auto-dialing modems


Thread Starter

Daniel Rallo

Hi all:

Does any kind of modem exist that can make calls to programmed numbers by switching a relay in a digital input?

With these working conditions, it's possible to receive calls, from the control center by operator's request for retrieving data?

This application is for remote monitoring and controlling electronic devices in whole territory where I only can supply Telephonic Basic Network.


Daniel Rallo
EMTE Sistemas, S.A.

Hullsiek, William

Why are people looking at auto-dialing modems instead of a low-cost router with dial-on demand ??

Generally in "modern" architectures, you use a router with dial-on-demand. When an alarm occurs, the distributed device sends an IP packet, the router then looks at the IP address. If not local, it should lookup the phone number(s) associate with the IP address sub-net.

Its too bad, the RTU vendors have not implemented a $200 - $300 router that could be mounted on DIN rail. Ethernet on one jack, and modem (RJ-11) on another jack.

William F. Hullsiek
MES Software Engineer

Ralph G. McDonald, P.E.

Hi Daniel

This is the same answer I gave to Robert several days ago but it still applies.

I have specified SIXNET industrial modems in some of our applications and had good results with them. I have included below the web address for the data spec's for their self dialing industrial modem. It sells for $475.00. You may want to check it out.

Hope this helps:

Ralph McDonald, P.E.

Ralph G. McDonald, P.E.

Hi William:

Many small PLC based remote systems do not have network capibilites but are still functional and cost effective for the application. They may not be the "latest and greatest" but the clients are happy with the price/performance ratio.

Using a auto-dial/auto-answer modem with a descrete input to start auto-dial for remote communications allows the remote system to call the head end or other units when conditions require. The auto-answer mode can allow the head end or other stations to call in.

We have used this type of system where leased line or long distance charges were high relative to other operating costs and radio modems were not an good option.

Hope this answers your question.