Frequency Measurement with NI-9361 not stable

Hello,

I am playing around with a cDAQ-9185 system with a NI-9361 to measure a 60kHz frequency signal.

But the read data abnormal occur periodic. I have tried to changed every parameters even the channel but not work.

As the attached picture show, the normal situation keep 13 sec and the  abnormal keep 18 sec.The waveforms changed periodically.

I have used the Gantner Instruments measured the signal with same sampling rate, the waveform were stable.

Can anybody tell me how to measure frequency with NI-9361 ?

Thanks!