I need to connect my modbus device to a DCS. The DCS has an RS232 modbus card. Now the only problem is that there is quite a long distance between (around 5 km) the DCS and my modbus device. Someone suggested that i can use a dial up modem to do this. Please help me. Also, besides dial up, is there any other way to do it?

 

Data radios are another option but I wouldn't consider it for a single modbus device. However if you have multiple fields devices in the same area it may make sense to use a master radio at the DCS and slave radios at the field locations.

Dial up modems may be your best option, provided you can get phone lines installed at both the DCS location and wherever your field device is located. If the field device doesn't have AC power then you can get some low power consumption modems that operate of DC power as well but you'll have to factor that load on whatever is feeding your field device power. Some field devices support an add-on modem card as well but you'll have to consult with the vendor to find out.

Under such a scenario you would purchase two modems and configure them such that the modem located with the DCS system always tries to maintain a dial up connection with the modem located with the remote field device. For infrequent communication your DCS system may support sending the modem dial and hang up commands to make the connection on demand. Again, you may want to check the DCS documentation or consult with the vendor to find out if that's possible.

There are also "short haul" modems/line drivers which can operate over 5km if you can bury some fiber or data cable from the DCS to the field device. Unfortunately I don't have much experience with those devices and laying cable is usually the last option most people want to entertain.

Best of luck,

Alan

 

A couple of ways to ponder.

http://www.blackbox.com/Catalog/Category.aspx?cid=381,1452,1471

 

Do it with wireless (radio)

Serial data radios can accomplish 5km with line of sight access (this means getting the antenna up on a tower) and directional antennae. Serial data radios are designed for RS-232; 232 in , 232 out.

Whether you need license wirelss or license free depends on your country and its regulations.

 

Westermo has a modem that supports both leased line and PSTN (dial-up). It also offer the ability to automatically fall back to dial up if your leased line fail.

all of the Westermo Range of modems support Modbus RTU - many do not.

http://www.westermo.co.uk (TD-34 or TD-35 Modem).

Best Regards
Ian

 

we use "industrial" modems from ERCO-GENER (http://www.gener.fr)(one for leased line or PSTN another for GSM) for that purpose and it works well. Dial up and hang is initiated through one of the alarm entries of the modem (the modem dials up when the entry is activated and hangs when transmission is completed). whe have hundreds deployed for remote alarm purpose.

 

You can connect serial devices to the dialup connection (PSTN/GSM/GPRS) with a serial device server (e.g. http://www.multenet.com/products/pocketpadrouter.html or http://www.multenet.com/products/duo.html).

Some/most serial device servers support Modbus Bridge, so you could use the existing Ethernet network (if available) to connect multiple devices to the dialup connection.

Another way may be to use Fiber.