# variations in measured data pts

#### tinz1

Joined Jun 1, 2018
15
Hi!
Ive aqcuired dig. values from a transmitter, with freq. 12Hz for 49sec.
I got asked to compare sampl. times with theoretical variations in measurement points.
What exactly does it mean and how is it best done?

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
You have to be familiar with sampling and digital measurements first. If you do not know what sampling is, than do not even start with the topic.

#### tinz1

Joined Jun 1, 2018
15
Hmm. I sample about 10 digi. values/sec.

#### ArakelTheDragon

Joined Nov 18, 2016
1,350
If you understand this, why can you not compare it? I can give you the lecture of the MIT from which you will understand nothing, since I will not do it for you. It takes reading first and then asking us. Not that we can not explain it with 1 sentence.

#### tinz1

Joined Jun 1, 2018
15
I am suppose to do a statistic calc. to see the std dev.or what? What I ask for is a method to do the comparison.

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#### Raymond Genovese

Joined Mar 5, 2016
1,658
Hi!
Ive aqcuired dig. values from a transmitter, with freq. 12Hz for 49sec.
I got asked to compare sampl. times with theoretical variations in measurement points.
What exactly does it mean and how is it best done?
You have a distribution of sample times. What does that distribution look like? Characterize the distribution you got using all of the usual descriptive statistics for central tendency, Mean, median, range, SD. Graph it out - is it normally distributed?

Find out what the "theoretical variations" are, e.g., does it say something like 49sec +/- 1 sec?

Compare your observed results with the "theoretical results" - are they in line or not?

That is how I interpret the question. Also, you mention only time and not frequency, I would think that you would want to do both but if you only have duration values then that is all you can work with.

#### tinz1

Joined Jun 1, 2018
15
You have a distribution of sample times. What does that distribution look like? Characterize the distribution you got using all of the usual descriptive statistics for central tendency, Mean, median, range, SD. Graph it out - is it normally distributed?

Find out what the "theoretical variations" are, e.g., does it say something like 49sec +/- 1 sec?

Compare your observed results with the "theoretical results" - are they in line or not?

That is how I interpret the question. Also, you mention only time and not frequency, I would think that you would want to do both but if you only have duration values then that is all you can work with.
Thanks alot! I have about 32 samples, where the data is not changing alot (almost static, small changes due to vibrations) and each of the data have a timestamp.

I made a histogram plot of the density of the data together with the normal distribution. But you mean I could do this with the sample times?

#### Raymond Genovese

Joined Mar 5, 2016
1,658
You said you have about 32 samples...of what exactly? What does a line of data for one of your samples look like?

samplenumber timestamp xxx ?

if so, what exactly is xxx

It's confusing because you started out saying "
I've aqcuired dig. values from a transmitter, with freq. 12Hz for 49sec.
I got asked to compare sampl. times with theoretical variations in measurement points."

But, I also see that you are taking 10 samples/sec and that you have ~ 32 samples. If you could provide more details, I think that it would help.

#### tinz1

Joined Jun 1, 2018
15
You said you have about 32 samples...of what exactly? What does a line of data for one of your samples look like?

samplenumber timestamp xxx ?

if so, what exactly is xxx

It's confusing because you started out saying "
I've aqcuired dig. values from a transmitter, with freq. 12Hz for 49sec.
I got asked to compare sampl. times with theoretical variations in measurement points."

But, I also see that you are taking 10 samples/sec and that you have ~ 32 samples. If you could provide more details, I think that it would help.

Sorry, I mixed up my setups.
So: I have a couple (8) of transmitters (measure pressure) connected in serie and that are forming a bus network. I am taking measurements from each of the transmitter and as fast as the transmitters let me. The measurements are taken continuously for about 20 sec and from this I acquire 30 data points from each transmitter. I save the data and the corresponding timestamp (year-month-day hour:minute:sec,msec) for each transmitter.

This is an example of what I store in an excel sheet:
Code:
Time                    s1       s2       s3       s4         s5     s6       s7        s8
2018-08-21 12:56:13,738 18,20511 18,15024 18,12095 18,19822 18,305   18,30021 18,24143 18,34312
2018-08-21 12:56:14,414 18,25105 18,20457 18,12859 18,22646 18,30282 18,24065 18,19152 18,24398
.
.
.
Moderators note : used code tags to preserve spaces

Last edited by a moderator:

#### Raymond Genovese

Joined Mar 5, 2016
1,658
Sorry, I mixed up my setups.
So: I have a couple (8) of transmitters (measure pressure) connected in serie and that are forming a bus network. I am taking measurements from each of the transmitter and as fast as the transmitters let me. The measurements are taken continuously for about 20 sec and from this I acquire 30 data points from each transmitter. I save the data and the corresponding timestamp (year-month-day hour:minute:sec,msec) for each transmitter.

This is an example of what I store in an excel sheet:
Time s1 s2 s3 s4 s5 s6 s7 s8
2018-08-21 12:56:13,738 18,20511 18,15024 18,12095 18,19822 18,305 18,30021 18,24143 18,34312
2018-08-21 12:56:14,414 18,25105 18,20457 18,12859 18,22646 18,30282 18,24065 18,19152 18,24398
.
.
.
It sounds like you have 8 pressures sensors and you sample all 8 at different times. (calling them transmitters is a little confusing).
So, what is the unit of measurement? Something like millibars or ?
"connected in serie and that are forming a bus network" What is the significance of the network? Are the sensor just a few inces from each other or is there some significance to their placement? For example, is sensor 1 situated such that the pressure is slightly less?

#### Raymond Genovese

Joined Mar 5, 2016
1,658
Also, what is 12:56:14,414 - what does the 14,414 mean? I see the 8 sensor readings that follow but I don't know if that is something important (I think it is) like a standard, or is it somehow related to time?

what is 2018-08-21 12:56:14,414 18,25105 18,20457 18,12859 18,22646 18,30282 18,24065 18,19152 18,24398

#### tinz1

Joined Jun 1, 2018
15
It sounds like you have 8 pressures sensors and you sample all 8 at different times. (calling them transmitters is a little confusing).
So, what is the unit of measurement? Something like millibars or ?
"connected in serie and that are forming a bus network" What is the significance of the network? Are the sensor just a few inces from each other or is there some significance to their placement? For example, is sensor 1 situated such that the pressure is slightly less?
Yes, 8 sensors. Unit is in m.H2O.
The end wires of the sensors are located one inches from each other. The sensors are located in a circle of diameter 10 cm, which make their measurements vary a bit.

Also, what is 12:56:14,414 - what does the 14,414 mean? I see the 8 sensor readings that follow but I don't know if that is something important (I think it is) like a standard, or is it somehow related to time?

what is 2018-08-21 12:56:14,414 18,25105 18,20457 18,12859 18,22646 18,30282 18,24065 18,19152 18,24398
2018-08-21 12:56:14,414 is the data & time [yyyy-mm-dd hh:mm:ss,msec] that the measurement was taken.

#### Raymond Genovese

Joined Mar 5, 2016
1,658
ok, good. So, I am assuming that this is homework? Maybe due tomorrow?

You have said "I got asked to compare sampl. times with theoretical variations in measurement points."
Was there something else specific on theoretical variations? Or anything else about the project that could shed some light on what its purpose was?

Without knowing more, I would say that you would want some descriptive statistics (mean, range and SD at the least)...
For each sensor across each time point, e.g., Sensor1 mean=xx SD=XX R=xx-xx
For all sensors by timepoint, e.g., Time1 sum sensors mean, SD, range
You may also want to specifically adresss something like maximum difference between sensors by timepoint, etc...

Without knowing more about the purpose, that would be my approach. But, do make sure that you address the "theoretical variation" because that sounds like somewhere (probably in discussion about the sensors) variation was discussed and you likely want to be able to compare your observed measures with the predicted measures.

#### tinz1

Joined Jun 1, 2018
15
I am calc. flowrate for each timepoint with the sensors and compare this calculated value with a true flowvalue.

#### Raymond Genovese

Joined Mar 5, 2016
1,658
I am calc. flowrate for each timepoint with the sensors and compare this calculated value with a true flowvalue.
ok so then you want to characterize the error in the sensors. One approach is to convert each of the raw measures (calculated flowrate) to a difference from true flowrate, e.g. the error. Then perhaps calculate a root mean square error for each sensor...in addition to the aforementioned descriptive statistics.