Al, here is something to look into. It is a data logging device we intend on using and seems to have all the requirements you are looking for. The web site is heapg.com and the device is the Horner XLE. It has a compact flash unit on it which I think is currently maxed at 2gig. Your choice on the size to use. And in the comming month they are set to release the firm ware which will allow you to remote FTP to the device and pull the data file from the compact flash. Then you could use a simple program to manipulate this CSV file into some other format and you could run a query, should you be using SQL, compare the two and fill in any gaps or missing data. The PLC is easy to program and has plenty of options such as Dial up modem, TCP/IP and Wireless. All the details are on their web page which I gave you above. Just something to look at if your interested.
Have a nice day.
[quote=“AlThePal”]I have looked without much success for a device which I can install in remote locations, primarily to carry out datalogging, but also with the possibility of local control. It will have to be able to log locally to a non-volatile store (in case of local power loss) and send logged data to a central store as required. It will potentially have to cope with holding several days of data before it is emptied.
I read with interest Nathan’s post on reading historical data from a PLC. The only downside I can see is that this depends on PLC memory, which tends to be rather limited/expensive. This might work if a PLC exists than can log (simply!) to CompactFlash media or similar.
We are not keen to use a PC in each remote location due to cost and reliability issues. I would be interested to hear if anyone has found a product which fits the bill.[/quote]