ScanImage 2019 : NI 573X Digitizer Module: Over-voltage Protection


The protection circuit on the NI 573X series digitizer modules will switch to an AC Coupled mode when excessive voltage is detected coming in to the ADC.

This is detected on a frame by frame basis.  When an over-voltage is detected, a warning is printed to the Matlab console. The coupling state is not automatically reset.

A User Function called by the event 'overvoltage' can be used to handle this condition. (See User Functions).


Over-voltage occurs when a signal is far above the highest value usable by the digitizer; the input is far above saturation. If you are repeatedly experiencing this problem, you probably need to adjust your laser power or the gain on your PMT/amplifier.

Reoccuring over-voltage can have a negative effect on the FlexRIO digitizer module and should be avoided as much as possible.


Peaks in the signal voltage can be caused by signal reflections in the transmission line between the impedance amplifier and the digitizer. These reflections can occur if the signal source (transimpedance amplifier) and load (digitzier) are not correctly impedance matched. The input impedance of the NI5732/NI5734 FlexRIO adapter modules is 50Ohm. Use matching 50Ohm cables, and ensure that the transimpedance amplifier output impedance is 50Ohm.



ABORT your current acquisition and restart it.  The coupling is automatically reset when you restart a FOCUS, GRAB, or LOOP.

Advanced Solution


Check the current overvoltage status by executing the Matlab command

Reset the coupling mode to DC by executing the Matlab command
hSI.hScan2D.hAcq.channelsCoupling = 'DC';

Both Matlab commands can be executed when ScanImage is idle or during an active acquisition.

In the latest ScanImage releases, use the following command to reset the coupling mode to DC:

DC Overvoltage error message


IMG_0680.JPG (image/jpeg)
DC Overvoltage recovery.png (image/png)