Hi Paul, I assume all references to temperatures in your mail are degree F, if so I am surprised that it causes a problem. I use 27 DS1820's on my system which includes 7 measuring solar panels, these can and have gone to over 120 degrees C and I have not experienced the problems that you have.
How are you detecting the errors? I poll as fast as I can, which is about 15 seconds or so. I log when I get a good read from each device, so error detection is really not had a good read for > 45 seconds. I have a couple of sensors that I suspect are faulty and fail from time to time but the rest are fine and nothing seems to be temperature related. If you have some other way to log errors I would be happy to try to incorporate that into my system to gather more info. Cheers Mick On 29/04/15 01:04, Paul W Panish wrote: > I’m wondering if anyone has information on an issue I’ve been having > with DS18B20 temperature sensors. > > For some time I’ve been developing a wood fired boiler/heating/DHW > system controller > (https://sourceforge.net/projects/bctl/?source=directory) using the > owcapi for all sensing and I/O functionality. My 1-wire network is > limited in length and low in device weight. I have two DS18B20 > temperature sensors and three Hobbyboards DS2408 based PIO boards on a > roughly 50 foot linear topology bus using CAT5e cabling and standard > RJ45 connectors for daisy-chaining bus segments and device attachment. > The drops to each device are 1 meter or less. I’m providing power and > ground through the CAT5e cabling. > > My problem is that there seems to be a strong temperature dependency for > bus read/write errors caused by the DS18B20 sensors. I’ve replaced the > sensors a few times with devices purchased at different times and from > different vendors to rule out random bad devices. > > I’m using a polling loop to read the DS18B20’s and PIO inputs at 5 > second intervals with a conversion resolution of 10 bits > (temperature10). When the system is cold (<140 degrees F) it can go > forever (months) with no errors indicated in any device access. However, > when I fire the boiler I start seeing access errors (file not found) as > the boiler temperature rises above roughly 150 degrees. The error rate > increases as temperatures rise to a maximum level of about 185 degrees > at which point they are quite severe. > > The errors are not just on access to the temperature sensors (which are > hot), but also on access to the DS2408 devices (which remain at room > temperature), though much less frequently. From this I’m deducing that > bus timing is changing for the temperature sensors in such a manner that > they are corrupting access to other devices. I don’t have a scope so I’m > unable to check for slew rates, noise, or reflection problems, however > none of these should be affected by device heating (well maybe slew rate…) > > I’ve implemented a redundant read mechanism (in addition to any > redundancy owfs implements), which has made the system usable, but over > the long term this is a risky solution. I can tolerate the read errors > assuming I get an occasional success, however if a write to a PIO output > is dropped the results could be messy. > > One solution would be to switch to thermocouple sensors for the high > temperature components, using the MAX31850 devices, which I’ll do in the > absence of any other remedy. However, the temperatures I’m dealing with > are all well within the specified limits of the DS18B50 family of > devices, so I’m wondering if anyone has had similar experience and could > shed some light on the situation. > > > ------------------------------------------------------------------------------ > One dashboard for servers and applications across Physical-Virtual-Cloud > Widest out-of-the-box monitoring support with 50+ applications > Performance metrics, stats and reports that give you Actionable Insights > Deep dive visibility with transaction tracing using APM Insight. > http://ad.doubleclick.net/ddm/clk/290420510;117567292;y > _______________________________________________ > Owfs-developers mailing list > Owfs-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------------ One dashboard for servers and applications across Physical-Virtual-Cloud Widest out-of-the-box monitoring support with 50+ applications Performance metrics, stats and reports that give you Actionable Insights Deep dive visibility with transaction tracing using APM Insight. http://ad.doubleclick.net/ddm/clk/290420510;117567292;y _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
