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Tutorial: Using Regulation to automate measurements and increase test speed

Created 11 Jul 2008

One of the most useful features of AP2700 and ATS software is regulation. Regulation is a software servo-mechanism that allows the instrument to automatically vary one measurement parameter to achieve a specific measurement result; for example finding the generator level where the output of a device under test has exactly 1% distortion.

Regulation has many possible applications, but in this example we will use it to automatically find the maximum output level of an amplifier and the output level with the lowest distortion, and then automatically control the same amplifier so that its output level is exactly 1 Watt.

For these examples we assume you are already familiar with how to connect your device under test to the instrument and how to configure the analog signal generator and the analog analyzer panel in AP2700 or ATS software.

In this example we will be working with a conventional power amplifier and a SYS-2722 audio analyzer with AP2700 v3.30 control software. This example can also be used with the ATS-2 instrument, and the basic parameters we are going to regulate apply to most audio devices.

To get started, the regulation function can be accessed via its toolbar shortcut, , or from the menu bar via the Panels -> Regulation selection. The regulation panel has the following options:

Target - This is the measurement parameter you want regulated. In our first example we want to find the point at which the output level of the amplifier is at 1% distortion. So the target is Anlr.THD+N Ratio, this will use the value produced by the analog analyzer, THD+N ratio function meter. Value - This is the specific result we want to achieve, in this case we are trying to achieve a THD+N result of 1%, a common value for the definition of amplifier maximum output level. Tolerance - This defines how tightly the target value has to be before the regulation algorithm is satisfied. This can be expressed as a percent of the target value, a dB ratio, or an absolute tolerance. Source - This is the parameter to be varied. In this case the system is going to vary the level of the signal generator.

• High Bound, Low Bound - These parameters control the range in which the source parameter is to be varied. In this case, the system will search for the 1% THD+N point by varying the generator level between 100 mVrms and 2 Vrms. It is important to set the high bound at a level lower than that which will damage the device under test.
• Operation - There are different algorithms available to the regulation function depending on what you are searching for. The +Normal mode is optimized specifically for the non-linear characteristics of amplifiers near their clipping points. We will also use the minimum mode which searches for the lowest target value and the Linear mode which searches for a specific target value in devices operating in a linear fashion.
• Stepsize - Controls how large the steps are as the system searches for the Target parameter. The system automatically lowers the step size as it gets closer to the target parameter, so this can usually be left at the default setting, but if the range (high bound to low bound) is large, increasing the step size will speed up how long it takes the instrument to find the desired parameter.
• Iterations - This is the total number of times the instrument will try to vary the Source parameter to find the Target measurement. Again, usually the default value will work well, but if the high bound to low bound range is large or the Tolerance value is small, you may need to increase the number of iterations.
• Timeout - This is the amount of time the system should spend at each step to try and get a stable measurement. This parameter almost never needs to be changed from the default.

In our first example, we set the target parameter to be the analog analyzer THD+N ratio function meter. We have entered a value of 1% distortion. We are going to find this value by varying the analog signal generator between 100 mVrms and 2 Vrms. Since we are looking for a non-linear property, we are going to use the +Normal operating mode.

With the amplifier used in this example, after clicking on the Regulate button, the system found that with a generator level of 477 mVrms, the output of the device with 1% THD+N is 18.3 Vrms or 41.88 Watts in to an 8 Ohm resistive load. If we try this again, but set the target value to 10% distortion, the system finds that a generator level of 590 mVrms achieves 50 Watts of output from the amplifier.

In the next example we will use regulation to find the point at which the amplifier exhibits the lowest THD+N ratio, the output level at which the device has the best distortion performance. In this case we are once again looking at THD+N Ratio as the target parameter, and we will be varying the generator amplitude, but the operation mode is now Minimum and we have changed the high and low bound to be closer to range where the best distortion point is to be found. After regulation the instrument found that with a generator level of 95 mVrms, the output of the amplifier was 1.7 Watts at 0.004% THD+N. Finally, many technical standards such as CEA-490A call for devices to be tested at specific output levels. We can use regulation to quickly and easily find those levels. In this example we will use the Linear mode of operation to vary the generator level until the output of the amplifier is exactly 1 Watt. In this case we change the target to be the analog analyzer level meter and we set the target value to 1 W. The varied parameter will still be the generator amplitude, but we will use the Linear operation mode. After clicking on the regulate button the system finds that 73.4 mVrms results in precisely 1 Watt of output from the amplifier. Regulation is a powerful tool for automatically finding measured values related to a varied parameter. For more information please consult the AP2700 or ATS-2 software user manuals or online help. Also, Audio Precision has the world's best technical support department. Feel free to contact them at techsupport@ap.com or 800-231-7350 (USA toll free) and 503-627-0832.

Regulation panel with Minimum mode selected. Regulation panel with Linear mode selected.

 

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