Incorrect Scan Results When Using DMM and Switch in PXI Chassis

Updated Jul 2, 2026

Reported In

Hardware

  • PXI Chassis

Driver

  • NI-DMM

Issue Details

I am using a PXI or PXIe system with a digital multimeter (DMM) and a switch module to perform scan-based measurements.
 
When I run a scan list (for example, path1; path2;), I see the same measurement value for multiple paths instead of different expected values.
 
If I modify the trigger configuration or attempt to use handshaking, I receive timeout errors such as:
 
Max Time exceeded before operation completed. Error code: -1074126845
 
This issue occurs consistently in a PXIe system, even though the same application works correctly in a previous PXI setup.

Solution

This issue can occur when modules are installed in different trigger bus segments in a multi-segment PXI or PXIe chassis.
 
Use one of the following solutions:
  • Configure trigger routing in NI MAX:
    1. Open NI MAX.
    2. Navigate to Devices and Interfaces.
    3. Select the PXI or PXIe chassis.
    4. Open the Triggers tab.
    5. Configure a static route between trigger buses using options such as Away from Bus 1 or Away from Bus 2.
    6. Click Save.
  • Move modules to the same trigger segment:
    1. Check the slot locations of the DMM and the switch module.
    2. Determine whether they are located on different trigger bus segments.
    3. Move one of the modules so both are installed in the same segment.
After applying either solution, run the application again and confirm that measurements update correctly between scan paths.

Additional Information

Some PXI and PXIe chassis use segmented trigger buses. Each segment contains its own set of trigger lines, and these segments are not connected by default. For example, the PXIe-1095 chassis is divided in 3 Bus segments as shown in the following image.
 
Trigger Bus Segmentation for a PXIe-1095 Chassis. Dotted Lines are part of the Timing and Synchronization Upgrade variant for this chassis.
Note: Dotted segment is only available on the Timing and Synchronization Upgraded version of this chassis. 
 
If modules involved in synchronized operations are placed in different segments, trigger-based communication cannot occur between them. This prevents proper synchronization between switching and measurement operations.
 
NI drivers handle trigger routing differently depending on the device type:
  • Devices that use the NI-DAQmx driver can automatically establish trigger connections between modules. This behavior is referred to as dynamic or implicit routing, where the driver configures the required trigger paths at runtime without manual intervention.
  • Devices such as DMMs do not support automatic trigger routing across segments. In these cases, you must configure trigger connections manually using static routes in NI MAX.
Because of this difference, applications that rely on NI-DAQmx devices may work without additional configuration, while applications using DMMs or other instrument drivers may require manual trigger routing or hardware reconfiguration.

Related Links

Other Support Options

Ask the NI Community

Collaborate with other users in our discussion forums



Request Support from an Engineer

A valid service agreement or active software subscription may be required, and support options vary by country.