| Author |
Message |
Chris Janus
Guest
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 Posted:
Mon Dec 13, 2004 8:08 pm Post subject:
Noise on the line? |
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I'm troubleshooting the following modem connection problem:
In a municipal application, a control panel senses the level of water in a
well, and transmits that information via modem to another control panel some
five miles away. That control panel adjusts the speed of the pumps wich feed
the well to maintain a desired level, and transmits som data back to the
well modem..
There is a modem at each control panel, and the connection is maintained
continuously on a dedicated phone line. The modems are off-the-shelf U.S.
Robotics 56K V.90 fax modems. If the control panels detect that
communication has stopped, each panel resets its modem and the control panel
at the well causes its modem to redial the pump control modem. This has
worked well for two years. Recently though, the modems have trouble
connecting if the "drive" which controls the pump's speed is on. (I believe
that the drive is generating some kind of electrical noise). If the drive is
turned off, the modems will connect and start to pass data back & forth, and
they will continue to communicate even when the drive is turned back on.
(There is not much data transmission, 4 bytes one way, then, 3 seconds
later, 16 bytes the other way, wait 3 seconds and repeat.) The problem seems
to be only in the handshaking, negotiating, or whatever it is that the
modems do to establish a connection and return the "CONNECTED" result code.
Setting baud rate lower and replacing both modems did not help.
So, in trying to understand the problem, I'm wondering why electrical noise
might interfere with modems tring to establish a connection, but not
interfere so much with modems maintaining connection once it has been
established.
Regards,
Chris Janus
jcjanusNOSPAM@erols.com |
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Reed
Guest
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| Posted:
Tue Dec 14, 2004 7:35 am Post subject:
Re: Noise on the line? |
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Chris Janus wrote:
| Quote: |
I'm troubleshooting the following modem connection problem:
In a municipal application, a control panel senses the level of water in a
well, and transmits that information via modem to another control panel some
five miles away. That control panel adjusts the speed of the pumps wich feed
the well to maintain a desired level, and transmits som data back to the
well modem..
There is a modem at each control panel, and the connection is maintained
continuously on a dedicated phone line. The modems are off-the-shelf U.S.
Robotics 56K V.90 fax modems. If the control panels detect that
communication has stopped, each panel resets its modem and the control panel
at the well causes its modem to redial the pump control modem. This has
worked well for two years. Recently though, the modems have trouble
connecting if the "drive" which controls the pump's speed is on. (I believe
that the drive is generating some kind of electrical noise). If the drive is
turned off, the modems will connect and start to pass data back & forth, and
they will continue to communicate even when the drive is turned back on.
(There is not much data transmission, 4 bytes one way, then, 3 seconds
later, 16 bytes the other way, wait 3 seconds and repeat.) The problem seems
to be only in the handshaking, negotiating, or whatever it is that the
modems do to establish a connection and return the "CONNECTED" result code.
Setting baud rate lower and replacing both modems did not help.
So, in trying to understand the problem, I'm wondering why electrical noise
might interfere with modems tring to establish a connection, but not
interfere so much with modems maintaining connection once it has been
established.
Regards,
Chris Janus
jcjanusNOSPAM@erols.com
|
If the "drive" is generating a *lot* of electrical noise, it is
possible that the modem handshaking could be affected. The process
is more sensitive than just sending data. I would try listening to
the line during a failure. Use a standard telephone with an RJ11
splitter. (or better, a "butt-set" if you have municipal telephone
folk you can borrow one from). Listen for noise when the drive is
on. Have you checked all wiring, especially grounding wires for
the whole system ??
--reed |
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Chris Janus
Guest
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| Posted:
Wed Dec 15, 2004 12:06 am Post subject:
Re: Noise on the line? |
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|
"Reed" <reedh@rmi.net> wrote in message news:41BE51A2.22E3B983@rmi.net...
| Quote: | Chris Janus wrote:
I'm troubleshooting the following modem connection problem:
In a municipal application, a control panel senses the level of water in
a
well, and transmits that information via modem to another control panel
some
five miles away. That control panel adjusts the speed of the pumps wich
feed
the well to maintain a desired level, and transmits som data back to the
well modem..
There is a modem at each control panel, and the connection is maintained
continuously on a dedicated phone line. The modems are off-the-shelf U.S.
Robotics 56K V.90 fax modems. If the control panels detect that
communication has stopped, each panel resets its modem and the control
panel
at the well causes its modem to redial the pump control modem. This has
worked well for two years. Recently though, the modems have trouble
connecting if the "drive" which controls the pump's speed is on. (I
believe
that the drive is generating some kind of electrical noise). If the drive
is
turned off, the modems will connect and start to pass data back & forth,
and
they will continue to communicate even when the drive is turned back on.
(There is not much data transmission, 4 bytes one way, then, 3 seconds
later, 16 bytes the other way, wait 3 seconds and repeat.) The problem
seems
to be only in the handshaking, negotiating, or whatever it is that the
modems do to establish a connection and return the "CONNECTED" result
code.
Setting baud rate lower and replacing both modems did not help.
So, in trying to understand the problem, I'm wondering why electrical
noise
might interfere with modems tring to establish a connection, but not
interfere so much with modems maintaining connection once it has been
established.
Regards,
Chris Janus
jcjanusNOSPAM@erols.com
If the "drive" is generating a *lot* of electrical noise, it is
possible that the modem handshaking could be affected. The process
is more sensitive than just sending data. I would try listening to
the line during a failure. Use a standard telephone with an RJ11
splitter. (or better, a "butt-set" if you have municipal telephone
folk you can borrow one from). Listen for noise when the drive is
on. Have you checked all wiring, especially grounding wires for
the whole system ??
--reed
|
The phone company came out to the site today (I wasn't there) and saw fit to
replace 600 feet of outdoor phone line, and replace a cracked phone line box
which they moved from the outside of the pump house to the inside.
The customer reports that the modem handshaking is working properly now,
even with the drive running.
I spoke with the serviceman before he started the job, and he said the same
thing
you did; he listens for phone line noise with a handset.
Thanks for your feedback.
-Chris |
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