How Is Phase Measured With A Photoeye ?
The procedure for collecting phase with a photoeye is somewhat different than with a strobe light. Let's measure phase at 1x rpm as shown here.

Step #1 - Mount Photoeye & Trigger

  • The first step in measuring phase is to properly set up the photoeye. It must be mounted rigidly next to the shaft so it can detect a trigger mark rotating on the shaft. The mark is often a piece of reflective tape. With some modern detectors (like 'Lasertachs'), pattern recognition is used and reflective tape is often not needed. The trigger gives the analyzer a 1x rpm pulse (gives it the frequency).
Step #2 - Mount Transducer
  • Mount the transducer at the location and direction desired.
Step #3 - Instruct Analyzer to collect a phase measurement.
  • A keystroke will tell the box to collect a phase reading.
How does the photoeye calculate the phase angle ?
  • The 1x rpm trigger provides the box with the period of the frequency being measured - the period of 1 cycle at 1x rpm.
  • The box takes that period (measured in seconds) and divides it by 360.
  • Once all the math is completed, the box is ready. When instructed to collect a phase angle, it waits for the trigger mark to pass so it can begin a count up to 360.
  • After beginning it's count, it awaits the arrival of a peak signal from the transducer. The moment it has that, it stops the count. That is the phase angle.
  • For the sake of accuracy, several angles are checked and an average is what is eventually displayed as the phase angle.