(S1W3) Electromyography (EMG) part 4

Question 1

What are the 2 types of resolution in EMGs?

Answer 1

• amplitude resolution
• temporal (time) resolution

Question 2

amplitude resolution

Answer 2

• the size of the signal - how many different values can it be
• lower resolution = the digital signal doesn’t reflect the real signal
• increasing resolution = digital signal is more accurate and reflects real signal
• often the peak of the signal is where the error is biggest (the part we are most interested in)

Question 3

ADC amplitude resolution (bits)

Answer 3

• called bits
• number of bits = 2 to the power of that number
• e.g. 8 bit = 2^8 = 256 steps

Question 4

Why is the number of bits important?

Answer 4

• If you are choosing a system, you have to work out is it sensitive enough?
• E.g. an accelerometer in a GPS unit, with a range of -20G to +20G in acceleration, and it’s 8 bit - there are 256 steps between -20G to +20G - is that sensitive enough for what I want?

Question 5

temporal (time) resolution

Answer 5

• also known as sampling frequency
• for sEMG could range from 10-400 Hz
• high temporal resolution = a lot of data
• temporal resolution too low = alias meaning digital signal doesn’t reflect real signal

Question 6

What does EMG measure?

Answer 6

muscle excitation

Question 7

Where should an EMG sensor be positioned?

Answer 7

• belly of the muscle
• parallel to muscle fibres

Question 8

What issue is caused by a sampling frequency that is too low?

Answer 8

alias (digital signal not reflecting real signal)