[Shimmer-users] Why non-zero acceleration and magnetometer even while no motion

[Weiguang guan]

Hi Shimmer users,

I'm a new user, and run into a weird problem --- I got non-zero
acceleration and magnetometer values from Shimmer sensors even when they
are totally static. Below are two plots (x, y, z components are in red,
green and blue respectively) made from a very simple experiment where
only a linear motion without rotation and there are static periods at
both the beginning and the end. Have you run into problem before? Please
drop a line if you know what happens. Thanks.

Best,
Weiguang

[Jong Chern]

Hi Weiguang,

I would recommend taking a look first at the IMU User Guide,
http://www.shimmersensing.com/images/uploads/docs/IMU_User_Guide_rev1.3.pdf
and then followed by the Shimmer 9DOF Calibration User Manual,
http://www.shimmersensing.com/images/uploads/docs/Shimmer_9DOF_Calibration_User_Manual_rev2.5a.pdf

I hope that helps.

Best regards,
Jong Chern

On 20/01/2015 04:16, Weiguang guan wrote:
> Hi Shimmer users,
>
> I'm a new user, and run into a weird problem --- I got non-zero
> acceleration and magnetometer values from Shimmer sensors even when
> they are totally static. Below are two plots (x, y, z components are
> in red, green and blue respectively) made from a very simple
> experiment where only a linear motion without rotation and there are
> static periods at both the beginning and the end. Have you run into
> problem before? Please drop a line if you know what happens. Thanks.
>
> Best,
> Weiguang
>
>
>
>
> _______________________________________________
> Shimmer-users mailing list
> Shimmer-***@eecs.harvard.edu
> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>
>
> No virus found in this message.
> Checked by AVG - www.avg.com <http://www.avg.com>
> Version: 2013.0.3495 / Virus Database: 4257/8958 - Release Date: 01/19/15
>

[Dale Roberts]

Hi Weiguang,

The Earth's gravity field will always cause a 9.8m/s^2 acceleration on
an object at rest, and, depending on the angle of the Shimmer with
vertical, this will be distributed amongst the 3 accelerometer axes.
From your plot, it looks like initially the Shimmer was sitting at an
angle to vertical, then maybe it was "picked up" or otherwise had its
orientation changed so that it was pretty close to "flat" (i.e.,the Z
axis showed most of the gravitational acceleration), then there was a
sinusoidal movement along the X axis. This is to be expected, unless the
Shimmer is in free fall (or in Earth orbit on the Space Station!), in
which case you would get near zero on all axes.

If you set the Shimmer flat on a table, and you get readings
significantly higher than zero on more than one axis, then maybe indeed
there is something wrong in the data, but I would suspect some data
handling error before I suspected a fault in the Shimmer itself. Do the
accelerometer plots look just like this in ShimmerConnect?

Likewise for the magnetometer, which will always show the Earth's
magnetic field pointing in some direction, unless you put the Shimmer in
a thick iron case.

Hope this is helpful,
dale



On 1/19/2015 3:16 PM, Weiguang guan wrote:
> Hi Shimmer users,
>
> I'm a new user, and run into a weird problem --- I got non-zero
> acceleration and magnetometer values from Shimmer sensors even when
> they are totally static. Below are two plots (x, y, z components are
> in red, green and blue respectively) made from a very simple
> experiment where only a linear motion without rotation and there are
> static periods at both the beginning and the end. Have you run into
> problem before? Please drop a line if you know what happens. Thanks.
>
> Best,
> Weiguang
>
>
>
>
> _______________________________________________
> Shimmer-users mailing list
> Shimmer-***@eecs.harvard.edu
> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users

[Weiguang guan]

Hi Dale,

Thank you very very much for the explanation of the phenomenon that
puzzled me. However, I have different thought about while taking gravity
in to consideration --- if you place a Shimmer sensor on a table, it
will receives both a gravity and a force from the table that supports
it. These two forces cancel each other out, so the sensor stays still on
the table. The accelerations caused by gravity and the upward supporting
force should cancel each other out as well as they are equal in
magnitude and in exactly the opposite direction. As a result, the
Shimmer sensor should have zero acceleration reading, right? When it is
in a free fall, it should have a non-zero reading caused by gravity
only, am I right?

Best,
Weiguang


On 20/01/2015 8:47 AM, Dale Roberts wrote:
> Hi Weiguang,
>
> The Earth's gravity field will always cause a 9.8m/s^2 acceleration on
> an object at rest, and, depending on the angle of the Shimmer with
> vertical, this will be distributed amongst the 3 accelerometer axes.
> From your plot, it looks like initially the Shimmer was sitting at an
> angle to vertical, then maybe it was "picked up" or otherwise had its
> orientation changed so that it was pretty close to "flat" (i.e.,the Z
> axis showed most of the gravitational acceleration), then there was a
> sinusoidal movement along the X axis. This is to be expected, unless
> the Shimmer is in free fall (or in Earth orbit on the Space Station!),
> in which case you would get near zero on all axes.
>
> If you set the Shimmer flat on a table, and you get readings
> significantly higher than zero on more than one axis, then maybe
> indeed there is something wrong in the data, but I would suspect some
> data handling error before I suspected a fault in the Shimmer itself.
> Do the accelerometer plots look just like this in ShimmerConnect?
>
> Likewise for the magnetometer, which will always show the Earth's
> magnetic field pointing in some direction, unless you put the Shimmer
> in a thick iron case.
>
> Hope this is helpful,
> dale
>
>
>
> On 1/19/2015 3:16 PM, Weiguang guan wrote:
>> Hi Shimmer users,
>>
>> I'm a new user, and run into a weird problem --- I got non-zero
>> acceleration and magnetometer values from Shimmer sensors even when
>> they are totally static. Below are two plots (x, y, z components are
>> in red, green and blue respectively) made from a very simple
>> experiment where only a linear motion without rotation and there are
>> static periods at both the beginning and the end. Have you run into
>> problem before? Please drop a line if you know what happens. Thanks.
>>
>> Best,
>> Weiguang
>>
>>
>>
>>
>> _______________________________________________
>> Shimmer-users mailing list
>> Shimmer-***@eecs.harvard.edu
>> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>

[Torstein Adolf Winterseth]

I believe the confusion lies in the difference between "coordinate" and "proper" acceleration.


An accelerometer does not measure "coordinate" acceleration, which is the change in speed. You are correct that the force of gravity is countered by the force the table provides which makes the sum of forces 0 and the Shimmer doesn't move.


However, what an accelerometer measures is the "g-force" of the object. When you are in a plane, you experience gravity which pushes you into the seat (~1 g), but if the plane went into freefall you would float (0 g). That's what the accelerometer measures. That's what he meant that the accelerometer would measure 0 m/s^2 in freefall or in orbit and 9,8 m/s^2 on your table.


Hope this clears it up. :)

Torstein


________________________________
From: shimmer-users-***@eecs.harvard.edu <shimmer-users-***@eecs.harvard.edu> on behalf of Weiguang guan <***@rhpcs.mcmaster.ca>
Sent: 20 January 2015 16:19
To: Dale Roberts
Cc: shimmer-***@eecs.harvard.edu
Subject: Re: [Shimmer-users] Why non-zero acceleration and magnetometer even while no motion

Hi Dale,

Thank you very very much for the explanation of the phenomenon that puzzled me. However, I have different thought about while taking gravity in to consideration --- if you place a Shimmer sensor on a table, it will receives both a gravity and a force from the table that supports it. These two forces cancel each other out, so the sensor stays still on the table. The accelerations caused by gravity and the upward supporting force should cancel each other out as well as they are equal in magnitude and in exactly the opposite direction. As a result, the Shimmer sensor should have zero acceleration reading, right? When it is in a free fall, it should have a non-zero reading caused by gravity only, am I right?

Best,
Weiguang


On 20/01/2015 8:47 AM, Dale Roberts wrote:
Hi Weiguang,

The Earth's gravity field will always cause a 9.8m/s^2 acceleration on an object at rest, and, depending on the angle of the Shimmer with vertical, this will be distributed amongst the 3 accelerometer axes. From your plot, it looks like initially the Shimmer was sitting at an angle to vertical, then maybe it was "picked up" or otherwise had its orientation changed so that it was pretty close to "flat" (i.e.,the Z axis showed most of the gravitational acceleration), then there was a sinusoidal movement along the X axis. This is to be expected, unless the Shimmer is in free fall (or in Earth orbit on the Space Station!), in which case you would get near zero on all axes.

If you set the Shimmer flat on a table, and you get readings significantly higher than zero on more than one axis, then maybe indeed there is something wrong in the data, but I would suspect some data handling error before I suspected a fault in the Shimmer itself. Do the accelerometer plots look just like this in ShimmerConnect?

Likewise for the magnetometer, which will always show the Earth's magnetic field pointing in some direction, unless you put the Shimmer in a thick iron case.

Hope this is helpful,
dale



On 1/19/2015 3:16 PM, Weiguang guan wrote:
Hi Shimmer users,

I'm a new user, and run into a weird problem --- I got non-zero acceleration and magnetometer values from Shimmer sensors even when they are totally static. Below are two plots (x, y, z components are in red, green and blue respectively) made from a very simple experiment where only a linear motion without rotation and there are static periods at both the beginning and the end. Have you run into problem before? Please drop a line if you know what happens. Thanks.

Best,
Weiguang

[cid:***@rhpcs.mcmaster.ca]

[Weiguang guan]

Torstein and Dale,

Thanks a lot to both of you. Now I understand it. Have a great day!

Best,
Weiguang

On 20/01/2015 11:05 AM, Torstein Adolf Winterseth wrote:
>
> I believe the confusion lies in the difference between "coordinate"
> and "proper" acceleration.
>
>
> An accelerometer does not measure "coordinate" acceleration, which is
> the change in speed. You are correct that the force of gravity is
> countered by the force the table provides which makes the sum of
> forces 0 and the Shimmer doesn't move.
>
>
> However, what an accelerometer measures is the "g-force" of the
> object. When you are in a plane, you experience gravity which pushes
> you into the seat (~1 g), but if the plane went into freefall you
> would float (0 g). That's what the accelerometer measures. That's what
> he meant that the accelerometer would measure 0 m/s^2 in freefall or
> in orbit and 9,8 m/s^2 on your table.
>
>
> Hope this clears it up. :)
>
> Torstein
>
>
> ------------------------------------------------------------------------
> *From:* shimmer-users-***@eecs.harvard.edu
> <shimmer-users-***@eecs.harvard.edu> on behalf of Weiguang guan
> <***@rhpcs.mcmaster.ca>
> *Sent:* 20 January 2015 16:19
> *To:* Dale Roberts
> *Cc:* shimmer-***@eecs.harvard.edu
> *Subject:* Re: [Shimmer-users] Why non-zero acceleration and
> magnetometer even while no motion
> Hi Dale,
>
> Thank you very very much for the explanation of the phenomenon that
> puzzled me. However, I have different thought about while taking
> gravity in to consideration --- if you place a Shimmer sensor on a
> table, it will receives both a gravity and a force from the table that
> supports it. These two forces cancel each other out, so the sensor
> stays still on the table. The accelerations caused by gravity and the
> upward supporting force should cancel each other out as well as they
> are equal in magnitude and in exactly the opposite direction. As a
> result, the Shimmer sensor should have zero acceleration reading,
> right? When it is in a free fall, it should have a non-zero reading
> caused by gravity only, am I right?
>
> Best,
> Weiguang
>
>
> On 20/01/2015 8:47 AM, Dale Roberts wrote:
>> Hi Weiguang,
>>
>> The Earth's gravity field will always cause a 9.8m/s^2 acceleration
>> on an object at rest, and, depending on the angle of the Shimmer with
>> vertical, this will be distributed amongst the 3 accelerometer axes.
>> From your plot, it looks like initially the Shimmer was sitting at an
>> angle to vertical, then maybe it was "picked up" or otherwise had its
>> orientation changed so that it was pretty close to "flat" (i.e.,the Z
>> axis showed most of the gravitational acceleration), then there was a
>> sinusoidal movement along the X axis. This is to be expected, unless
>> the Shimmer is in free fall (or in Earth orbit on the Space
>> Station!), in which case you would get near zero on all axes.
>>
>> If you set the Shimmer flat on a table, and you get readings
>> significantly higher than zero on more than one axis, then maybe
>> indeed there is something wrong in the data, but I would suspect some
>> data handling error before I suspected a fault in the Shimmer itself.
>> Do the accelerometer plots look just like this in ShimmerConnect?
>>
>> Likewise for the magnetometer, which will always show the Earth's
>> magnetic field pointing in some direction, unless you put the Shimmer
>> in a thick iron case.
>>
>> Hope this is helpful,
>> dale
>>
>>
>>
>> On 1/19/2015 3:16 PM, Weiguang guan wrote:
>>> Hi Shimmer users,
>>>
>>> I'm a new user, and run into a weird problem --- I got non-zero
>>> acceleration and magnetometer values from Shimmer sensors even when
>>> they are totally static. Below are two plots (x, y, z components are
>>> in red, green and blue respectively) made from a very simple
>>> experiment where only a linear motion without rotation and there are
>>> static periods at both the beginning and the end. Have you run into
>>> problem before? Please drop a line if you know what happens. Thanks.
>>>
>>> Best,
>>> Weiguang
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Shimmer-users mailing list
>>> Shimmer-***@eecs.harvard.edu
>>> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>>
>

[Weiguang guan]

Hi Shimmer users,

This morning I played with a single Shimmer3 sensor and watched the
plots of magnetometer x, y, z (all CAL) on the fly. I placed the sensor
on a table, and slowly rotated it while keeping one of its face in full
contact with the table surface. I found one of the axes (which is Cal Z)
remained roughly constant so I believe the Z axis points up. What
confused me is that the other two components are mostly negative during
the rotation, especially one of them never had a positive value no
matter how much I rotated it.

How to explain this? Even if some electrical device in the room had
impact on the local magnetic field, the combined field (with earth
magnetic field) should point to certain direction. I would very much
appreciate it if someone could shed a light on the confusion. Thank you
very much.

Best,
Weiguang

[Dale Roberts]

You are correct in your expectation that if you rotate the Shimmer 360 degrees, you should generally see both positive and negative numbers on the X and Y axes due to the Earth's magnetic field. There are a few possibilities I can think of.

1) Maybe you are making an error in handling the data in Matlab. Run ShimmerConnect, enable the Magnetometers, and see what numbers you get there on the screen. I just did that, and Z stays relatively stable, and X and Y RAW values both go above and below zero. The raw sensors may be "unsigned", in which case you may have to subtract an offset to get properly "signed" numbers.

2) If you do indeed have a large magnet very nearby (like w/in a few cm of a neodymium magnet, or you are near an MRI machine!), the sensors can saturate and the sign may appear to change erroneously.

3) Your calibration is messed up. Collect a CSV file with ShimmerConnect. Open in Excel or some other spreadsheet. Look at both the RAW and CAL mag data. If the RAW X and Y signals are going positive and negative, and the CAL is not, then your calibration is no good.

dale

________________________________________
From: shimmer-users-***@eecs.harvard.edu <shimmer-users-***@eecs.harvard.edu> on behalf of Weiguang guan <***@rhpcs.mcmaster.ca>
Sent: Wednesday, January 21, 2015 2:47 PM
To: shimmer-***@eecs.harvard.edu
Subject: [Shimmer-users] Magnetometer puzzle

Hi Shimmer users,

This morning I played with a single Shimmer3 sensor and watched the
plots of magnetometer x, y, z (all CAL) on the fly. I placed the sensor
on a table, and slowly rotated it while keeping one of its face in full
contact with the table surface. I found one of the axes (which is Cal Z)
remained roughly constant so I believe the Z axis points up. What
confused me is that the other two components are mostly negative during
the rotation, especially one of them never had a positive value no
matter how much I rotated it.

How to explain this? Even if some electrical device in the room had
impact on the local magnetic field, the combined field (with earth
magnetic field) should point to certain direction. I would very much
appreciate it if someone could shed a light on the confusion. Thank you
very much.

Best,
Weiguang

[Dale Roberts]

... Sorry, I meant to go back and correct #1 below. The RAW values are in fact signed. So, if you were expecting them to be unsigned, then maybe you are subtracting an offset when you should not be.

dale

________________________________________
From: shimmer-users-***@eecs.harvard.edu <shimmer-users-***@eecs.harvard.edu> on behalf of Dale Roberts <***@jhu.edu>
Sent: Wednesday, January 21, 2015 3:47 PM
To: Weiguang guan; shimmer-***@eecs.harvard.edu
Subject: Re: [Shimmer-users] Magnetometer puzzle

You are correct in your expectation that if you rotate the Shimmer 360 degrees, you should generally see both positive and negative numbers on the X and Y axes due to the Earth's magnetic field. There are a few possibilities I can think of.

1) Maybe you are making an error in handling the data in Matlab. Run ShimmerConnect, enable the Magnetometers, and see what numbers you get there on the screen. I just did that, and Z stays relatively stable, and X and Y RAW values both go above and below zero. The raw sensors may be "unsigned", in which case you may have to subtract an offset to get properly "signed" numbers.

2) If you do indeed have a large magnet very nearby (like w/in a few cm of a neodymium magnet, or you are near an MRI machine!), the sensors can saturate and the sign may appear to change erroneously.

3) Your calibration is messed up. Collect a CSV file with ShimmerConnect. Open in Excel or some other spreadsheet. Look at both the RAW and CAL mag data. If the RAW X and Y signals are going positive and negative, and the CAL is not, then your calibration is no good.

dale

________________________________________
From: shimmer-users-***@eecs.harvard.edu <shimmer-users-***@eecs.harvard.edu> on behalf of Weiguang guan <***@rhpcs.mcmaster.ca>
Sent: Wednesday, January 21, 2015 2:47 PM
To: shimmer-***@eecs.harvard.edu
Subject: [Shimmer-users] Magnetometer puzzle

Hi Shimmer users,

This morning I played with a single Shimmer3 sensor and watched the
plots of magnetometer x, y, z (all CAL) on the fly. I placed the sensor
on a table, and slowly rotated it while keeping one of its face in full
contact with the table surface. I found one of the axes (which is Cal Z)
remained roughly constant so I believe the Z axis points up. What
confused me is that the other two components are mostly negative during
the rotation, especially one of them never had a positive value no
matter how much I rotated it.

How to explain this? Even if some electrical device in the room had
impact on the local magnetic field, the combined field (with earth
magnetic field) should point to certain direction. I would very much
appreciate it if someone could shed a light on the confusion. Thank you
very much.

Best,
Weiguang
_______________________________________________
Shimmer-users mailing list
Shimmer-***@eecs.harvard.edu
https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users

[Weiguang guan]

Dale,

Thank you again for the instant helpful response.

Regarding the 3 possibilities. 1) I actually used ShimmerConnect to show
the streamed Magnetometers on the fly, instead of plotting the data in
Matlab after data acquisition. 2) I will chose another location to run
the test again. 3) I will confirm this possibility by a test. Thank you
again for pointing out these likely causes of the problem. I'll share my
investigation once I have a conclusion.

Best,
Weiguang

On 21/01/2015 3:51 PM, Dale Roberts wrote:
> ... Sorry, I meant to go back and correct #1 below. The RAW values are in fact signed. So, if you were expecting them to be unsigned, then maybe you are subtracting an offset when you should not be.
>
> dale
>
> ________________________________________
> From: shimmer-users-***@eecs.harvard.edu <shimmer-users-***@eecs.harvard.edu> on behalf of Dale Roberts <***@jhu.edu>
> Sent: Wednesday, January 21, 2015 3:47 PM
> To: Weiguang guan; shimmer-***@eecs.harvard.edu
> Subject: Re: [Shimmer-users] Magnetometer puzzle
>
> You are correct in your expectation that if you rotate the Shimmer 360 degrees, you should generally see both positive and negative numbers on the X and Y axes due to the Earth's magnetic field. There are a few possibilities I can think of.
>
> 1) Maybe you are making an error in handling the data in Matlab. Run ShimmerConnect, enable the Magnetometers, and see what numbers you get there on the screen. I just did that, and Z stays relatively stable, and X and Y RAW values both go above and below zero. The raw sensors may be "unsigned", in which case you may have to subtract an offset to get properly "signed" numbers.
>
> 2) If you do indeed have a large magnet very nearby (like w/in a few cm of a neodymium magnet, or you are near an MRI machine!), the sensors can saturate and the sign may appear to change erroneously.
>
> 3) Your calibration is messed up. Collect a CSV file with ShimmerConnect. Open in Excel or some other spreadsheet. Look at both the RAW and CAL mag data. If the RAW X and Y signals are going positive and negative, and the CAL is not, then your calibration is no good.
>
> dale
>
> ________________________________________
> From: shimmer-users-***@eecs.harvard.edu <shimmer-users-***@eecs.harvard.edu> on behalf of Weiguang guan <***@rhpcs.mcmaster.ca>
> Sent: Wednesday, January 21, 2015 2:47 PM
> To: shimmer-***@eecs.harvard.edu
> Subject: [Shimmer-users] Magnetometer puzzle
>
> Hi Shimmer users,
>
> This morning I played with a single Shimmer3 sensor and watched the
> plots of magnetometer x, y, z (all CAL) on the fly. I placed the sensor
> on a table, and slowly rotated it while keeping one of its face in full
> contact with the table surface. I found one of the axes (which is Cal Z)
> remained roughly constant so I believe the Z axis points up. What
> confused me is that the other two components are mostly negative during
> the rotation, especially one of them never had a positive value no
> matter how much I rotated it.
>
> How to explain this? Even if some electrical device in the room had
> impact on the local magnetic field, the combined field (with earth
> magnetic field) should point to certain direction. I would very much
> appreciate it if someone could shed a light on the confusion. Thank you
> very much.
>
> Best,
> Weiguang
> _______________________________________________
> Shimmer-users mailing list
> Shimmer-***@eecs.harvard.edu
> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
> _______________________________________________
> Shimmer-users mailing list
> Shimmer-***@eecs.harvard.edu
> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>

[Weiguang guan]

Hi Dale,

It turned out the problem was caused by using the default factory
setting. After calibration, it works fine. Thank you for your time
helping me out.

Best,
Weiguang

On 22/01/2015 10:50 AM, Dale Roberts wrote:
> Great, I'd be curious to hear what the problem is!
> dale
>
> On 1/22/2015 9:21 AM, Weiguang guan wrote:
>> Dale,
>>
>> Thank you again for the instant helpful response.
>>
>> Regarding the 3 possibilities. 1) I actually used ShimmerConnect to
>> show the streamed Magnetometers on the fly, instead of plotting the
>> data in Matlab after data acquisition. 2) I will chose another
>> location to run the test again. 3) I will confirm this possibility by
>> a test. Thank you again for pointing out these likely causes of the
>> problem. I'll share my investigation once I have a conclusion.
>>
>> Best,
>> Weiguang
>>
>> On 21/01/2015 3:51 PM, Dale Roberts wrote:
>>> ... Sorry, I meant to go back and correct #1 below. The RAW values
>>> are in fact signed. So, if you were expecting them to be unsigned,
>>> then maybe you are subtracting an offset when you should not be.
>>>
>>> dale
>>>
>>> ________________________________________
>>> From: shimmer-users-***@eecs.harvard.edu
>>> <shimmer-users-***@eecs.harvard.edu> on behalf of Dale Roberts
>>> <***@jhu.edu>
>>> Sent: Wednesday, January 21, 2015 3:47 PM
>>> To: Weiguang guan; shimmer-***@eecs.harvard.edu
>>> Subject: Re: [Shimmer-users] Magnetometer puzzle
>>>
>>> You are correct in your expectation that if you rotate the Shimmer
>>> 360 degrees, you should generally see both positive and negative
>>> numbers on the X and Y axes due to the Earth's magnetic field. There
>>> are a few possibilities I can think of.
>>>
>>> 1) Maybe you are making an error in handling the data in Matlab. Run
>>> ShimmerConnect, enable the Magnetometers, and see what numbers you
>>> get there on the screen. I just did that, and Z stays relatively
>>> stable, and X and Y RAW values both go above and below zero. The raw
>>> sensors may be "unsigned", in which case you may have to subtract an
>>> offset to get properly "signed" numbers.
>>>
>>> 2) If you do indeed have a large magnet very nearby (like w/in a few
>>> cm of a neodymium magnet, or you are near an MRI machine!), the
>>> sensors can saturate and the sign may appear to change erroneously.
>>>
>>> 3) Your calibration is messed up. Collect a CSV file with
>>> ShimmerConnect. Open in Excel or some other spreadsheet. Look at
>>> both the RAW and CAL mag data. If the RAW X and Y signals are going
>>> positive and negative, and the CAL is not, then your calibration is
>>> no good.
>>>
>>> dale
>>>
>>> ________________________________________
>>> From: shimmer-users-***@eecs.harvard.edu
>>> <shimmer-users-***@eecs.harvard.edu> on behalf of Weiguang guan
>>> <***@rhpcs.mcmaster.ca>
>>> Sent: Wednesday, January 21, 2015 2:47 PM
>>> To: shimmer-***@eecs.harvard.edu
>>> Subject: [Shimmer-users] Magnetometer puzzle
>>>
>>> Hi Shimmer users,
>>>
>>> This morning I played with a single Shimmer3 sensor and watched the
>>> plots of magnetometer x, y, z (all CAL) on the fly. I placed the sensor
>>> on a table, and slowly rotated it while keeping one of its face in full
>>> contact with the table surface. I found one of the axes (which is
>>> Cal Z)
>>> remained roughly constant so I believe the Z axis points up. What
>>> confused me is that the other two components are mostly negative during
>>> the rotation, especially one of them never had a positive value no
>>> matter how much I rotated it.
>>>
>>> How to explain this? Even if some electrical device in the room had
>>> impact on the local magnetic field, the combined field (with earth
>>> magnetic field) should point to certain direction. I would very much
>>> appreciate it if someone could shed a light on the confusion. Thank you
>>> very much.
>>>
>>> Best,
>>> Weiguang
>>> _______________________________________________
>>> Shimmer-users mailing list
>>> Shimmer-***@eecs.harvard.edu
>>> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>>> _______________________________________________
>>> Shimmer-users mailing list
>>> Shimmer-***@eecs.harvard.edu
>>> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>>>
>>
>

[Weiguang guan]

Hi,

Does someone have experience with the Shimmer Matlab Instrument driver?
The official Shimmer website doesn't have a download link (least no
clickable download link). But I find one at

http://www.mathworks.com/matlabcentral/fileexchange/43712-shimmer-matlab-instrument-driver

Two questions:
1) Is it free of charge?
2) When someone uses the instrument driver to stream data in matlab, can
he use the Shimmer Conect in the same time?

Best,
Weiguang

[Jong Chern Lim]

Hi Weiguang,

Yes we no longer host the Shimmer Matlab Insrument Driver (files) on our
site, the link you posted below is the correct one.

1) Is it free of charge?
- The Shimmer Matlab Instrument Driver is but Matlab is not.

2) When someone uses the instrument driver to stream data in matlab, can
he use the Shimmer Conect in the same time?
- No. If you explained your use case I might be able to advice further.

I hope that helps.

Best regards,
Jong Chern


-----Original Message-----
From: shimmer-users-***@eecs.harvard.edu
[mailto:shimmer-users-***@eecs.harvard.edu] On Behalf Of Weiguang guan
Sent: 20 February 2015 03:07
To: shimmer-***@eecs.harvard.edu
Subject: [Shimmer-users] Streaming motion data live from Shimmer units

Hi,

Does someone have experience with the Shimmer Matlab Instrument driver?
The official Shimmer website doesn't have a download link (least no
clickable download link). But I find one at

http://www.mathworks.com/matlabcentral/fileexchange/43712-shimmer-matlab-ins
trument-driver

Two questions:
1) Is it free of charge?
2) When someone uses the instrument driver to stream data in matlab, can
he use the Shimmer Conect in the same time?

Best,
Weiguang
_______________________________________________
Shimmer-users mailing list
Shimmer-***@eecs.harvard.edu
https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users


-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2013.0.3495 / Virus Database: 4257/9143 - Release Date: 02/19/15

[Weiguang guan]

Hi Jong Chern,

Thank you for your time. Here I'm helping a research group with the
motion data acquisition, and I'll ask them if they need both in the same
time. I personally don't think it's necessary. Thanks again for
answering my question.

Best,
Weiguang

On 20/02/2015 1:37 AM, Jong Chern Lim wrote:
> Hi Weiguang,
>
> Yes we no longer host the Shimmer Matlab Insrument Driver (files) on our
> site, the link you posted below is the correct one.
>
> 1) Is it free of charge?
> - The Shimmer Matlab Instrument Driver is but Matlab is not.
>
> 2) When someone uses the instrument driver to stream data in matlab, can
> he use the Shimmer Conect in the same time?
> - No. If you explained your use case I might be able to advice further.
>
> I hope that helps.
>
> Best regards,
> Jong Chern
>
>
> -----Original Message-----
> From: shimmer-users-***@eecs.harvard.edu
> [mailto:shimmer-users-***@eecs.harvard.edu] On Behalf Of Weiguang guan
> Sent: 20 February 2015 03:07
> To: shimmer-***@eecs.harvard.edu
> Subject: [Shimmer-users] Streaming motion data live from Shimmer units
>
> Hi,
>
> Does someone have experience with the Shimmer Matlab Instrument driver?
> The official Shimmer website doesn't have a download link (least no
> clickable download link). But I find one at
>
> http://www.mathworks.com/matlabcentral/fileexchange/43712-shimmer-matlab-ins
> trument-driver
>
> Two questions:
> 1) Is it free of charge?
> 2) When someone uses the instrument driver to stream data in matlab, can
> he use the Shimmer Conect in the same time?
>
> Best,
> Weiguang
> _______________________________________________
> Shimmer-users mailing list
> Shimmer-***@eecs.harvard.edu
> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2013.0.3495 / Virus Database: 4257/9143 - Release Date: 02/19/15
>

[Weiguang guan]

Hi Jong,

The reason we want to stream data into Matlab the same time as we
collect data via Shimmer GUI is that we want to monitor multiple sensors
to make sure they function well during our experiment (In some rare
occasions, one sensor drops out or one channel of a sensor drops). Since
we can't use both in the same time, can we
(1) have data streaming on one computer to serve as a monitor, and data
collecting on another computer via Shimmer GUI? or
(2) customize the Shimmer GUI setting so that it displays more than 4
plots (so far only plots are shown)?

If we could stream synch-ed data from multiple sensors into Matlab, we
would plot and save the data all in Matlab. Can we synchronize them?

Best,
Weiguang

On 20/02/2015 9:44 AM, Weiguang guan wrote:
> Hi Jong Chern,
>
> Thank you for your time. Here I'm helping a research group with the
> motion data acquisition, and I'll ask them if they need both in the
> same time. I personally don't think it's necessary. Thanks again for
> answering my question.
>
> Best,
> Weiguang
>
> On 20/02/2015 1:37 AM, Jong Chern Lim wrote:
>> Hi Weiguang,
>>
>> Yes we no longer host the Shimmer Matlab Insrument Driver (files) on our
>> site, the link you posted below is the correct one.
>>
>> 1) Is it free of charge?
>> - The Shimmer Matlab Instrument Driver is but Matlab is not.
>>
>> 2) When someone uses the instrument driver to stream data in matlab, can
>> he use the Shimmer Conect in the same time?
>> - No. If you explained your use case I might be able to advice further.
>>
>> I hope that helps.
>>
>> Best regards,
>> Jong Chern
>>
>>
>> -----Original Message-----
>> From: shimmer-users-***@eecs.harvard.edu
>> [mailto:shimmer-users-***@eecs.harvard.edu] On Behalf Of Weiguang
>> guan
>> Sent: 20 February 2015 03:07
>> To: shimmer-***@eecs.harvard.edu
>> Subject: [Shimmer-users] Streaming motion data live from Shimmer units
>>
>> Hi,
>>
>> Does someone have experience with the Shimmer Matlab Instrument driver?
>> The official Shimmer website doesn't have a download link (least no
>> clickable download link). But I find one at
>>
>> http://www.mathworks.com/matlabcentral/fileexchange/43712-shimmer-matlab-ins
>>
>> trument-driver
>>
>> Two questions:
>> 1) Is it free of charge?
>> 2) When someone uses the instrument driver to stream data in matlab, can
>> he use the Shimmer Conect in the same time?
>>
>> Best,
>> Weiguang
>> _______________________________________________
>> Shimmer-users mailing list
>> Shimmer-***@eecs.harvard.edu
>> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 2013.0.3495 / Virus Database: 4257/9143 - Release Date:
>> 02/19/15
>>
>
> _______________________________________________
> Shimmer-users mailing list
> Shimmer-***@eecs.harvard.edu
> https://lists.eecs.harvard.edu/mailman/listinfo/shimmer-users
>