Resistance Measurement of the 4 mil SS Wire --------------------------------------------- Original Rev. 6-APR-2006 Current Rev. 19-APR-2006 This note is a report on the resistance measurements of the stainless steel wire that is used in the long wire test setup in Lab 8. The resistance measurements were actually made at MSU on samples of the Fort Wayne Metals 4 mil 304V stainless steel wire which were obtained from Fermilab. A careful set of 4 lead resistance measurements was made on March 31 and April 1. The sample being measured was about 2 meters long. It was loosely wound on a threaded cpvc spool and measurements were made at room temperature and at LN2 temperature. After this set of measurements the sample of wire was stress relief heat treated and its resistance was measured again at room temperature and LN2 temperature on April 17 and 18. The results are: Resistance before stress relief Room Temp 123.8 Ohm/m LN2 Temp 110.5 Ohm/m heat treatment Resistance after stress relief Room Temp 105.1 Ohm/m LN2 Temp 90.1 Ohm/m heat treatment Resistance based on the FWM specified 95.8 Ohm/m bulk resistivity of 720 micro Ohm - mm and a 3.85 mil diameter wire Notes: - For each measurement I cycled between room temp and LN2 temp 3 times looking for hysteresis or a permanent shift in the resistance at either temperature. At the 0.05% level I do not see any effects of that type. - The Ohms/meter number above for LN2 temperature does not take into consideration the change in length of the wire going from room temp to LN2 temp. I.E. I measured the resistance of the same physical piece of wire at both temperatures but only measured its length at room temp. - The heat treatment lasted for 24.5 hours at 397 C in a quarts tube with a flow of Helium gas through the tube. At the end of this time the furnace was turned off and allowed to cool at its natural rate while the Helium gas flow was maintained. - As one would expect the resistance ratio (room temp resistance divided by cold resistance) increased a little bit after the heat treatment. Resistance ratio before the heat treatment was 1.121 and after heat treatment it is 1.166 - The accuracy of the above numbers is limited by my ability to measure the length of the wire between the potential leads. The sample is over 2 meters long and I estimate that I can measure its length to 2mm. - I verified that the sample was not under tension stress in the sample holder when it was at LN2 temp. - A previous note said that this 4 mil Fort Wayne Metals wire from Fermi is actually 3.85 mil in diameter. I have not checked the diameter of this sample at that level of accuracy. - These measurements were made with the Fluke 8505A meter which was checked with the General Radio and Leads and Northrup standard resistors at: 10 Ohm, 100 Ohm, and 1000 Ohm. - The room temperature was between 22 and 23 C for the set of measurements before stress relief heat treatment. For the set of measurements after the heat treatment the room temperature was between 21 and 22 C. These measured values are considerably higher than what was expected. On their web site the supplier of the wire, Fort Wayne Metals, gives the bulk resistivity of the wire as: 720 uOhm-mm. See: www.fwmetals.com/resources_specsheets/304v.pdf For the specified 4 mil diameter of the wire (0.0508 mm radius) the bulk resistivity value from Fort Wayne Metals implies that we should have expected a resistance per meter of 88.8 Ohms/meter. As shown above we measured 123.8 Ohms/meter Part of this difference may be due to the "4 mil" wire only measuring 3.85 mil diameter as reported by Doug. A 3.85 mil diameter wire with the bulk resistivity given by Fort Wayne Metals would have a resistance of 95.8 Ohms/meter but that still does not match what we measured. In the information on their web site, Fort Wayne Metals talks about using a stress relieving heat treatment on their 304V wire. "Thermal Treatment In wire form, 304V will gain tensile strength when stress relieved at 350-427 C. A reducing atmosphere is preferred but inert gas can be used. 304V will fully anneal at 1010-1121 C in just a few minutes. There is a carbide precipitation phenomenon that occurs between 427 and 899 C that reduces the corrosion resistance of the alloy. American Society for Testing Materials has described a test method to ensure the alloy has not been damaged."