I have an application where I'm taking 40kHz piezoelectric transducers and installing them in keg lids to report how much beer is left. The environment is admittedly hostile -- the tank is cold (3-10C), pressurized (~10psi), and full of a wet, sugary liquid. I'd expect a certain amount of component failure, after a few years. Instead, I'm seeing a significant number of cases where transducers are failing within a few months.
The transducers in question are the PUI UTR-1440K-TT-R. According to the datasheet, they're rated for 120Vp-p at 40kHz at a very broad temperature range. (Link to Digikey for more info: https://www.digikey.com/product-detail/en/pui-audio-inc/UTR-1440K-TT-R/668-1550-ND/6071962). I'm using a 24VDC power supply, with no transformer, so I wouldn't expect voltage alone to be causing the failures. Aside from the aforementioned hostilities, there's no other engineering challenges -- no extreme heat, no cold below freezing, no vibration or mechanical shock, and so on.
First question: My test for failure is, initially, to look at the signal on the oscilloscope. Returns begin to get weaker, noise begins to increase relative to signal. Eventually, signal goes away entirely. When I pull transducers out of systems that have failed and apply a volt-ohm-meter, I find that there is relatively low resistance across failed transducers. While a known good transducer is typically showing infinite resistance, a failed transducer shows much less, sometimes as little as 2kOhm. Is resistance a good test for failure? Is there a smarter test that I should be using to confirm failure?
Second question: What would cause piezoelectric transducers to fail in this environment? Is there some combination of factors that's causing a problem? Does my test for failure indicate anything about the mode of failure? Is it possible that soldering at initial install is causing premature failure?
Thanks in advance for the help.
Dan
The transducers in question are the PUI UTR-1440K-TT-R. According to the datasheet, they're rated for 120Vp-p at 40kHz at a very broad temperature range. (Link to Digikey for more info: https://www.digikey.com/product-detail/en/pui-audio-inc/UTR-1440K-TT-R/668-1550-ND/6071962). I'm using a 24VDC power supply, with no transformer, so I wouldn't expect voltage alone to be causing the failures. Aside from the aforementioned hostilities, there's no other engineering challenges -- no extreme heat, no cold below freezing, no vibration or mechanical shock, and so on.
First question: My test for failure is, initially, to look at the signal on the oscilloscope. Returns begin to get weaker, noise begins to increase relative to signal. Eventually, signal goes away entirely. When I pull transducers out of systems that have failed and apply a volt-ohm-meter, I find that there is relatively low resistance across failed transducers. While a known good transducer is typically showing infinite resistance, a failed transducer shows much less, sometimes as little as 2kOhm. Is resistance a good test for failure? Is there a smarter test that I should be using to confirm failure?
Second question: What would cause piezoelectric transducers to fail in this environment? Is there some combination of factors that's causing a problem? Does my test for failure indicate anything about the mode of failure? Is it possible that soldering at initial install is causing premature failure?
Thanks in advance for the help.
Dan