After fielding over 1000 UV monitors over a span of 10 years using this part, we began to see that the output voltage of some of the monitors, used in the same circuit made by the same vendor, became unstable over a relatively short period of time.
There are two distinct modes for this instability. The first mode is that, with a very stable light input, the output voltage increases rapidly to as much as 2-3 times the initial voltage over a period of less than 10 minutes. The second mode is that, using the same very stable light input, the output voltage drifts higher by about 10-15% over the course of a few days. We tested and calibrated all 1000+ units we have fielded with the exact same hardware we used when we saw these two modes.
We have seen 3 out of 20 of our most recent build exhibit the first instability mode, and 10 of that same 20 exhibit the second instability mode. We have done several experiments to parse out the source of these instabilities, and those experiments all point to the OPT301M as the most likely cause of the problem. We would like to understand what, if anything, has changed in the manufacture of these parts, and would like your help in developing a solution for the problem we are seeing. The lot numbers (taken from the part itself) from the 3 with the first instability mode are: (2) 75S1KG8 and (1) 65S1T58. Please feel free to contact us for more information or to discuss this with us. Thanks in advance for your help.
