Quoting "Chaoua, Rashid" : > Hi, > > I have problem reading accurate temperatures using thermocouples. I have > a 40' long refrigerator divided into 4 compartments (3 rooms used for > testing and the fourth houses my electronics). In each room I have a > thermocouple suspended from the ceiling to mid-height of the room. These > thermocouples are connected via thermocouple extension wire to a > National Instruments cFP-1804 module and connected to an isothermal > connector block. Additionally, each room is kept at different > temperatures (ie- room 1: -10C, room 2: -15C, room 3: -20C, room 4: > -30C) and the wire is terminated in the coldest room (room 4). > > > > My problem is as rooms 1-3 are heated up (via heaters) the temperatures > read are incorrect. If I read the temperatures at the thermocouple > directly they read the correct room temperature. When I read the > temperature at the end of the thermocouple extension wire it reads a > much colder temperature (I am using a handheld meter). The same problem > occurs when I use my National Instrument device. I need the temperatures > read to be accurate (I have a program that uses these temperatures to > make a series of decisions) but am unable to find out why I am having > such problems. Can anyone out there lend there expertise? > > Rachid One of the most common errors, perhaps unbelievably, is reversed extension wire which will yield an error of (roughly) double the difference in temperature between the two ends of the extension. It's aided by the silly US color code for T/C wire. Best regards, Spehro Pefhany Thanks for the reply. I already checked the extension wire to make sure they were not reversed. Everything seems to be installed properly. Yet, I get this inaccurate readings still?!?! Rachid -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist