Notes from the Test Bench
By Bruce Hofer, Chairman & Co-Founder, Audio Precision
I thought I’d share a real world engineering experience I had over the weekend.
I’ve been tracking down some sources of noise in a new amplifier design I’m working on. To see whether my modifications were actually helping, I needed a repeatable value accurate to the third decimal point, despite the inherent instability that comes with noise. I probably could have used my 2722, but instead I decided to try the new derived measurement feature in APx.
Message to all die-hard S1 and 2700 users: it’s a lot easier with APx.
I started by selecting the APx Measurement Recorder (what we called Time Sweep in S1.exe) and ran the THD+N Level measurement for 60 seconds, which generated a sweep with several hundred points. Then I just added a Mean derived result, to give me a highly repeatable single value result for noise.
With the single value in hand, I can fingerprint individual noise sources, and identify which ones are causing problems as I work on the circuit.
Of course, there are still days when I go to my 2722, either because I need that extra 10 dB of performance, or because I’m working on a really esoteric problem that demands really esoteric sweeps; but with every release of APx500, those situations are getting rarer.
Output: Migration from System One to APx
With the release of the APx515, many production lines that had been keeping their System Ones alive by any means necessary are now making the move to a more modern platform that doesn’t risk shutting down an entire line because a fifteen year old piece of test gear failed.
One of the most common concerns System One users have when looking at migrating to APx is how to translate their old DOS S1.EXE or APWin procedures into something that APx understands. AP’s legacy analyzers have a totally different architecture than the APx. APx’s new measurement-centric paradigm is significantly faster to develop test programs in and is much easier to use, but this ease-of-use means it takes a little bit of work to port test sequences.
While it’s true that there’s no button to press that will convert an S1 procedure into a new APx project, migrating tests is a straightforward process:
In the legacy software, selecting a measurement meant setting one or more of the following: analog or digital generator signal, analog generator output configuration, digital interface configuration, analog or digital analyzer meter, DSP program, regulation panel, and sweep panel.
In APx500, the listed measurements are simply named as such in the measurement navigator.
IMD level sweep in APWin.
For example, setting up SMPTE IMD (Intermodulation Distortion) in the legacy software requires the following steps: select the IMD generator signal, select the IMD analyzer, and then select the IMD data source in the sweep panel. In APx500, on the other hand, you simply add the IMD or IMD Sweep measurement to the Navigator.
IMD meter and level sweep measurements in APx500.
One of the reasons System One was so popular was its high degree of flexibility. However, for many tests that required writing S1 procedures, APx500 has the functionality built directly into the user interface. In the few cases (like loops or if-then logic), where there is no direct equivalent in the APx500 Measurement Navigator, the APx500’s API can be employed to do just about anything.
AP Legacy to APx Migration: Measurement Conversion Chart (download full-size PDF).
A helping hand
For these situations, AP has published a pair of new Technotes which detail migration from DOS S1.EXE and Windows APWin/AP2700/ATS to APx500. The Technotes include a number of charts, including the one shown above, to help make the conversion to APx500 smooth.
Once your tests have been ported to APx500, it will be much easier to manage them moving forward—for example, when you need to edit limits, or want to share sequences with other APx users. You’ll also have access to a whole new world of features, like custom reporting using Word, adding images to your user prompts, and locking your projects to prevent accidents on the production line.
Of course AP’s tech support team is always available to help if you get stuck.
Sound Advice: From the AP Knowledge Base
Level vs. Amplitude in AP2700/APWin/ATS
Q: I want to make a frequency response measurement. Should I use Analyzer.Level A or Analyzer.Amplitude A in the Data 1 section of the Sweep panel? What fundamentally is the difference between the Level and Amplitude meters?
AP2700 Analyzer panel showing the level and amplitude meters.
A: The Level meters have superior response flatness and amplitude accuracy, but are fully specified only down to 5 mV. However, they are useful for most applications at amplitudes far below that. They are always RMS responding, and are located before the bandwidth and filter stages of the input.
The Amplitude meter has five different detector responses (RMS, Average, Peak, Quasi-Peak (Q-Peak), and Sine Scaled Peak (S-Peak)), and can be filtered and bandwidth limited. Bandwidth limiting is very important when out-of-band components of the signal (switching noise, converter noise, high-frequency bias, etc) are significant and may contribute errors to the response measurement.
AP2700 and ATS OLE Automation in Windows 7
When accessing AP2700 or ATS control software via the API, such as from a Visual Basic application, Windows User Account Control (UAC) notifies the operating system before changes are made that require administrator-level permissions. This notification causes an error under API control which terminates the automation process. The issue does not affect AP Basic macros running inside of AP2700 or ATS.
To prevent this error, go to Control Panel > System and Security > Action Center > Security > User Account Control > Change Settings and change the setting to “Never Notify”. A reboot of the system is required for the change to be applied.
Windows User Account Control is designed to notify you when software attempts to make changes to your computer. Changing the setting to “Never Notify” means that if you’re logged on as an administrator, programs can make changes to your computer without you knowing about it. If you're logged on as a standard user, any changes that require the permissions of an administrator will automatically be denied.
Windows User Account Control protects your PC, along with Windows Firewall and other Internet security and anti-virus software. Disabling UAC may open up your computer to potential security risks.
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