Temperature Sensors Information Request

- Which are the basic temperature sensor types ? - How they work (physics principle) ? - Which are their differences from a performance point of view ? - Is there a “better” type ? - How they differ electronically ? - Which are the standards for temperature signals ? - How many signals are usually required for a sensor ? - Do they need to be calibrated “often” ? - Which ranges and resolutions are standard and which are considered “high” ? - Are there special sensors for cryogenics ? - Are there special sensors for very high temperatures? - Are there standard “profiles” for sensors connected to a fieldbus (CAN, Profibus, AS-interface, ...) ? - Are there “must-know” sensor manufacturers ? - Any tutorials on-line ? - What I’m missing ? ;-) Thanks in advance for your time.

Brian T. Smith

Marty: Here are some web links to address some of your questions: http://www.isa.org/~sarni/temper.htm http://www.isa.org/~sarni/rtd.htm Check web sites of manufacturers of temperature sensors. http://www.isadirectory.org/online/master.cfm?Letter=T look at the various catagories of temperature sensors. Brian T. Smith, C.E.T. Nova Chemicals(Canada)Ltd., Sarnia, ON. Canada. (519)332-1212 x7920, Fax:(519)339-7301. Opinions expressed are those of the author and not necessarily those of NOVA Chemicals. Personal home page: http://www.xcelco.on.ca/~btsmith/

Johan Bengtsson

Some of the physics: The two most comonly used ought to be pt100 and thermocouple. P100 is a platinium wire with the resistance 100 ohm at 0 degrees celsius. The resistance changes with temperature. If the wire is too long it can be connected with 3, or even better 4 wires. The idea behind this is to compensate for the extra resistance of the wires. P100 sensors can be used in the range -260 to 630 degrees celsius. Temocouple is two pieces of different metals connected together and works because of something called the Seebeck effect. What is really happening is a voltage is generated between the two pieces of metal depending on temperature and this voltage difference is then carried thru the special cable (each wire of the same metal as it was originally connected to) and measured at some other place. Originally you had to have a known reference temperature at the measuring site (for example a mix of ice and water = 0 degrees celsius), today that is taken care of in other ways. The thermocouples are in several types with different combination of metals. Type K can be used in the range -155 to 1375 degrees celsius This is the answer to some of your questions, I ask for others to fill in the rest...
Temperature sensors:
Please come back in few days. I will give you a concise, technical nearly savant tutorial, all supported by references. This coming résumé will be several pages long. The subject is so intense that I'm not going to check what to complement from the referenced web sites.

Jane Rowsell

Have you considered fibre optic temperature sensors? These give real time, continuous monitoring, for cryogenic temperatures up to 350C. They are not affected by EMI. Visit www.yorksensors.com , with apologies for the quality of the website, it is being improved!