Hi Jan My rig is a slow control-loop DC source (settings from 41.2 to 64.5V, depending on t/c type and wire gauge/length) into a RC net (two large caps), that upon start of discharge, open a mercury switch between source and caps. The welding "electrode" is an Al block.
I was not able to get consistent results using a C block. What is your set-up ? Brian -----Original Message----- From: Mobers Jan (ST-VS/ENG1) [ mailto:[email protected]] Sent: Wednesday, April 28, 2004 6:35 AM To: [email protected] Subject: RE: thermocouples Hello Brian, You mentioned that you welding the thermocouples by yourself. Please can you explain how do you do welding the thermocouples. I do this with a DC loaded Capacitor and a carbon bar. Best Regards Jan Mobers -----Original Message----- From: [email protected] [ mailto:[email protected]]On Behalf Of Brian O'Connell Sent: 2004 apr 28 15:09 To: [email protected] Subject: RE: thermocouples An error from IEEE, so try again. Empirical measurements using type T and K thermocouples, welded in inert noble (argon) gas, as read by an HP 34970, and compared to thermocouple junctions formed by mechanical twist, solder, and ambient-air weld; and buried in separate wells, approx 1cm depth x 2.1mm width, in an extruded Al bar, where temperature dwells were at -10 and +75 C, at 28% RH, each dwell period = 2.5 hours. For the initial 28 hours of operations, peak diff, between all thermocouples was 0.7C, after which the twisted t/c junctions became erratic. The experiment ran for approx 100 hrs. If the twisted t/c junctions are ignored, peak diff for the duration of the test was 0.9C, which resulted from a difference in response time between the soldered and welded thermocouples, between dwells. And because I weld a fresh set of thermocouples for each series of product safety Type Tests, I do not consider oxidation to contribute to error, and I do not consider it in my uncertainty calcs. I cannot justify the time and expense of welding in argon envelope; but I do attempt to perform precise and consistent welds. luck, Brian
