Power Electronics - Sample Rate & Precision
When choosing your next Oscilloscope, you may find the marketplace is littered with banner specifications which are all aimed at catching the eye. After all, every manufacturer wants you to pick their solution over anyone else.
In Power Electronics, the need for precision measurement often sits high on the priority list, sometimes though it is assumed that a high sample rate means that you can capture more sample points which then provides a precise representation of the signal. This would seem logical given that fewer sample points may cause a scope to aliase as shown below:
However, for Precision, the number of sample points is somewhat irrelevant if the accuracy of the measured points is not sufficient.
If you take a typical Oscilloscope and look at the overall accuracy, it could be perceived that those accuracies also apply to all other measurements including power measurement, yet what is sometimes overlooked is the accuracy of the probes used. A typical Current probe can sit at +/-2%, likewise a Voltage Differential probe typically also sits at +/-2%, therefore unless precision is defined as "Scope Accuracy + Probe(s) Accuracy" then how can a test engineer accept the measurement as one that can indeed be deemed as Precise?
"Why Precision? Is +/- 2%, 3%, 10% not good enough?"
"Precision is all around us, in everything we see, everything we touch. It means the difference between success and failure, safe and unsafe, sustainable and unsustainable"
Precision also plays a part on the confidence that the consumer has in your product which in turn carries the reputation of the manufacturing company.
Let's turn the tables for a moment and place you in the position of your customer, if you purchased a product which failed after a short period of time, you may feel obliged to complain, look at a competitor and/or review the products failure in the public arena.
With a 2% (or more) uncertainty, I ask is there sufficient confidence that the product will perform as expected? and better than your competitors product?
Highlighting the issue is only half the job done, overcoming this is the challenge. Many times I have faced this question of overcoming measurement uncertainty and in Power Electronics I come back to the same solution. A product which overcomes the 'Probe measurement uncertainty', a product which, time and time again, exceeds the expectations of test engineers looking to get the best and most precise measurement while still capturing the high sample rate which a scope can offer, yet maintains the same measurement uncertainty as a steady state power analyser.
The solution is the PX8000 Precision Power Scope, a transient Power Analyser capable of sampling at 100MS/s with a measurement uncertainty of 0.1% of Reading + 0.1% of RMS Range.
Below is an image of the modules input connections which are direct connection of up to 1000VRMS and 5ARMS with the option for precision current sensors with a measurement uncertainty of 0.01% which means you can maintain the overall accuracy of the PX8000.
The operation is just like an Oscilloscope too with triggering capabilities, multiple channels, dual zooming yet with a high record length of 100M Points per voltage and current channel.
Specified in AC and DC, the PX8000 has warranted specifications including Active Power which accounts for the phase calculation simultaneous to the Voltage and Current.
Whereas the phrase "A picture speaks a thousands words" could be applicable, I believe a video (non-Yokogawa) showing the differences between a Scope and the PX8000 speaks many more words:
Specifying a product and proving its capability sometimes delivers varying results - see my other article "It Does Exactly What It Says On The Tin"
Proven Precision starts at ￡13,300 and returns confidence, assurance and proof that your measurement is indeed Precise.
Find out more about 'The Precision Makers' and what we have to offer at the Yokogawa Test & Measurement Website
The postings on this site are my own and don’t necessarily represent Yokogawa’s position, strategies or opinions.