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