Re: [volt-nuts] Oven thermal insulation
Chuck wrote: Bear in mind that the common ordinary styrofoam cup does just fine when containing boiling water. Sure, for the 4-5 minutes the water stays above 70C. But over 5-10 years 24/7/365 I once broke my office coffee cup and temporarily used a styrofoam cup as a replacement. I brewed tea in it once or twice a day, and in just a few weeks it had gone through significant dimensional changes (it was a little smaller and somewhat irregularly shaped). 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.
[volt-nuts] Oven thermal insulation
Hi Randy, 80°C and 'highest stability' is simply a contradiction in itself. Therefore, if you really go for highest stability, please run your voltage reference at 60°C only, best would be 45°C! In this case, ordinary styrofoam is suitable, higher temperatures require poly sulfone, like used on the HP3458A reference board, or the VALOX(TM) plastic which is used for the LM399. Frank ___ 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
Not after looking at the price you won't! Prices around USD300 for an 8' by 4' sheet for 50mm thick. Regards, David Partridge -Original Message- From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Tom Miller Sent: 07 July 2015 03:07 To: Discussion of precise voltage measurement Subject: 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 ___ 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
Frank, I don't plan on operating at 80C. I just want an insulation that can withstand up to 80C so i have a safety margin. 45C is probably too low for my environment but 50C might be doable. Thanks, Randy On Tue, Jul 7, 2015 at 12:29 AM, Frank Stellmach frank.stellm...@freenet.de wrote: Hi Randy, 80°C and 'highest stability' is simply a contradiction in itself. Therefore, if you really go for highest stability, please run your voltage reference at 60°C only, best would be 45°C! In this case, ordinary styrofoam is suitable, higher temperatures require poly sulfone, like used on the HP3458A reference board, or the VALOX(TM) plastic which is used for the LM399. Frank ___ 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, hi again, My idea sounds crude but it worked very well. The outer box was made out of small squares of aluminum drilled and taped with small aluminum angle pieces. I have two references in this oven, a fluke circuit based on the 731b, and one of Doug’s 10 volt references. I run the oven at 45°C. The gray board for the inner cover is ‘GATOR Board’ used to mount prints, it has a foam core. You should also have a guarded transformer, got mine from scrape fluke 510, Dallas On 7/6/2015 10:09 PM, Dallas Smith wrote: Hi Randy, I used a box in a box then shot yellow window or gap fill insulation from your hardware store, use minimal expanding type. Fill around the spaces between the boxes with the tube but very slowly. You will get this on your hands so use your gloves because you will have to hold the boxes in place as it expands. After it dries cut the top off with a bread knife. May take a couple of tries to get what you want. Dallas Date: Mon, 6 Jul 2015 17:43:45 -0700 From: randyevans2...@gmail.com To: volt-nuts@febo.com 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.
Re: [volt-nuts] Oven thermal insulation
I bought a couple of the sample sheets of Spaceloft Areogel (Ebay # 171328843398) a couple monthas ago. Cheap enough at $7.99 for a 10x14 piece with free shipping. It's 5mm thick, and easily cut with scissors. The datasheet that was supplied with the samples say that its max temperature is 200°C, so will surely work in a 45°C oven. R-Value is advertised to be 10.3 per inch. I bought it in anticipation of building an oven for a voltage reference, as you are. I'm still considering the size shape of the box for the oven. Other irons in the fire presently, so not on my front burner. It certainly is a better insulator than fiberglass or Great Stuff foam. I find it rather suspicious that the R-value of Great Stuff doesn't appear in any of the ads, brochures or data sheets. I think its value is more in favor of its use as a sealant trather than as insulation. Cheers, Dave M Randy Evans wrote: Frank, I don't plan on operating at 80C. I just want an insulation that can withstand up to 80C so i have a safety margin. 45C is probably too low for my environment but 50C might be doable. Thanks, Randy On Tue, Jul 7, 2015 at 12:29 AM, Frank Stellmach frank.stellm...@freenet.de wrote: Hi Randy, 80°C and 'highest stability' is simply a contradiction in itself. Therefore, if you really go for highest stability, please run your voltage reference at 60°C only, best would be 45°C! In this case, ordinary styrofoam is suitable, higher temperatures require poly sulfone, like used on the HP3458A reference board, or the VALOX(TM) plastic which is used for the LM399. Frank ___ 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
Bear in mind that the common ordinary styrofoam cup does just fine when containing boiling water. Where it has problems is when it is in contact with the heating elements, and they are allowed to overshoot the desired temperature greatly. The answer is to make sure that your heating element is in good thermal contact with the metal oven, and not in contact with your insulation... That, and don't get too aggressive with the delta t component of your PID algorithm. -Chuck Harris Randy Evans wrote: Frank, I don't plan on operating at 80C. I just want an insulation that can withstand up to 80C so i have a safety margin. 45C is probably too low for my environment but 50C might be doable. Thanks, Randy On Tue, Jul 7, 2015 at 12:29 AM, Frank Stellmach frank.stellm...@freenet.de wrote: Hi Randy, 80°C and 'highest stability' is simply a contradiction in itself. Therefore, if you really go for highest stability, please run your voltage reference at 60°C only, best would be 45°C! In this case, ordinary styrofoam is suitable, higher temperatures require poly sulfone, like used on the HP3458A reference board, or the VALOX(TM) plastic which is used for the LM399. Frank ___ 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.
