Welcome to a new Voltlog, today I’m going to be building a precision reference box, using these precision Vishay resistors, they were sent to me for free by Vishay, these are from the VHP100 series and they are the ducks guts when it comes to resistors. They have incredible stability, across the entire range of -55 up to +125 degrees Celsius they will vary less than 60ppm. So as you can see they had to define the number over the entire temperature range because if they would have done it traditionally per degree C the number would have been essentially 0.
These are built using a special technology called bulk metal foil, wrapped on a ceramic substrate. Then the assembly is suspended in oil and hermetically sealed in this metal can, thus it’s immune to humidity changes. Every one of these resistors is basically custom made so you can order them in any value, but as expected they don’t come cheap. Purchasing these in some standard values carried at the big distributor will cost you around $70 a piece.