Mitsubishi Electric - mnet

[beebarron]

I'm looking to upgrade the control system of our city multi installation. we currently have a PC with MJ310 software and are looking to upgrade to TG2000 on the PC with 4 AG 150.

HOWEVER our existing MNET cabling is 0.75mm and the recommened cable size is 1.2 - 1.5mm.
We have almost 400 indoor units - so recabling would be a complete nightmare. We could re do the cabling from the outdoors to the AG150 units fairly easily.

But mitsubish won't give any guarentees that the mnet will run if its cabled in 0.75mm.

Our present system has never had any transmission errors - but i believe that the AG150 increasesthe data rate quite considerably?

Has anyone had any experience of similar issues? I I cant really justify spending around 20K for a new control system that might not work!!

Also abart from measuring the voltage at the furthest point on the mnet is there any other ways of predicting problems?

A
ny help / advice much apreciated.

[aircool]

i think theres a booster that can be got,will try and find out for you tomorrow.

[Thermatech]

At the moment you have a number of gateways connected to the outdoor units & the gateways are connected to an IFU interface.
The outdoor units communicate with the indoor units & communicate with the gateways via the central control cable daisy chain.
The gateways communicate with the outdoor units & the IFU interface.
The IFU interface communicates with the gateways & the MJ310 PC.

All this has worked for a number of years without communication faults ?


The new installation replaces the gatways with AG150 central controllers.
The central controllers now communicate with the outdoor units & the TG2000.

A major difference is that the central control line from the AG150 is now powered with a power pack which runs on 24v dc instead of the old 30v dc.

Why not try out installing one AG150 as stand alone control system for 50 indoor units for a few weeks & see if it nusance trips on communication faults. Try this on the current gateway which has the longest cable lenght & largest number of outdoor units connected.
You will loose control of these units on the MJ310 during this test & only be able to control via the AG150 but it would prove if communication faults might be a problem.

If one outdoor unit & its indoor units tend to trip on communication faults then an Mnet booster can be fitted in the daisy chain of the indoor units on that system. But this would have been an ongoing problem for your current installation.

A precaution would be to install new control cable daisy chain from the AG150 to the outdoor units which as you indicate would be relatively easy as part of the upgrade.
The main thing is to avoid running the control cables next to power cables & make sure the screen is connected to ground to avoid the comminications being corrupted by external noise.

[beebarron]

hi

thanks for the sound advice. We have never had any problems with transmission errors etc, and the system has been in around 9 years.
Think i will go down the trial route on the units on one gateway.

I was just concerned - as neither Mitzi or the contractor would give any assurances that the system would work. And I would be out of a job if I spent 20K on a system that didn't work!

Only problem is - money is only available to the end of march :( and may not be available next year

Just out of interest - was the 0.75mm cable 'underspec' for a MJ310 installation?

[Thermatech]

Mnet cable specification has always been 1.25 to 1.5mm sheild 2 core cable for the cable going from the outdoor unit to the indoor units & also for the centralized control cable going from the outdoor units back to the gateway or central controller.

The new AG150's will communicate with TG2000 via network cable.
So if as a precaution you replace the central control cable daisy chain from the Ag150 to all the outdoor units then only the Mnet daisy chain from each outdoor unit to its respective indoor units is left with existing 0.75mm cable.
Each outdoor unit suppies the 30v dc Mnet to its connected indoor units & is seperate from the central control Mnet.
If this had been a problem then you would have been having ongoing communication problems over the last 9 years.
As the 30v dc is generated at the outdoor unit this voltage gradually drops the further down the daisy chain as each indoor circuit board & each remote controller drops the voltage very slightly.
The size of cable & the length of the cable has some resistance & therefore some impact on the voltage depending on cable size & length.
So if at the very last indoor unit on the daisy chain you have lets say aprox 25v dc then you might get some intermittent 6607 communication faults.
The outdoor unit / system has to be able to cope with up to 16 indoor units + 16 remote controllers + up to 500m cable length.
If you have a system with only 10 indoor unit + 10 remote controllers + 100m of cable then the resistance & voltage drop will be less than the larger system with excessive cable length.

Whatever the number of indoor units + remote controllers + cable length you have with your systems on site the fact that they have worked without communication faults is proof that the voltage drop is not excessive.

You will now have a new power pack with the AG150 which will now supply the Mnet power to the outdoor units on the central control daisy chain. As the specification is 1.25 to 1.5mm cable it would seem to be a sensible precaution to upgrade this cable to the outdoor units at the same time.

[beebarron]

Thanks again for the advice.

A colleauge has suggested that as I'm going to be using Tg 2000 software there is no need to use AG150's - but simply use GB50 INTERFACES to replace the existing gateways and connect to the PC.

Any thoughts on this?

[Thermatech]

The GB50 option is cheaper but the advantage of using the AG150 is that it provides full backup control.
The GB50 is similare to the AG150 but has no touch screen so you cannot use it as a controller it is just an interface.
So if the PC with your TG2000 has any problem you loose control of all City Multi systems untill you get your PC fixed. But if you also have the AG150's you can still control on the City Multi systems using the AG150's.