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

[quest]

Hi guys---

Anybody know what a signal resistor is and how it works?

I think it's geared towards something large like a chiller.

Any help would be much appreciated.

[nick0danger]

We have used them on Automated Logic controls, to tell the AR or VAV controllers its is the end of the line, and to loop the communication back up the line. Not sure if thats the Answer but it could be.

[kashka]

I'm not sure if you are referring to a terminating resistor; if so, it is typically used at the end of a bacnet network to eliminate any noise that is present on the network.

I've not heard the term signal resistor.

Hope this helps.

[quest]

Many thanks guys--

I just completed a 6 month course in HVAV/R and learned tons of stuff.

The job I want is working for a large chiller and boiler service company.

Unfortunately we spent very little time covering these topics in class.

I told my teachers at school that I was leaning towards working on the "big stuff" and they said usually you get your training through the company that hires you.

I've been through 3 interview's with a company that works on the larger equipment and they gave me a test with 120 questions---I got 25 right

Then my mentor sent me out with my test and asked me to find the answers to the questions I missed by any creative means possible. It's been some work finding the right answers and understanding the concept behind them but that is half of the fun right?

[supertek65]

Hi guys---

Anybody know what a signal resistor is and how it works?

I think it's geared towards something large like a chiller.

Any help would be much appreciated.

keep learning grasshopper
sounds like a hard test

frank

[quest]

Thanks Frank--

It is a hard test kinda like trying to cram 15 to 30 years of many "experts" hard earned knowledge into a sleepless week.

If this thing works out I'll be starting at the bottom and working my way up so you can bet you'll be seeing me around more trying to get a better understanding of this trade.

[nickolas]

Signal Resistor?

Has no bearing on boilers chillers or controls

probably micro electronics

[ctrlguy]

I'm wondering if it's not just a 500 Ohm resistor used across a 4-20mA signal to convert to 2-10VDC.

[crab master]

Or is it an electronic transducer?

Say take a 0-10VDC signal to a resistive output.

Like here http://www.kele.com/olcat/OT8/res-1e.pdf

[kashka]

Many thanks guys--

I just completed a 6 month course in HVAV/R and learned tons of stuff.

The job I want is working for a large chiller and boiler service company.

Unfortunately we spent very little time covering these topics in class.

I told my teachers at school that I was leaning towards working on the "big stuff" and they said usually you get your training through the company that hires you.

I've been through 3 interview's with a company that works on the larger equipment and they gave me a test with 120 questions---I got 25 right

Then my mentor sent me out with my test and asked me to find the answers to the questions I missed by any creative means possible. It's been some work finding the right answers and understanding the concept behind them but that is half of the fun right?

I am interested in seeing the questions on your test. Would you mind sending me a copy if possible. I would like to see how much I can answer.

I've been doing controls for about 6 years and mot of it was OJT, but I have an electronics background, so most of the control logic came easy. I still get a little flustered on the mechanical side of things though.

Thanks,

[quest]

Kashka----

Wish I could help as it is one awesome test!!!!! Like one large puzzle!!!!

I did not make the test---Somebody with many years of training and hard earned experience did. (Hope to know as much someday)

I gave my word that I would not distribute the test and would return it upon completion.

Sorry it is not mine to give---only on loan for a spell from some cool people.

Hope you can understand

[amigo]

Hope you can understand

Unless you can give us the exact question and the context it was used in, all you will get from most of us are our best guesses.

I have to be honest, I really don't understand what is all the secrecy is about,
The details and accuracy in answers you get reflects the details you provide about your question.


Good luck.

[quest]

I'm looking for the details myself

when I find them I will post

And yes you are absolutely right---Unless you have details it's kinda like a stab in the dark.

It was never my intention to confuse anybody.

Being a noob I was "assuming" that there was a simple answer and explanation to my original question at the start of the thread.

Now I see that my assumption was incorrect and I stand corrected.

Thank you pointing this out

[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.