Electronics > Metrology

Datron Calibrator 7v to 10v conversion with a transformer

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I seem to remember that Dayton had a calibrator (or DVM) that used an inductive voltage divider for the zener 7v to 10v conversion. It was probably a different voltage ratio. The inductive voltage divider provides a very stable but complex voltage ratio.

Does anyone remember the Datron Model number of this unit. Are any schematics available for this section of the unit?

doktor pyta:
Wow, you read my mind!
Yesterday I did this for testing with LTC1043 as modulator and demodulator.

doktor pyta:
Good idea. I have few H11F1.
I will have to provide some dead time between operation of two switches in the demodulator.
My first observation is that it is extremely easy to saturate the core of my divider and it won't work without say 2200uF capacitor connected in series with the input of the divider. The inductance of the input is about 3H. I used Nanoperm core.
Later I will share some results.

Even with a high permeability core one should use a separate feedback on the actual voltage generated by the transformer. The Datron 1281 uses this to adjust the driving voltage. There are two reasons for this: one is the magnetizing current. The second thing is a not so perfect waveform due to parasitic capacitance. So there will not be a perfect square wave, but some ringing - this is why some dead-time is needed. Beside ringing, there will be a slight slope from the magnetizing current / winding resistance - so the exact timing and demodulator can have an influence.

With high permeability cores one should be careful about applying mechanical stress to the core - this can have an influence on the AL value and thus inductance. It really helps to have a core with very low magnetostriction. I would consider this more important that high permeability by itself. So the simple metgals is not a good choice.

The Datron circuit get's away without an DC isolating capacitor, by using a split coil for driving and having a strictly symmetric waveform (from a divide by 2 circuit).  Having a not so perfect 50% duty cycle and a coupling capacitor to compensate would cause non equal voltages for the two parts.

The H11F1 is good, but I don't think you have to care so much about charge injection, as the transformer usually is not that high in impedance. It would already takes 4 switches to build two demodulators.

I got the Datron 1281 information, thanks!

Is there some parameter that indicates magnetostriction or is it something you have to test for different families of magnetic materials?

I was thinking about applying a symmetrical trapezoid waveform (around 400 hz) to control the bandwidth applied to the transformer. The 72% tap would pass through a buffer before it went to the a synchronous rectifier to demodulate it.

The Direct Current Comparators use many tricks to make the transformers "ideal". I will have to see what can be learned there. So much to learn, it's great!


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