Temperature readings for a given thermocouple wire will follow a definable curve. Extension grade wire offers a more restricted temperature range than does thermocouple grade wire. The extension wire follows the same temperature curve as the thermocouple wire up to a certain temperature, approximately 400º F, then ceases to follow the EMF/temperature curve for that calibration. If you use extension grade wire beyond its limitations, you may introduce a significantly large error into your readings. For reliable readings, the thermocouple wire in the terminal head must be connected to the same thermocouple type wire (either thermocouple grade or extension grade) all the way to the readout instrumentation. A common scenario is to use copper wire rather than thermocouple or extension wire, but this is not a good idea. Copper does not follow the EMF/temperature curve of the thermocouple at all (with the exception of certain copper alloys as noted below) and therefore introduces a tremendous degree of error. If copper wire is the only option in a given situation, one solution is to install an electronic reference junction in the terminal head or use a "hockey-puck" style transmitter (generally 4-20 mA) at the terminal head. For the base metal industrial thermocouples (Types E, J, T, K and N), the associated extension grade wire is of a metallurgical construction similar to that of thermocouple wire. For refractory metal thermocouples such as Type C (tungsten/5% rhenium vs. tungsten/26% rhenium), it is impractical, from both a cost and technical viewpoint, to run pure tungsten wire, so an alloy wire is used. For the platinum series (R, S and B), Types R & S use a copper/copper Alloy 11. Type B thermocouples are the only type that can use regular copper/copper wire, provided the wire is not exposed to temperatures in excess of 212º F. From 212º F to 392º F, a proprietary wire alloy is available. Reference junction compensation is not a problem with RTDs, because they use resistance instead of millivolts as the measuring signal. The leadwires extending from the INDUSTRIAL RTD element to the terminal post are generally copper or nickel. Proper installation of your sensor assembly can help you avoid many common problems and downtime. With a little care and attention to the installation procedure, a good quality sensor assembly should provide years of reliable operation and accurate readings. 7 www.conaxbuf .conaxbuff conaxbuf@conaxbuff 716-684-4500 Fax: 716-684-7 4-7433 1-800-223-2389 · www.conaxbuf falo.com · conaxbuf@conaxbuf falo.com · 716-684-4500 · Fax: 716-68 4-7433