How Is Phase Measured With A Strobe Light ?

This involves several steps - each one designed to satisfy one of the rules for measuring phase. We must start with a couple of assumptions. We have a machine with a 'problem' - higher than desired amplitude at a particular frequency. The frequency we are concerned with in this case (for simplicity sake) is 1x rpm.

Step #1 - Mount Transducer The first step in collecting a phase reading is to place the transducer on the bearing in the direction desired.  The transducer provides the analyzer with the vibration signal necessary (as per Rule #3). Step #2 - Locate a Reference Mark Commonly a key or keyway, this mark is what we will be using as our 'clock face' reference when it shows up under the strobe flash (as per Rule #4).

Step #3 - Tune the strobe to 1x rpm (the pertinent frequency) Tuning the strobe light properly will freeze the shaft with 1 mark as shown here. Be careful you haven't tuned it to 1/2 rpm since that will also show 1 mark. By tuning the strobe light, you have told the analyzer at which frequency we will be measuring phase (as per Rule #2).  With a strobe light (as opposed to a photoeye). This allows the analyzer to focus on a specific vibration signal - a relatively clean sinusoid (since all other frequencies are being filtered out) that is occurring at or very close to (+/- 0.75%) the tuned frequency. You can compare this to what a radio does - it tunes to one frequency and filters all others out.