SRM-5A Short Haul Modem

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.

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Benefits and Features

  • Provides the easiest link for communicating with one datalogger 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 datalogger'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 datalogger'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 Datalogger: 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

Specifications

Data Rates Up to 9,600 bps
Transmission Mode Asynchronous, full duplex, 4-wire operation
Transmission Range 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.)
Altitude Up to 3000 m (10,000 ft)
Humidity Up to 95% (non-condensing)
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)

Compatibility

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.

Datalogger Considerations

Compatible Contemporary Dataloggers

CR200(X) Series CR800/CR850 CR1000 CR3000 CR9000X
*

Notes:
*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.

Compatible Retired Dataloggers

CR500 CR510 CR10 CR10X 21X CR23X CR9000 CR5000 CR7X

Frequently Asked Questions

Number of FAQs related to SRM-5A: 7

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  1. Campbell Scientific does not currently offer any. 

  2. Technically, the SRM-5A is compatible with the CR200X-series dataloggers, but it is more complicated to use it with these dataloggers. To use a SRM-5A with a CR200X-series datalogger, the SRM-5A must be in the DTE position on the station modem. In addition, user-supplied adapters and gender changers are needed to complete the connections between the SRM-5A and the RS-232 port of the datalogger. Contact Campbell Scientific for more information.

  3. It is not cost effective to repair. The SRM-5A should be replaced.

  4. Use the terminal mode of the Device Configuration Utility (select Unknown for Device type) set to 9600 baud. Click the Connect button to open the terminal screen.

    On the SRM-5A, short together the RCV + to the XMT +, and the RCV – to the XMT – connections. Try typing letters and numbers with the computer keyboard.  If these do not appear on the terminal screen, the modem is damaged and must be replaced.  Ensure that the Echo Input box is NOT selected.

  5. The FC100 is designed for lightning-proof and lightning-safe serial communication. Because the FC100 offers PMMA or glass fibers that are not conductive, electrical surges (such as those caused by lightning) cannot travel between the modems.
  6. If connecting to the CS I/O port, one of the following is needed:

    • An SC932A interface with a 15751 9 to 25 pin adapter
    • An SC932C interface

    A connection can also be made to the RS-232 port. However, the switch on the SRM-5A must be in the DTE position on the station modem, and adapters and gender changers may be needed to complete the connection.


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