Measured LMA Value Changes with Vertical Range Setting

Updated Apr 9, 2020

Reported In

Hardware

  • Micropross Accessories

Other

HW: MP500 TCL3 or MP500 PT1
SW: MPManager or MPuLib

Issue Details

I am making an load modulation amplitude (LMA) measurement using the MP500 TCL3 and I noticed that the measurement is changing as I change the vertical range setting. The measured LMA value should not depend on the vertical range setting.

Why is this occurring?

Solution

On older versions of MP500 firmware, the LMA detection algorithm does not account for clipping due to over-range conditions. 

The algorithm searches for LMA on clipped voltages which exceed the vertical range of the Analog In port. Eventually it may find something that appears like LMA, but since the voltage is clipped, it detects the peak of the clipped value as the amplitude. Since this peak amplitude is the top of the measurement window (vertical range), as that value doubles, so does the "measured" LMA value. This pattern will continue until the over-range condition is no longer present.
 

To solve this issue, upgrade your MP500 firmware to driver version 1.19 or later. You can find your firmware in your download center under Downloads > MP500.