I have done quite a bit of work replacing fans in old equipment with modern fans. I have never seen a case where replacing a hurricane level fan with a whisper quiet fan made any real difference in the cooling inside the unit... typically one sees less than +/- 5C difference anywhere inside the box. Some places get a bit cooler and some a bit warmer. Since most test equipment is speced for industrial temperature ranges and is now used in nice cushy offices and homes any difference is still well within specs.
A few hints... just a little air flow goes a long way in maintaining the cool. Fans that blow in to the chassis are usually more effective than those that exhaust the air out (and overall dust level in the box does not change). The best determining factor for fan noise (other than listening) is the rated current draw. If you can operate the fan a couple of volts below its rating, all the better. Adding 150-200mA of draw to a 12V supply in something like the HP5370 is negligible (the unit was designed to accommodate a couple of extra cards in the chassis). Sometimes it is necessary to add a separate power supply for the fan. In my HP 5371A's I mounted a small wall wart type unit in the box. One thing to be aware of when replacing a 120V fan with a DC fan is the possibility of overheating if the power supply driving the fan goes bad and there are other supplies running in the chassis. The Tek TM5000 series boxes have a thermoswitch that kills AC power to the unit if it gets too hot. Another thing to be aware of is the possibility of the fan supply not being compatible with the line voltage if the unit is shipped overseas. I use a universal input wall wart. Speaking of turbulence and noise, the noise produced by a turbulent air flow increases at the eighth power of the velocity! The HP16500 logic analyzers have two 12V/700mA fans mounted at 90 degrees to each other. The resulting mix can produce a noise level approaching OSHA limits. I replace them with 200mA units and they are then quiet enough to sleep by. _________________________________________________________________ Hotmail® goes with you. http://windowslive.com/Tutorial/Hotmail/Mobile?ocid=TXT_TAGLM_WL_HM_Tutorial_Mobile1_052009 _______________________________________________ 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.
