signal resistor (what is this, how's it work)

[hvacbear]

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.

[javajunkie]

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.

[19C]

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.

[adrianfromoz]

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

[ctaeke]

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.

[powerhead]

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!

[crab master]

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.

[ctrlguy]

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).