Volt-nutting a KE 230

[VintageNut]

Recently, I picked up a KE 230 for USD$200-ish. The unit was advertised AS-IS.

After a multi-day warm-up the unit is being measured with a KE DMM7510. The 230 is set to output 10V.

The measured statistics are

Average: 10.000911
Std Dev:  248.5 uV
Readings: 396,000
NPLC 5

So, the stability is about 25ppm RMS while my 731Bs are typically 0.X ppm stable in the same rack over the same temperature range.

I am wondering what can be done if anything to make the PWM circuit more stable. Suggestions are welcomed. I have never delved into a PWM voltage generator.

[Alex Nikitin]

I am wondering what can be done if anything to make the PWM circuit more stable. Suggestions are welcomed. I have never delved into a PWM voltage generator.

AFAIK, the 230 does not use PWM, but a DAC chip with an internal reference (DAC80). The reference is supposedly a buried Zener but it is possible that what you observe is the reference drift/noise.

Cheers

Alex

P.S. - the DAC80 chip allows for an external reference connection, perhaps LM329 or even LM399 can be used to improve the performance.

[Marcus_S]

Hi,

I think this looks a bit noisy as I found my K230 to be much more stable (see https://www.eevblog.com/forum/testgear/micro-review-keithley-model-230-programmable-voltage-source/msg955141/#msg955141). But for very best stability the K230 likes a well controlled environment, approx +/- 0,2 °C. My K230 lives in a shelf with some free space in the back. But if the HP66332A in the neighbourhood switches on the fan the air in the back of the instruments gets a little warmer and the signal of the K230 changes in the ppm range...

Best regards

Marcus

[VintageNut]

Hi,

I think this looks a bit noisy as I found my K230 to be much more stable (see https://www.eevblog.com/forum/testgear/micro-review-keithley-model-230-programmable-voltage-source/msg955141/#msg955141). But for very best stability the K230 likes a well controlled environment, approx +/- 0,2 °C. My K230 lives in a shelf with some free space in the back. But if the HP66332A in the neighbourhood switches on the fan the air in the back of the instruments gets a little warmer and the signal of the K230 changes in the ppm range...

Best regards

Marcus

I read your thread. Nice job of reviewing the 230.

Your stability graph is just a few minutes. My measurement of stability is much longer. And, no way I can control the temperature in my home/office.

You should try a 24-hour stability measurement.