Are Ultrasonic Power Ratings Real?

Nearly anyone who has been involved in the procurement of an ultrasonic cleaning system has come head to head with watts of ultrasonic power issues.  Variations of an order of magnitude or more are common in ultrasonic watts ratings from competitors selling equipment of otherwise similar size and capacity.  Despite the discrepancies, I don’t believe anyone is intentionally trying to mislead potential customers about wattage ratings.  It is true, however, that any competitor is going to do their best to differentiate their product from other competitors in any way they can.  Watts of ultrasonic power provides them an open opportunity to do this.

So why is the variation so huge in ultrasonic cleaning systems?  It boils down to an issue of instant in time vs. average or integrated measurements of power over time.  Assuming that higher numbers are better, let’s consider what contributes to higher “instant in time” numbers – –

• As discussed earlier, the alternating current power line may be the first contributor.  At the peak of the voltage cycle, the instantaneous power in watts is at least double the RMS power delivered to a resistive load.  The discrepancy may be even greater in the case of reactive loads.
• In many cases, ultrasonic generators present a very reactive load.  In simple terms, a lot of things are storing and releasing energy in the ultrasonic generator circuit causing instantaneous power surges as voltages and amperages reach their highest values.
• The ultrasonic transducer varies in impedance with frequency and its acceptance of power varies with impedance.  The variations in impedance during frequency sweep may mean a several fold increase in instantaneous power depending on the frequency sweeping characteristics of the generator output, the “Q” of the transducer and other factors.
• The power output of ultrasonic generators varies widely due to changes in transducer characteristics depending on operating conditions including the work load, liquid depth, chemistry and chemistry concentration, the gas content of the liquid, temperature, etc.  Although there have been many attempts to establish standards for these variables, none has been  successful.  Power readings taken under optimized conditions may be much higher than those in a system in normal operation.

Despite the above, many ultrasonic suppliers are not quick to divulge how they measure and quantify ultrasonic power.  Unless they are a primary manufacturer, they may not even know.  Again, I don’t believe that anyone is maliciously trying to deceive potential customers regarding ultrasonic power but may be collecting and interpreting the numbers differently.

There are measures that an informed consumer can take to help assure “apples to apples” comparisons when evaluating the ultrasonic power capability of competitive ultrasonic equipment –

• Ask how the power ratings are derived and measured.  Specifically ask about peak power and duty cycle compared to the average power over time.
• Ask if the power rating is based on optimized or “normal” operating conditions.
• In some ultrasonic applications, peak power is the key to success.  Ask about peak vs. average power.  Explore the detriment or benefit of peak power in your application and specify intelligently based on the result.
• As a reality check, compare input power to the ultrasonic generator to the claimed ultrasonic power output.  If an ultrasonic generator is rated at 6 amps at 120 volts and has an output rating of 2,000 watts or more, the rating is likely one of peak power.  Energy out can’t continuously exceed energy in.
• Take advantage of the opportunity to submit samples for testing to the supplier’s lab to validate the equipment capability.

In answer to the initial question –  Yes, ultrasonic power ratings are probably “real” but may not be derived and interpreted in the same way.  There is no standard.  This makes valid comparisons based on watts difficult or impossible without additional information.

An upcoming blog will explore the overall viability of generator output watts as a measure of ultrasonic performance capability.

 –  JF  –