous modem used for local communication between a datalogger and a computer. Two SRM-5A Short Haul Modems are required: one at the datalogger 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.
Read MoreBenefits and Features
- Provides the easiest link for communicating with one data logger over longer distances
- Low voltage transmission levels minimize crosstalk between adjacent lines within the same cable.
- Data are transmitted and received at a balanced impedance, providing excellent immunity to circuit noise.
- Transmits up to 6.2 miles using 19 gauge cable at 9600 bps
- Transmits up to 7.6 miles at 1200 bps
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Detailed Description
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.
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) |
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
Compatibility
Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.
Dataloggers
| Product | Compatible | Note |
|---|---|---|
| 21X (retired) | ||
| CR10 (retired) | ||
| CR1000 (retired) | ||
| CR10X (retired) | ||
| CR200X (retired) | ||
| CR206X (retired) | ||
| CR211X (retired) | ||
| CR216X (retired) | ||
| CR23X (retired) | ||
| CR295X (retired) | ||
| CR3000 (retired) | ||
| CR500 (retired) | ||
| CR5000 (retired) | ||
| CR510 (retired) | ||
| CR800 (retired) | ||
| CR850 (retired) | ||
| CR9000 (retired) | ||
| CR9000X (retired) | Although the CR9000X is compatible, the SRM-5A does not support the CR9000X's maximum communication rate and therefore may not be practical for many CR9000X applications. |
Additional Compatibility Information
Other Short Haul Modems
The SRM-5A is compatible with the now retired SRM-6A; the two can be used on either end of the same line.
Transmission Cables
Most manufacturers refer to cables compatible with this application as "PE39 Cable".
Suggested Cables for Burial
| Company | Part Number | AWG | Shield Type | Rodent Proof |
| Regency Anixter Anixter Essex Essex |
PE39 F-02P22BPN E-000622DFO BSWF BWFY |
19 22 22 22 22 |
.008 Aluminum .005 Copper Steel/Aluminum .008 Aluminum .005 Copper Clad Stainless Steel |
Yes Yes Yes No Yes |
For Suspension from Poles
| Company | Part Number | Outer Jacket | Messenger |
| Anixter | F-02P19AAF | 19 HMW Polyethylene | .109 extra high strength steel |
Additional hardware is required to hang cables; contact your local Anixter representative for details.
Specifications
| 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. |
| Dimensions | 5.2 x 5.2 x 1.8 cm (2.1 x 2.1 x. 0.7 in.) |
| Weight | 38 g (1.3 oz) |