Looking at ways to optimize GPS-Rb-OCXO performance, using dewar, foam and fan cooling, using a fan was an eye opener. I have now come to the conclusion that for the temperature environment we are working in, a fan is the best way for all three. I am using a 5X5X1 cm fan drawing 50 mA at 12 Volt, results are amazing. Realizing that Tbolt and Rb's have to be cooled not heated I powered up a FRS with out heat sink and monitored the back plate. With 22 C ambient it increased on the bench to 58 C. Placing the fan 5 cm away, the temperature dropped to 38.9 C in 2.5 minutes! I repeated the test using a laptop heat pipe with the fan running at 5 Volt and 170 mA the back plate temperature dropped to 30 C. Presently running a HP 10811 with similar results. I am convinced that I will be able to get better than .1 C control in all three applications. Having large temp. fluctuations outside this time of the year I will take advantage of the large fluctuations. I think the challenge will be at higher ambient's, it will determine the set point. Right now I am looking at the 40 to 45 C range. A small amount of air flow goes a long way. Noise and vibration is small and manageable. Any comments? Fan power is lower than heating how ever all three devices power consumption is increased overcoming the lower case temp. Bert Kehren In a message dated 1/18/2011 6:42:29 A.M. Eastern Standard Time, hol...@hotmail.com writes:
Generally you have to do some playing with the fan position and internal baffling and thermal mass for best performance of the temperature controller. You don't want direct airflow onto the tbolt. Also you probably don't want an large/aggressive fan... a little airflow can go a long way. Some thermal mass can be useful... I use a 2 kg stainless steel calibration weight (but probably need to do some testing without it. Warren's setup seems to be a little better than mine, but he probably does not need to deal with the heating/air conditioning extremes that I do) One thing that I have is an ESI SR104 hyper-accurate 10K resistance standard. These have two temperatures where their resistance is exactly 10K. I have it (and a Fluke 732B 10V precision voltage reference) mounted in a box with a tbolt set to one of those temperatures... cheap temperature controlled cal lab in a cardboard box. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.