adccommunitymod (AutomationDirect) asked a question.
Created Date: February 06,2009
Created By: DuctSoup
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I'm looking for an inexpensive way to integrate a Davis weather station with a building automation system. The station has a serial proprietary protocol that's published and pretty straightforward. Wondering if I can use a CLICK with port 1 configured as a MODBUS slave and port 2 would be configured for ASCII and connected to the station. Browsing the docs on both sides it's looking feasible but I haven't used CLICK before and was hoping somebody with experience could give me a little programming insight. It looks pretty easy to setup a text string and send it. What I'll get back is a packet with the current sensor readings (various length signed integers and integer constants) with a CRC word at the end. How difficult is it going to be unpack that text string and map it into floating point registers for MODBUS? TIA, Craig
Created Date: February 06,2009
Created by: bcarlton
It sounds like a fun project. The CLICK is so new that you will probably become the defacto expert. The interpretion of the received string is probably going to be character by character. If you can give a link to the Davis protocol info we may be able to help but you'll be doing the majority of the research.
Created Date: February 07,2009
Created by: DuctSoup
Definitely one of the more interesting aspects of the project. If you need to keep track of more than just outside temperature it's hard to beat the bang for the buck you get with Davis ' products. The protocol for the Vantage Pro 2 is here.
http://www.davisnet.com/support/weather/software_dllsdk.asp
It's just a question of the programming mechanics of how you'd choose certain groups of bytes, scale and store them in the MODBUS registers. The Unpack Copy instruction looks promising (as do interrupts).
Created Date: February 07,2009
Created by: bcarlton
With all that protocol support in the DLL then why use a PLC as converter. Why not just use Visual Basic Express (its free from Microsoft) and gather the data from a PC?
Created Date: February 08,2009
Created by: DuctSoup
Reliability, service life, cost ... mostly.
Created Date: February 09,2009
Created by: Kristjan H
I have integrated a Campbell Scientific weather station into a building management system. It was easy with their OPC server, and it allowed me a direct connection between weather station and PC. http://www.campbellsci.com/pc-opc . Their OPC server works OK but it still has room for improvement.
I am betting on OPC to be the future format for data aggregation from different sources.
Created Date: February 09,2009
Created by: DuctSoup
Interesting. What was the end use of the weather information?
In this application I 've got ten big air handlers from different manufacturers to coordinate and schedule. Most are building integrated solar and three are conventional gas fired air rotation units used for secondary destratification and emergency backup heat (that's been handy here the last couple weeks). Problem is they 're all designed as stand alone systems and at times their behaviors conflict so we need objective weather data to anticipate and arbitrate.
On the CLICK front, installed the first one for a different purpose at this site over the weekend. Powered up and running, no problems out of the box. This is one of the reasons I really like the Koyo products.
Created Date: February 09,2009
Created by: Kristjan H
The weather information was just for display and data logging (temperature, wind speed, wind direction etc.) and that is a simple non-critical setup that only requires data polling from the weather station.
You could also use the information for control but this will become a more critical setup. You could have the PC bridge data from one OPC source (weather station) to another (PLC) but I understand your concern with reliability. You can setup a redundant system to address reliability but then the system price goes way up.
Created Date: February 09,2009
Created by: krak
I have to wonder if there is a web site that you could pull local weather conditions from to help with this project?
Created Date: February 09,2009
Created by: DuctSoup
Aside from the whole PC in the loop issue, think Springfield. The best weather data comes from a nearby local airport. Unfortunately, there's a power station complete with it's own little micro climate between the site and the airport. :cool:
Created Date: February 10,2009
Created by: Kristjan H
krak, there is actually a product that allows you to pull real time weather data over the internet. Check out KepWare's Weather Bug: http://www.kepware.com/Spec_Sheets/WeatherBug_Driver.htm . The KepWare stuff is top class.