We need to take into account electromagnetic compatibility (EMC) guidelines for NI PXIe-4138/4139.
This products were tested and complies with the regulatory requirements and limits for EMC stated in the product specifications
. These requirements and limits provide reasonable protection against harmful interference when the product is operated in the intended operational electromagnetic environment.
Referring to GETTING STARTED GUIDE document of NI PXIe-4138/4139, on page 2
the maximum allowable cable length is 3 m (10 ft).