观察DSO3152A上的波形问题

我正在将我们的一些控制系统（National Instruments cRIO PAC（PLC））转换为使用高速数字输出模块而不是0-10V模拟输出模块。
这主要是为了消除在NI系统外部具有0-10V信号的独立转换器模块的要求，并向我们现有的设备输出脉冲宽度调制波形。
现在我在DSO3152A示波器上看到波形时遇到了问题。
该模块，一个NI 9478 16通道0-50V灌电流数字输出模块（文档），似乎很容易探测，但我无法弄清楚我错过了什么。
我将数字输出（DO）端子探测，参考引线接地到模块上的公共端。
我也尝试过类似于文档第8页的参考线上的Vsup，但无济于事。
有趣的是，我已经能够观察到一个直接响应的波形，并与我用于控制脉冲的程序中的切换相关联，但它是mV级而不是我期望看到的24VDC。
我仍然假设我正在探测这个错误，因为当DO切换到接地时，文档原理图似乎更关注为器件供电，但如果我探测两条线的电位，我不确定这种方法会有什么不同
。
我已经将oscope设置为DC耦合和1X探头以匹配我自己的探头，但我也尝试了其他设置。
谢谢，理查德



     以下为原文

  I am in the process of converting some of our control systems (National Instruments cRIO PAC (PLC)) to use high-speed digital output modules instead of 0-10V analog output modules. This is primarily to eliminate the requirement of having a standalone converter module outside the NI system that is given a 0-10V signal and outputs a pulse-width modulation waveform to our existing equipment. Right now I am having trouble seeing that waveform on my DSO3152A oscilloscope. The module, an NI 9478 16-channel 0-50V sinking digital output module (documentation), seems like it would be fairly straight forward to probe, but I can't figure out what I am missing. I have the digital out (DO) terminal probed with reference lead grounded to common on the module. I have also tried Vsup on the reference lead similar to page 8 on the documentation, but to no avail. Interestingly, I have been able to observe a waveform that directly responds and correlates to my switching in the program I use to control the pulsing, but it is on the mV scale instead of the 24VDC I am expecting to see. I am still under the assumption I am probing this incorrectly as the documentation schematic seems to be more centered around powering a device when DO switches and sinks to ground, though am not sure how this approach would differ if I probed the potential across the two lines. I have set the oscope to DC coupling and 1X probe to match my own probe, though I have attempted other settings as well.  

Thanks,
Richard