The LM317s arrived. Now I have to characterize them. The tabs are the outputs so I've ordered nylon threaded hex spacers to assist in mounting them.
I have a nice 20 V 5 A linear lab supply to feed the parts and a precision voltage reference and op amp to drive the Vctl pins and the metering system. And a suitable means of controlling the environment.
I've got 5x 44421/2A relay cards and a 3457A. Inclination is to use an ATMega to drive the relay cards via GPIB along with the 3457A. At NPLC 10 the 3457A will read each device twice a minute at 7.5 digits in MATH HI-RES mode. 15 mV seems a good choice of reference voltage as that will put the 3457A mid range on its lowest scale.
I've been wrestling with the how to measure thermal stability. A circulating system with a set of Peltier devices and lots of thermal sensors and muffin fans seems a start.
I just cut a pair of 83 mm squares of 0.200" aluminum which I'll glue with thermal cement to opposite sides of four 40 mm Peltier junctions which will in turn be attached to large heatsinks. The plates are because the heatsinks are only 70 mm wide. It should improve transfer from the Peltier device to the heatsinks. That will let me measure them heating and cooling just by reversing the Peltier polarity. A hot loop and a cold loop. Muffin fan apiece. There's no need for strength, so roof flashing will serve for ductwork. Foil face foam insulation mounted at the corners inside a large box with batting to suppress air currents.
I built a triple stacked junction device with a CPU fan. It will hit freezing in seconds. That's part of a more elaborate version of this environmental test setup.
The relevant question is what are the "ideal" parameters? I have no clue at this point other than simple stability over time and temperature. That may be it. Pick pairs which have best lab environment stability.
Have Fun!
Reg
