Uncertainty of an oscilloscope frequency, read from the period

  • #1
2
0
Homework Statement:
Uncertainty for lab reports
Relevant Equations:
T = 1/f
Hi, I am unsure of what uncertainty to get, so here is my full question: I used the CRO for an experiment, and since what I need is frequency, I read the period, so for the uncertainty of the period, it is the smallest division divided by two. So if my uncertainty for period is 0.001s, then what would be the uncertainty of the frequency? Do I need to use error propagation?
 

Answers and Replies

  • #2
hutchphd
Science Advisor
Homework Helper
3,740
2,896
Yes you do, but that is always true. So how do you approach this one?
 
  • #3
2
0
Yes you do, but that is always true. So how do you approach this one?
Is it considered as a polynomial function? since f = 1/T, so f = t^-`1, thus df/dt = -1/t^2, and then do I just substitute t=0.001 into the equation to get the uncertainty?
 
  • #4
haruspex
Science Advisor
Homework Helper
Insights Author
Gold Member
2020 Award
37,143
7,271
thus df/dt = -1/t^2
Right.
do I just substitute t=0.001 into the equation to get the uncertainty?
No.
##\Delta f=\frac{df}{dt}\Delta t##.
The derivative needs to be evaluated using the value of t measured.
 
  • Like
Likes zzzriprip and Delta2
  • #5
hutchphd
Science Advisor
Homework Helper
3,740
2,896
Is it considered as a polynomial function? since f = 1/T, so f = t^-`1, thus df/dt = -1/t^2, and then do I just substitute t=0.001 into the equation to get the uncertainty?
As @haruspex points out the 0.001s is Δt and you need to also put in t. If you do a little algebra on your result above you can show for this case the percent uncertainty in f will be the same as the percent uncertainty in t (i.e. Δt/t). That makes it easy to understand and use.
 
  • Like
Likes zzzriprip and Delta2

Related Threads on Uncertainty of an oscilloscope frequency, read from the period

  • Last Post
Replies
2
Views
790
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
1
Views
639
  • Last Post
Replies
9
Views
5K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
5
Views
5K
  • Last Post
Replies
5
Views
6K
  • Last Post
Replies
1
Views
1K
Top