First, you should make sure that the Acquisition License is "Enabled" to recognize the Laser Tach by following these instructions: Do I need to do anything special to use my New Feature (Iris MX™, High Speed Plugin, Iris M™ Tachometer, Iris M Color Camera, Modal Amplified™, and Iris Explorer™ (Spot® Payload)) for the first time?
Then, we have this FAQ explaining the hardware connections: How do I connect the Laser Tach to the Camera to take an "External Sync" recording?
The final tidbits are:
1) Make sure you use LOTS of light
2) Contrary to a "Standard" recording, set the Brightness and Gain as low as possible and as high as possible, respectively. Below is a sample of what I mean. The software will "recommend" settings, but you can customize them to get a clean crisp recording, the lower the Brightness setting the better. You'll be introducing "noise/grain" with the increased Gain, but you can filter it out after the collection. As you record different assets with different running speeds, you'll find that a lower Brightness will give less of a "smeared" image at the higher speeds. It controls the "exposure" time of each frame. Think of it as a shorter snapshot for each sample. I've seen good recordings with the Brightness as low as 0.01 - If the speed is that fast, see #1 above!
3) Filter - Since your Fmax is limited to 1/2 Running Speed (the Tach sets fps equal to running speed - you don't even get a slider, so Fmax will be half that), use the "HDR" filtering mode.
A) Find a peak, again, there will likely be several and they can be an "aliased" frequency since the Fmax is so low.
B) Right-click and select "Initiate Filtered Recording for XXX CPM>HDR"
C) The Filtering window will open and it will be linked to the ROI and Peak selected - notice the 4.11 Hz "Included Frequency" below. Keep the default values as a starting point and click "Apply"
D) Your final product will show you the "non-synchronous" motion. In the attached .GIF, Frankenstein is running, but the coupling between Motor and Gearbox is "frozen" by the Tach. Everything else that's moving in the video is at a frequency that is not the same speed as the coupling.