Microsecond Timer

Fakopp Microsecond Timer is designed to measure stress wave propagation time in trees. The signal is generated by a hammer tap on the start sensor and the unit displays the measured propagation time. By measuring the distance between the two sensors, velocity can be calculated which can be used to detect hidden decayed parts or holes between the two sensors.

The principle of decay detection is simple. If there is a hole between the two sensors, the generated sound waves can not propagate in a straight line, but they have to go around the hole, therefore it takes longer to reach the stop sensor.

The reference velocity depends on tree species. The following table contains some of the most popular species.

The measured velocity has to be compared to the reference velocity of the species. The relative difference indicates the size of decay between the two sensors. The following table contains the relationship between the relative velocity decrease and the decayed area.

Example calculation

Lets suppose we are testing a scotch pine. The diameter of the trunk is D = 60 cm, this is the distance between the sensors. The measured time is T = 469 microseconds. The velocity is then V = D/T = 60 cm / 469 us = 1279 m/s. The reference velocity of scotch pine is V_ref = 1470 m/s. The relative velocity decrease is (V_ref - V)/V_ref = (1470-1279)/1470 = 13%. This relative velocity decrese signals a decay between the two sensors.
The decayed area ratio is about 10%. So the decayed area is 3.14 x (60cm)^2 x 10% = 1131 cm2. The size (diameter) of decay is 60cm x sqrt(10%) = 60cm x 31% = 19cm.

Package contents

The Fakopp Microsecond Timer package contains:

• Fakopp Microsecond Timer box
• Two SD02 sensors with integrated cables and BNC connectors
• Hammer
• Leather case
• Aluminum reference bar (44 cm long)
• Users Manual
• RS232 cable for PC connectivity
• PC software for raw data aquisition and storage

Technical Parameters