[time-nuts] Poor man's oven

Charles Steinmetz csteinmetz at yandex.com
Tue Jun 6 11:55:23 EDT 2017

Poul-Henning wrote:

>> what I'm interested in is at which exterior temperature
>> OCXO ovens work best ?

Jim replied:

> Here's my guess...
> 1) you want minimal gradients across the device for a variety of reasons
> 2) therefore you want least amount of heat from the heater
> 3) therefore somewhat below the setpoint of the heater.

It depends on what you mean by "best."  "Best" can mean "minimizes the 
wander in oven-regulated temperature at a constant (or slowly-changing) 
ambient temperature," or it can mean "fastest recovery when the ambient 
temperature changes more rapidly."

Minimum heater power tends to favor the first, but be careful -- this 
means a low *available* (maximum) power, not just using a high-powered 
heater at a lower output.  This is because the rate of temperature 
change for full-scale heater swings is proportional to maximum heater 
output, not to the ambient-to-oven differential, and this "granularity" 
of the heater control function is what determines the oven wander at a 
constant (or slowly-changing) ambient temperature.

A higher differential between the set point and ambient, and higher 
maximum heater output, are necessary for fast recovery from larger 
and/or faster changes in ambient temperature (i.e., to achieve a higher 

Note that the above is why, for an oven controller with decent loop 
gain, it is not necessary to control the ambient temperature very 
tightly -- it is only necessary to slow down the *rate of change* in 
ambient temperature to the point that the loop can track it to the 
required tolerance.  See previous list discussions of "cast aluminum 
boxes" and "thermal capacitance."

Best regards,


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