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60 kHz Quartz Tuning Fork Resonator Data

The first batch of 25 resonators:

60 kHz TF26 resonators - Batch 1 data

60 kHz TF26 resonators – Batch 1 data

The second batch from the same eBay source arrived a few months later and I finally got around to measuring them:

60 kHz TF26 resonators - Batch 2 data

60 kHz TF26 resonators – Batch 2 data

A dot of green Sharpie on the AT26 cans identifies the second batch:

60 kHz TF26 resonators - Batch 2 marking

60 kHz TF26 resonators – Batch 2 marking

The alert reader will notice an un-measured 25th resonator at the bottom of the first batch. I dropped one from the second batch under the Electronics Workbench, found it, then also found its long-missing brother; now I have a genuine it’s-never-been-used resonator, just in case the need arises.

A quick-and-dirty simulation shows the series and parallel resonant peaks come out close, but not dead on, the actual measurements:

Simulation - 60 kHz resonator

Simulation – 60 kHz resonator

The model obviously doesn’t exactly match reality, which isn’t too surprising. However, I don’t understand something about tuning fork resonators, because the parallel resonance shouldn’t shift upward with the series resonant peak when the circuit gains a 24 pF series capacitance:

Resonator 0 Spectrum

Resonator 0 Spectrum

Suffice it to say that doesn’t happen with the simulation.

More study is needed, as the saying goes.

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  1. #1 by madbodger on 2017-09-07 - 09:35

    I’m curious about that shifting parallel resonance too. I suspect your implication is correct, and it’s (somehow) an effect of the tuning fork structure (versus the usual twist/shear crystals). It would be tempting to measure a conventional crystal of a similar frequency and see if the same effect appears. At first I figured such things would be unwieldy and nonexistent, but I remembered I have a 100kHz crystal, a pretty little thing with gold contacts housed in a glass housing the same as a 9-pin miniature vacuum tube, and probably a couple in oversized HC-6 packages. So, do I duplicate your device, or send you a couple for testing?

    • #2 by Ed on 2017-09-07 - 11:51

      So, do I duplicate your device, or send you a couple for testing?

      This is America: we can do both!

      The least horrible alternative seems to be sending a couple here. Pack ’em well, I’ll take good care of ’em, and return ’em promptly. Thanks!

      Near parallel resonance, the resonator is mostly inductive and one could model it as a single RL (without internal capacitors). Then the RL would resonate with CX in series mode, which might just account for what I see.

      On the other paw, I can’t find any resonator measurements at 0.1 Hz frequency resolution, so the simple circuit model probably doesn’t capture the physical reality under these absurd conditions. I vaguely recall a more complex model festooned with inductors & capacitors, but …

  1. LF Crystal Tester: 60 kHz Resonator Frequency Distribution | The Smell of Molten Projects in the Morning
  2. 60 kHz Tuning Fork Resonator: Maximum Overdrive | The Smell of Molten Projects in the Morning

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