An investigation of the stability of thermistors

In order to beller characterize thermi stors, a group of 405 bead-in-glass and di sc thermi stors were aged in constant tempe rature baths.Samples of 135 thermistors were aged in eac h of three consta nt temperatu re baths held at 0, 30, a nd 60 0c.Eac h sample was composed of 65 bead-in-glass and 70 disc the rmi stors whi ch represented a total of six manufacturers and s ix resistance values.The the rmi stors were maintained at tempe rature for 550 to 770 days and their resistances and the bath te mperatures were periodically moni tored.Analysi s of the data re vealed systematic differe nces between bead-i n-glass a nd di sc the rmi stors upon age ing and indicated a depende nce of age in g behavior on bath tempe rature and resistance value.Drift ra tes wi th in groups of thermistors from eac h manufacture r were fairly uniform .Large initi al c ha nges in the drift rate fo r the di sc thermi stors at 30 and 60 °C (and to a muc h lesser exte nt in the bead-in-glass thermi stors) req uire that thermi stors for use at a n accuracy level of a few te ns of millikelvin s be aged prior to use.