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  1. #14
    Join Date
    Dec 2003
    Location
    Nevada
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    1,815
    The advice to let the gaining company train you is good. Each one has a different philosophy so learn from the source. I have wrestled with each manufacturer individually and it almost requires different brains the stuff is so different.

    If I had to venture a guess it would be along the lines of cleaning the signal up.
    Quote
    “Engineers like to solve problems. If there are no problems handily available, they will create their own." Scott Adams

    "We can't solve problems by using the same kind of thinking we used when we created them."
    Albert Einstein

  2. #15
    Join Date
    Nov 2005
    Location
    Louisville, KY
    Posts
    8
    As a technical instructor, and having not seen the question, the two answers provided in this thread are the most likely answer(s) to your question:

    a) communications trunk end-of-line or termination resistor. Helps to ensure adequate signal level by drawing a specific amount of current on the communications trunk. Other factors must be met as well, such as the maximum number of connections to the trunk and the maximum overall length of the communications bus. For example, most RS-485 communications trunks use 120 ohm terminating resistors at each end of the trunk. How they connenct varies by equipment manufacturer (some have switches to connect/disconnect and on-board resistor, others require you to stick a resister under the bus terminals on the first/last device).

    or

    b) signal "conversion" resistor. Used to convert a current signal to a voltage signal. Ohms law is tells us that a 500 ohm resistor passing 20 mA DC will produce 10 volts DC. This is a useful solution if you have a sensor that produces a 0 or 4 to 20 mA signal and you have a controller that can only accept a 0 to 10 VDC input signal.

    Everyone is a "noob" at some point, and ideally, we all keep learning.
    I hope that this helps to explain things a bit better.

  3. #16
    Join Date
    Dec 2007
    Location
    Northern California
    Posts
    32

    Smile Mistor Quest

    WELCOME TO THE DARK SIDE. YOU WILL KNOW THE ANSWER,AFTER YOU
    HAVE GONE TO THE NEXT SERVICE MEETING IN SACRAMENTO. WELCOME
    AGAIN. CHILLER ROB TRAINED.

  4. #17
    Join Date
    Jun 2007
    Location
    Sydney, Australia
    Posts
    41

    Comms and Signal resistors

    I agree with javajunkie that these are your're most likely answers. A word of warning with regards using a 500Ohm resistor to convert 4-20mA to 2-10vdc. Current drivers are designed to connect to a theoretical 0 ohm load while 0-10vdc drivers are designed to connect to an infinite load. Therefore sometimes the 4-20mA source hasn't got the grunt to push through the 500 ohm resistance, resulting in a bad reading.

    I would only use the 500ohm resistor as a quick fix and you should use a signal converter as a permanent solution.

    regards
    adrianfromoz

  5. #18
    Join Date
    Dec 2007
    Posts
    5
    Ok, everyone seems to be wishy washy about this topic, I'll give it to you straight.

    A signal resistor is a plain old resistor! It does two things:

    1. Used to establish an EOL on a network trunk, and depending the trunk, its can be from 48ohm-500ohm. They are most commonly placed on RS-485 networks to eliminate signal bounce back, which will cripple just about an RS-485 network. Alot of controllers nowadays have these resistors built in, and usually a dip switch is used to put the resistor in the circuit. With the exception of DeviceNet, every other trunk type network I've seen needs a resistor somewhere to establish an EOL.

    2. In analog circuitry there is also a signal resistor. But its not something you would ever wire up(sometimes a jumper is used to enable it, like on JCI FEC controllers). It is built into the circuit board to filter the 4-20ma signal. Its very rare to see 0-10vdc signal circuitry with this resistor.

  6. #19
    Join Date
    Nov 2003
    Location
    Boston
    Posts
    600
    Quote Originally Posted by ctaeke View Post
    1. Used to establish an EOL on a network trunk, ............... With the exception of DeviceNet, every other trunk type network I've seen needs a resistor somewhere to establish an EOL.

    What's an EOL?
    What does it do?

    I hate secret code words!
    Edited by powerhead on more than one occasion

  7. #20
    Join Date
    Mar 2005
    Location
    Pacific Time Zone
    Posts
    4,206
    EOL - End of Line

    Use on a bus topology network in that each end of the wire in a segment has an EOL terminator to help keep the network wire at optimum levels for communication.

    There is also free/star topology networks in which you still use a terminator only you put in one somewhere in the middle of your network.
    "How it can be considered "Open" is beyond me. Calling it "voyeur-ed" would be more accurate." pka LeroyMac, SkyIsBlue, fka Freddy-B, Mongo, IndyBlue
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  8. #21
    Join Date
    Aug 2006
    Location
    New England
    Posts
    520
    A Lonworks network termination "resistor" is more than just a resistor. It's a resistor and a capacitor and the values of both are dependent on application (buss or FT).

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