[volt-nuts] HP 741B AC-DC Differential Voltmeter/DC Standard
All- Recently picked up an HP 741B, a cousin of the 740B. Wondered if anyone had ever heard of/used/owned this particular model? Strikes me as somewhat of an odd beast in that it shares the same reference oven, production period and ostensibly similar niche as the 740, with the notable addition of AC measurements, yet it has slightly lesser performance (Stability is 3ppm/hr setting, 1ppm/hr range vs 1ppm/hr setting, 0.5ppm/hr range). Curious as to who the target market was? Seems like the 740B would be the choice for DC and another mfr for AC, particularly since it doesn't offer a built in standard. Beautiful cosmetic condition inside and out. No signs of someone messing around with the internals in a past life. Reference oven is good and provides output on the 1V range, but unfortunately the 10, 100, 1kV outputs are nil. Visual inspection didn't offer any overt failures, but given the issue is on all ranges except that which is coming straight out of the ref, the issue likely resides between the diff amp/power switch assy and output. For those in the know, everything probed as expected except the collectors of A7Q1 and A7Q2, which were flat. Anyone have any pearls to share that may save me some time? -Nick ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
[volt-nuts] Oven thermal insulation
I am working on a voltage reference deisgn that will go into an oven for the highest stability. I am looking for a good insulation material that can stand high temperatures safely (up to 80C). Looking at some HP frequency standard ovens I see a hard, light-weight insulation material of some type that looks like it would work really well, but I have no idea what it is. Does anyone have any suggestions? Thanks, Randy Evans AE6YG ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Oven thermal insulation
You might look at AeroGel. Example here. http://www.ebay.com/itm/Aspen-Aerogel-SPACELOFT-Insulation-Hydrophobic-Mat-10-x-14-Sample-10mm-/171203844436?pt=LH_DefaultDomain_0hash=item27dc8b5954 - Original Message - From: Randy Evans randyevans2...@gmail.com To: volt-nuts@febo.com Sent: Monday, July 06, 2015 8:43 PM Subject: [volt-nuts] Oven thermal insulation I am working on a voltage reference deisgn that will go into an oven for the highest stability. I am looking for a good insulation material that can stand high temperatures safely (up to 80C). Looking at some HP frequency standard ovens I see a hard, light-weight insulation material of some type that looks like it would work really well, but I have no idea what it is. Does anyone have any suggestions? Thanks, Randy Evans AE6YG ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
Re: [volt-nuts] Oven thermal insulation
Randy wrote: I am working on a voltage reference deisgn that will go into an oven for the highest stability. I am looking for a good insulation material that can stand high temperatures safely (up to 80C). Looking at some HP frequency standard ovens I see a hard, light-weight insulation material of some type that looks like it would work really well, but I have no idea what it is. Does anyone have any suggestions? I don't know what HP used, but polysulfone is the usual go-to plastic for insulation in that temperature range. It is available in sheets and blocks and is machineable. Do take care not to over-insulate -- the control loop depends on heat flow across the insulator to provide the pull-down to counterbalance the pull-up of the heater. Too much insulation (thermal resistance) and the controller can raise the temperature quickly, but it takes forever to lower it when the controller overshoots (and controllers always overshoot some if they are set up for a normally-damped response). This results in long settling times, instability, or even thermal runaway. You want the pull-up and the pull-down to be roughly symmetrical (rise in internal oven temperature per unit time with heater fully on approximately equal to decline in internal oven temperature per unit time with heater off). Generally, moderate thermal resistance combined with thermal capacitance (thermal mass) produce optimum system dynamics. Best regards, Charles ___ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
