HMI with Mobus RTU can run at low temp (-40C)

[TheFox]

Hello, I am working on an application for a customer that will be mounted on a truck outdoors. The problem is that the temperature outside can get as low as -40 degrees celsius (-40F) and although the HMI will be panel mounted the screen will be exposed to the elments (rain, snow, ice, wind). The only other criteria is that the HMI must be able to communicate via Modbus RTU. I have only been able to find panels that work from 0-50C. Anyone have any suggestions. I have found monitors but that is not an option. Thanks in advance.

[TimWilborne]

That's a tough one. Being mobile I guess we can't count on it being powered u all the time?

[Duffanator]

You can check these guys out: http://www.qsicorp.com/ Their stock terminals won't get down to the temperatures you are talking about (they are lower than most) but they do make custom terminals. Perhaps with heaters built in?

[paulengr]

One of the basic problems biting you is the screen itself. If you go with any design that uses an LCD display, it's a liquid crystal. Those are what drives the specs to 0-50C. Below roughly 0 C, the liquid crystal more or less "freezes" (gels) and above that temperature, again the chemistry is such that it just goes opaque. Regardless of this problem, any push buttons that you have tend to have problems with any condensation at all freezing the contacts (and all relays are susceptible to this). Best I could find is that Maple Systems sells a vacuum fluorescent display good to -10 C. At some point it will become difficult to get the gas to ignite, just as with fluorescent tube lighting. If you want to go lower, you'll need to find an LED HMI. An LED itself can go to liquid nitrogen temperatures or better. The controller will become your limiting factor. Checking Uticor (or ezautomation.net), the spec is only good to 0C but I'll bet you can push them well beyond that without any long term issues. In this case, you'll have a display but your inputs will become a factor...but you can probably easily find keypads and such easier than displays. You may also want to check some unconventional sources. Check Digikey, Mouser, Allied Electronics, and Newark for LED display modules themselves. You'll have to provide interfacing (not as convenient as a prepackaged HMI) but at least it will work. Most use some sort of serial interface.

[Rod_Hackney]

Can you go wireless and place the HMI in the cab and the controller on the trailer of the truck? This would allow the HMI to be portable from truck to truck with similar hardware on the trailer.