Ultrasound tape measure characteristics and limitations
Question 160S: Short Answer		
Some limitations of an ultrasound tape measure
The graphic below shows an ultrasonic tape measure being used to log the swinging motion of a rather small pendulum bob. Study the graphic and answer the questions that follow.

1.	Identify two problems with these data for the pendulum motion.

2.	Suggest possible causes for the two problems you have identified.

3.	Suggest how you might alter the experimental set up to get a better distance log of the swinging motion of the pendulum.

Quantitative problems on limitations of the tape measure
4.	The closest measurable distance from an ultrasound distance sensor is 0.126 m. Calculate the longest time of duration this allows for each pulse of ultrasound waves emitted. Remember that the device operates on the echo principle.

Take speed of sound = 340 m s-1.
5.	The ultrasound waves in the pulse are at a frequency of 200 kHz. How many wavelengths of ultrasound are there in each pulse?

6.	From the graphic, count the number of pulses that the ultrasound sensor emits in one second.

7.	Use this information to calculate the maximum range of the tape measure transmitting at this rate of pulses.

8.	Suggest how the makers could modify the pulse rate to give a maximum range of 12 m. Suggest why 12 m might be the maximum limit for this sensor.