Small Oven Controler For Voltage Reference

[Andreas]

Has anyone checked performance of the REF voltage of temperature stabilised buried zener inside the LM723?

Hmm,

I cannot find the term "buried zener" in the current data sheet.
I am reading only "temperature compensated zener".

So from where do you have the term "buried zener" for the LM723?

On the other side: the specified ageing of 0.05%/1000 hours (500 ppm or 3.5 mV per 1000 hours)
would correspond to the measured data with drift in the mV range.

Buried zener references are usually specced with 30 ppm/1000 hours or better.

with best regards

Andreas

[IconicPCB]

Andreas,

You are quite right. I had seen a number of "documents" in the past week or so and for some reason the temperature compensated zener became subsurface buried zener in my mind.

[Wolfgang]

Or, you may try with a "differential method". Using your 16bit datalogger as the "zero indicator" only. You would need a voltage source more stable as the 723''s ref. On that "stable" source wire a 10turn 10k Bourns (or something like that), from the wiper to your datalogger input, the datalogger's gnd lead to the 723 ref output. Set zero with the Bourns at the beginning.

In past I was using a REF01 as the voltage source for the Bourns.

This method may eliminate the 7.10V offset problem. Your logger will show the actual difference between the wiper and the 723. In case the REF01 and Bourns will be put in a temperature stable box, and you will cool/heat the 723 ref only, you can easily get its tempco.
Just an idea..

When you got a data logger with good resolution, the logger itself would be a better reference. If you take a RIGOL M300, your 1 year DC spec is about 28ppm over +/-5°C temp range. There are references as good as that, but they are not cheap if you want it calibrated and with a long time spec.

This site has one: http://shop.voltagestandard.com/main.sc but spec is only up to 30ppm, with 1.8ppm/°C tempco and only 6months. For some 10€.
If you look for an LTZ1000A based one, its probably a few 100€ if its worth anything.