NSMS Fundamentals

• Overview
• Externally Mounted Senors
• Various Measurement Capabilities
• Event Time Determination
• Arrival Times to Deflection Conversion
• Deflection to Stress Conversion
• Complete System Characterization
• Flexible Test Scheduling
• Synchronous Realtime Analysis
• Non-Synchronous Realtime Analysis
• High Cycle Fatigue

Event Time Determination

When has the blade arrived?

What defines this discrete event?

What is the measurement resolution?

When has the blade arrived?

The arrival time of the blade is an important question. Imagine you are in very slow motion. Slow enough that you are able to take a picture every 2 nanoseconds (that’s 0.000000002 seconds). You are taking a picture that is a certain size (this is called your spot). As the blade approaches, a part of the blade edge catches the edge of the picture “frame”. This is recorded. Also the strength of the returning signal allows you to know how much of the blade is being seen. Imagine you have 8 pictures from the time the blade tip first enters in to the viewing frame of the spot until the entire blade is under the spot. the blade arrives halfway between when the probe first senses the blade beginning to pass and when the entire blade is over the blade.

Event Definition

What defines this discrete event?

From the amplitudes and times of the 8 pictures taken over the course of a blade encounter, a curve or line is fitted to these points. Then an “event” can be defined as the point of max amplitude change, and the corresponding time along with it. This method provides highly accurate event descriptions and allows AMS the ability to see responses on the sub-1 mil scale.

On the graph, the red dots represent the pictures taken. Each dot has an amplitude and a time. Our system takes these points and fits a curve (dashed line) to these points. This allows us to take the best possible time at our "event", shown in blue.

What is the measurement resolution?

Trying to define our resolution is a loaded question.  In terms of accuracy, our digitzer cards are on the order of .000000002 seconds. Resolution, however, is theoretically much higher because the event times we are recording come from a curve fit  interpolation, and not any specific data point. An important factor is the spot size. AMS optimizes the spot on the blade tip to be small compared to the blade size but large when compared to the surface texture.