PDA

View Full Version : twin wire with shielded cable







question mark
08-03-2013, 07:14 AM
hi masters,
i have been involved in many small install for split ducted of Fujitsu and mainly Mitsubishi , but always got stuck on thinking that how a twin wire and shielded cable controls heating and cooling, fan speed, timers delay and all this stuff i can understand it in three or more wires but how does it do in just to wires.
Thanks :cool:

Tesla
08-03-2013, 08:13 AM
Hi ?
It's all done with zero's and one's with, search it - LAN or LON. Most companies at the mo have propriety code which is slightly changed from the standard so they can screw customers for more money cause it costs a lot of dollars to write the code. There are intermediate codes which read the propriety and convert it to the standards like Tridium, OPC and Bacnet for another fee of course - it costs money to write code. There are different levels of complication of these codes ranging from basic binary, asci, machine, hex, c... going up to GUI but it all starts with binary. Then there is serial and parallel where serial would be something like two wires and parallel would be something like 8 wires, with a few one wire. It's all comms at the end of the day and a way to transmit data from one to another. Right now my laptop is using ASCI from the key board then going up a few levels to get it over the net. Very interesting stuff for me an boring for others. Today I was on a job specified for lan and thinking about the hassle of running the cables I thought it would have been easier and cheaper to do it with no wires wireless. This is post 1000 for me and a good question to answer. I normally deal with BMS for HVAC and just love it.

Frikkie
08-03-2013, 08:40 PM
I think Tesla is right, it is digital communications. I always wondered why they use a separate comms cable, why not send the comms across the power cable. If they did then you would only need the power cable between the inside unit and the outside unit which would make an easier installation.

al
08-03-2013, 09:15 PM
Tesla

Is there any commonality across the brands for indoor/outdoor comms? ie a common on/off signal or transmission? i do have a sneaky ulterior motive for asking:)

alec

install monkey
08-03-2013, 09:20 PM
al u cant use any controller to switch them hitatchi's- dodgy git- fit a contactor to kill indoor supplies if you want to stop systems:D

Tesla

Is there any commonality across the brands for indoor/outdoor comms? ie a common on/off signal or transmission? i do have a sneaky ulterior motive for asking:)

alec

al
08-03-2013, 09:56 PM
Stop stalking me you!! You'd be assuming the indoors had seperate power supplies!!

alec

Tesla
09-03-2013, 05:23 AM
Hi guys
First up this topic should be in the controls section.
Frikkie You are right, we can and do on some systems send data over power. In NZ some domestic hot water systems switch off and on from signals an the power line, called the ripple system. Not sure why we don't use it more in controls. I am working on a new system using the Arduino controller and will try to incorporate this function to save wiring - the idea is to use smart sensors and all I/O so as to communicate to blocks and sub blocks with LAN (not sending out 0 - 10v) but communicating to an address and sub address with data. Have become very busy at work though
Hi Al with most newer units of the same brand will either have a lon (echlon) chip on the controls board or lan for such a purpose to communicate off/on and a limited amount of other points. Here you can daisy chain a bunch of units on site and connect them up to a HLI like tridium, opc which can then relay this data to a BMS. I only know of one person who has done it.

al
09-03-2013, 07:15 PM
Hi Tesla

I'm not as schooled as i would wish to be on controls, i've asked a guy who has developed a system for elliwell/dixell/carel etc, he got their code and has developed an interface that works with nearly all brands, i'm hoping to trial one soon. He took some info and said the same as yourself, it will mean getting into the board infrastructure.

The Arduino looks interesting, how do you physically pick up the signals off the mains voltage, do you connect 230v to the board or use the magnetic field?

BTW might be best to relocate this to the controls section alright:)

alec

Tesla
09-03-2013, 08:07 PM
Hi Al
Interesting subject here code breaking. Pretty simple stuff as at the end of the day they all use zero's and one's, and they all use generic chips except some military applications. Like the tridium tunnels into the ports, reads and writes to them. Others use higher level language which is faster. All you need is a bigger chip to read the ports of another chip and decipher the data which is either data, addresses or control just like a computer. They even have devices that can read a comms cable from withing a meter away and that was available 15 years ago. The higher level languages allow us to read letters and use graphics or now (ten years ago) speach to text and vice versa. Any thing is possible. This will all be old hack very soon when we get into photon as opposed to electron devices.
Yes we would use emr for reading on the Arduino over power, but that's not the only way we can use voltage spikes say on a 240v and send a spike of low power at say 500v, or for reading another chip it could be like using a voltage meter with high impedance to measure with. You can buy devices that send eithernet over 240v belkin and others have them for domestic purposes but we could use them with 24v in a commercial system. In the not too far past proprietary companies held the customers to randsome with what ever prices they wanted to charge and the only other choice was another system that would do the same at the cost of replacing costly systems.

question mark
12-03-2013, 09:02 AM
Hi mate
nice to be a part of your 1000th post , thanks for the very comprehensive answer , something for me to learn in near future.
thanks a lot

Frikkie
12-03-2013, 07:34 PM
You can buy devices that send eithernet over 240v belkin and others have them for domestic purposes but we could use them with 24v in a commercial system.

I guess part of the problem with using data over power networks is the crossing of the trade skills. Data people like to work with low voltages (ELV) and electrical people don't like to work with data. It would be a new breed of tradesman that would work with data over LV and MV electrical networks.

Tesla
13-03-2013, 07:10 AM
Yeah Frikkie that would probably leave it to us smarter Fridgies Haha.

Frikkie
13-03-2013, 09:13 PM
We farmers are also pretty smart (sometimes), if you need repairs quickly and with only a hammer and a screwdriver you definatey need a farmer ;)

alexhk
02-04-2013, 06:25 AM
Hi Guys,

I've been redirected here by one of Tesla's helpful posts to a question of mine. A bit pressed for time today but will come back later.

What I wanted to say is that you should look into the Bus Pirate if you want to hack and use these 2 wire (or other protocols0. It's very inexpensive but you really need to have a lot of time on hand with programming/comm experience etc. It basically lets you listen and talk to all your devices.

http://dangerousprototypes.com/docs/Bus_Pirate

Can be purchased for less than $30:
http://www.seeedstudio.com/depot/bus-pirate-v3-assembled-p-609.html?cPath=61_68

They just released a new version (v4) which is not yet fully supported, so V3.5 is still the best choice IMHO.

RusBuka
02-04-2013, 08:51 AM
Ahahaha...if you hack MHI, ME or General (lon) type there )))

Tesla
02-04-2013, 12:24 PM
Thanks alexhk
I should point out my direction here before some people get the wrong idea. The purpose of using the two wire for power and comms is to save on install costs. Not really to spy on other systems but I wouldn't want to eliminate that idea either.
an example is we have a typical office block floor with around 30 temp sensors spread around. With dumb sensors we will have to wire each sensor back to the controller. With smart sensors we could simplify it with two circles of wires one for a centre zone and one for a perimeter zone. This would reduce the amount of cable required and a huge amount of labor to install the cable. This would also allow for some wireless sensors in the circuit for hard to cable places like very high places. The networks would not only serve for temp sensors but also for the likes of VAV actuators with power and signal.
I am guessing that a 24VAC grounded neutral for power could be used with a RS485 signal communicated on that same wire with opto isolators to prevent the power getting into the controller. Looking at using the Arduino controller as it is open source and cheap.
This move could take the power away from the big boys in the controls arena and provide a cheaper product for the customer. The only security on the system could be an access password which the customer would own to prevent outside hacking.
Direction would be appreciated...

alexhk
03-04-2013, 01:20 AM
I am surprised that there is no community of refrigerant engineers who puts the information about technologies/protocols used online for everyone else to see. On our big Daikin ACs the (wall mounted) remotes are on a simple cable, I guess putting a Bus Pirate in between would tell me exactly what I need to know in order to control the air conditions via computer for instance.


an example is we have a typical office block floor with around 30 temp sensors spread around. With dumb sensors we will have to wire each sensor back to the controller. With smart sensors we could simplify it with two circles of wires one for a centre zone and one for a perimeter zone. This would reduce the amount of cable required and a huge amount of labor to install the cable.

Have a look a the DS18B20, it sounds almost exactly what you need. It's very popular with Arduino folks too and I am also using it for a couple of things (although not on Arduino which we don't really use in my field).

http://datasheets.maximintegrated.com/en/ds/DS18B20.pdf

I am not sure about the 24V, but it does have what they call a "parasite mode" so you can run it on a line that actually has some other purpose. I guess the easiest would be to buy a few of them and get your Arduino ready and play around with it for a while.

Basically you have a single wire and drop as many sensors as you want, at different locations. They all have their own ID so you can simply request the temperature or "ping" them to get a list of all sensors in the 'network'. Very easy. There are also boxes with RS485 to which you can connect this simply 1 wire network or even get info wireless. If you google Arduino DS18B20 you'll also find lots of info (hopefully not telling you something you already know).

Instead of buying the sensor components, we get them ready made from China, very cheap. Basically they just put them in small aluminum tubes, water proof hem with epoxy, and cut cable/wires to length. saves a lot of hassle.

Looks like this:
http://item.taobao.com/item.htm?spm=a230r.1.14.129.mwXzR5&id=5237873596
(didn't use that company, just first search result on Taobao which is the Chinese eBay)

I have them connected to a ControlByWeb device (not what you are looking for by I post it anyway):
https://www.controlbyweb.com/x300/

They also work with the CAI WebControl, which I bought on Amazon for just under $40 but I didn't try that yet.
http://www.redhillnetworks.com/products/webcontrol/

Both of them have a limited number of sensors compared to putting something together by yourself. You could also put a simple 1-wire / 2-wire network together with a small PC (or Rasperry Pi or something small like that), I'll see if I can find the links I had found a couple of months ago.

My requirement for using them (and the "PLCs") is different than yours, but maybe you can use some of that info). I didn't use Ardiuno because of time constraints and because I've been told they don't communicate reliable over Ethernet. Reliability might be an issue.

Tesla
03-04-2013, 10:27 AM
Thanks Alexhk
That's a lot of info to decipher. The sensors at top look good for 5volts. You are right about the reliability with the Arduino looking at the surface mount solder job on mine - I wonder how long it will last. Yes the last two devices are no good with very limited points as some BMS could have 50,000 points. My Chinese is a little rusty for the second link lol. I have finally got a Samsung Note 2 and hope to be using it to communicate to various systems - yes from HK for 25% less than retail in Ausie. Shocking how we pay more for this sort of stuff.

alexhk
04-04-2013, 01:11 AM
If I am not wrong 6V is the max for a differential RS485 wire pair, so it seems that the DS18B20 would work very well on a RS485 wire pair. If you actually don't need that RS485 to go where the sensors are, you could just build a dedicated wire pair just for that. Or use a 3 wire cable (+, -, data) just for that. Beats connecting all sensors to the "homebase' any time.

What do you normally connect these sensors to? I assume that's some closed system by a fixed vendor? And it gathers the temperatures and then controls the air conditions and fans?

Tesla
05-04-2013, 12:24 AM
Yes it all goes back to home base what ever type of temp sensor it is. I would not want to limit the comms system to just sensors though, I would like to use it for outputs too. Using smart output boards where a signal is sent to it and it will latch or remember that signal and hold say a valve at that signal position. I think we can get up to about 4 kilometers on rs485 and HVAC controls do not need speed. That's why I was going for a 24vac two wire system using opto's at the controller. Big risk is someone shorting out the 24v wires whilst doing some live wireing which we do all the time. I am thinking there must be a way to overlay the rs485 signal onto the 24v power then pick it up from a mini sensor like a volt stick has (just a real fast one). And of course an easy way to put it back on (write). Best I think by interupting the signal. Or am I simply very confused?

assailant
30-06-2013, 07:29 AM
Hi guys
Frikkie You are right, we can and do on some systems send data over power.

hitachi 2.5 and 3.5kW wall splits only use a 2 wire 35VDC interconnecting for power and comms between indoor and outdoor unit.