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EPOCH 4PLUS
Your selections for low and high filter frequencies are generally a function of the
transducer frequency. We recommend that you select a High Pass Filter setting below the
transducer frequency being used and select a Low Pass Filter setting above the transducer
frequency being used. For example, if a 10 MHz transducer is being used, a High Pass
Filter Setting of 8.0 MHz and a Low Pass Filter Setting of 12.0 MHz may provide the best
signal to noise ratio. Due to down shifting of frequency and other material variations, you
may need to adjust the filter selection when actually testing a material in order to
maximize ultrasonic performance.
Note: To select a single filter setting suitable for a wide range of transducer
frequencies, select the ByPass setting for both Low and High Pass Filter
settings. This results in the EPOCH 4PLUS operating in a broadband mode
with a bandwidth of 25 MHz at –3 dB. In this mode, the filter selections do
not have to be adjusted when a different transducer is used. However, the
signal-to-noise performance of the instrument is better if filters are used to
help eliminate noise from outside the test frequency spectrum.
To select the Low and High Pass Filter settings, follow these steps:
1. Press [PULSER] multiple times until the desired filter selection is highlighted, or
press [2ND F], [PULSER] (FILTER) to go directly to the filter selections.
2. Use the function keys for direct access to the preset selection, or use [] and [] keys
to change the selection.
4.4.6 Pulser Type Selection
The EPOCH 4PLUS is equipped with both a negative spike excitation pulser and a tunable
square wave pulser.
To choose the pulser type, follow these steps:
Step1: Press [PULSER] multiple times until the highlight bar is over the pulser selection.
Step2: Use the function keys or use the [ ],[ ],[ ] and [ ] keys to change the selection
to either Spike or Square.
Step3: Use the square wave pulser to provide the best ultrasonic performance for a wide
range of applications, because the pulser can be tuned to best match the transducer
being used (See Pulser Frequency Selection on page 35). The square wave pulser
generally performs best when using low frequency transducers (10 MHz and
below).
Step4: Use the spike pulser to simplify the operation of the EPOCH 4PLUS so that the
pulser frequency does not have to be adjusted (See Pulser Frequency Selection on
page 35). Generally, the spike pulser yields better results when using high
frequency transducers (above 10 MHz). In practice, try both pulser settings and
adjust other parameters during calibration to determine the best settings for the
application.
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