Originally Posted by Alex Simmons .
I use Campag Profit pedals and am not changing any time soon.
Neither pedal unit permits user to validate calibration, aside from running in unison with another calibrated power meter.
It may not be necessary for the user to calibrate these given that at least one set uses piezoelectric strain gauges. Piezoelectrics have a really high modulus of elasticity compared to aluminum foil strain gauges, meaning that for a given stress, the strain (whether elongation or compression) is very small. It's also known that piezoelectrics have exceedingly long fatigue lives, so long that it's not clear how long that life is. It will be dependent of course on the particular make-up of a given piezoelectric component, which is proprietary in more than a few cases.
I have done calibration work on a piezoelectric optical linear encoder (a device that measures displacement) that had a resolution of 12 picometers (roughly 1/10 the diameter of a Hydrogen atom), but the calibration was necessary as part of the scientific process of validating a new measurement technique. The user can certainly calibrate measurements with the pedal based systems. Any measurement system can be calibrated. Maybe the companies don't provide a step-by-step process for doing it, but it won't take much creativity to come up with one. In fact, right off the bat I can think of several ways of doing that.
Given the stability of piezoelectrics, it's reasonable to assume that any drift in measurement be small. That is the nature of piezoelectrics and one of the big reasons why they're becoming so popular in not only industry for precise and accurate measurement applications, but also in science. With that said, given their new emergence in cycling and healthy skepticism ( a good thing), it's not surprising at all for people to wonder about the calibration aspect, as well as other aspects. Using other power measurement systems is certainly one way to calibrate, and someone or maybe more than someone will offer that service.
Since companies, some at least, are sensitive to such questions and doubts, I wouldn't be surprised to see the companies respond with calibration procedures.
I'm not ready to reject pedal based systems out of hand because no one, except for the companies, has any extensive measurement data. The cycling community has a long history with SRM, PT, and now even Quarq (and I guess Ergomo, and soon Power2Max) so the community's inertia is certainly in favor of those products (the first three, anyway). Hopefully, the well versed people in the industry, such as yourself, will put the pedal based systems to the test by differential measurement with SRMs, PTs, and Quarqs. Certainly without more power measurement product variations on the market, companies like SRM and Quarq will see zero reason to bring their prices down. Look/Polar and Garmin can be forgiven a bit for introducing at higher prices since the market is already a niche market, and they have to be sure to cover their investments. Let's hope both systems work well and that more people buy power measurement systems. That is what will bring prices down, and I think we all want that.