The conventional "industrial solution" to this is to use a Thermocouple or RTD and run that to a "transmitter" which creates a 4-20 ma signal that can be driven long distance to a 4-20 ma input board. Its old technology but it still works in thousands of existing applications. Omega has some cheap transmitters for less than $100, you can pickup a nice stainless temp probe for about $50 on ebay.. but then you need a 4-20ma input on a PLC or PC card etc. If you shop ebay carefully you could probably come up with a complete Thermocouple to PC solution for $100 or so.... but it would require some careful buying.. Shipping might kill that idea. A newer conventional industrial solution is to run your Thermocouple or RTD to a "Hockey Puck" signal conditioner which talks some ethernet protocol, or Modbus RTU etc ... but this is more $. Might be able to pickup a cheap hockey puck device off Ebay..?
Dave On 7/23/2011 12:24 PM, Peter C. Wallace wrote: > On Sat, 23 Jul 2011, gene heskett wrote: > > >> Date: Sat, 23 Jul 2011 11:53:24 -0400 >> From: gene heskett<[email protected]> >> Reply-To: "Enhanced Machine Controller (EMC)" >> <[email protected]> >> To: [email protected] >> Subject: Re: [Emc-users] OT -- Ethernet thermometer? >> >> On Saturday, July 23, 2011 11:33:03 AM Przemek Klosowski did opine: >> >> >>> On Fri, Jul 22, 2011 at 3:15 PM, Igor Chudov<[email protected]> wrote: >>> >>>> El cheapo ethernet routers cost $9.99: >>>> >>>> http://www.newegg.com/Product/Product.aspx?Item=N82E16833166034 >>>> >>>> I believe that a cheap Ethernet thermometer would cost roughly as >>>> much, if someone wanted to produce it. >>>> >>> Yeah but this Rosewill box is really a plastic box with five >>> connectors surrounding a dedicated ethernet switch chip---a mass >>> market item that's cheap because they make zillions. Anything else has >>> volumes that are multiple orders of magnitude smaller. >>> >>> To get a good price, the only way is to judo the strength of the mass >>> market---repurpose an OpenWRT router or a cast-off PC. Even then, >>> however, you need the Ethernet cable AND the power line---unless you >>> jigged the power (low-voltage DC, of course) over the unused pairs in >>> the Ethernet. >>> >>> This gives me an idea--I think it might work to hook one of those >>> two-wire or I2C Dallas/Maxim temp sensors over a long 'ethernet' >>> cable, and bitbang them. Does anyone know what are the practical >>> limitations on I2C/two-wire? A twisted-pair ethernet cable should >>> help... >>> >> Unforch, I2C is not really suited for long distances, the cables >> capacitance limit is 400 pf, it is not a "terminated" transmission line >> design by any stretch. No cat5 type cable has any advantage in its twisted >> pair, differential receiver design. Neither do the std 4 wire phone >> cables. 40 feet and I2C is Dead in the Water. >> >> That isn't saying that a 3 wire circuit, with active pullups that also >> serve as terminators for echo& ringing control, couldn't be made to work >> at 100's of yards, but the thing is going to need about 5 watts of power >> available at both ends of the cable for driver and term power. If flat >> ribbon cable was used, which has an impedance of about 110 ohms, then the >> chips designed for active terms on a scsi bus could be 'borrowed', but for >> other cable types, like 4 wire round or flat telco and cat5 twisted pair >> styles, the term match will not be as close as they will range down to the >> 60 ohms area. One might be reduced to looking at first one end, then the >> other of the circuit and adjusting the terminating R for minimum ringing >> and echo's as seen on a 100 mhz scope. Not practical for a just plug it in >> and its supposed to work, even for folks who have no clue what 'VSWR' >> stands for. >> >> The lesson is to stick with properly terminated twisted pair cabling if any >> distance is involved. >> > Yea. probably a 8 pin PIC or AVR uController with a serial say 9600 baud > RS-422 interface, with power and comm sent on the CAT5 (say double up the 5V > and ground wires) local 3.3V LDO regulator so the cable 5V can droop to 3.3V > without harm and a big cap on the remote 5V so the peak power needed to send a > short packet into the terminated wire (30 mA or so) is supplied by the cap. > This ought to get you to a couple hundred meters. Low average power is > important not just for cable length but to reduce self heating if the > temperature sensor is on board. > > > (a sensor on any kind of Ethernet board will be way above ambient) > > >> Cheers, gene >> -- >> "There are four boxes to be used in defense of liberty: >> soap, ballot, jury, and ammo. Please use in that order." >> -Ed Howdershelt (Author) >> Now is the time for all good men to come to. >> -- Walt Kelly >> >> ------------------------------------------------------------------------------ >> Storage Efficiency Calculator >> This modeling tool is based on patent-pending intellectual property that >> has been used successfully in hundreds of IBM storage optimization engage- >> ments, worldwide. Store less, Store more with what you own, Move data to >> the right place. Try It Now! http://www.accelacomm.com/jaw/sfnl/114/51427378/ >> _______________________________________________ >> Emc-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> > Peter Wallace > Mesa Electronics > > (\__/) > (='.'=) This is Bunny. Copy and paste bunny into your > (")_(") signature to help him gain world domination. > > > ------------------------------------------------------------------------------ > Storage Efficiency Calculator > This modeling tool is based on patent-pending intellectual property that > has been used successfully in hundreds of IBM storage optimization engage- > ments, worldwide. Store less, Store more with what you own, Move data to > the right place. Try It Now! http://www.accelacomm.com/jaw/sfnl/114/51427378/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > > ------------------------------------------------------------------------------ Magic Quadrant for Content-Aware Data Loss Prevention Research study explores the data loss prevention market. Includes in-depth analysis on the changes within the DLP market, and the criteria used to evaluate the strengths and weaknesses of these DLP solutions. http://www.accelacomm.com/jaw/sfnl/114/51385063/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
