# Regarding Depth Calculation

Discussion in 'General Electronics Discussion' started by naseer39, Dec 28, 2011.

1. ### naseer39

11
0
Dec 28, 2011
Hi to everyone..

I am using a IMU triaxial sensor from MEMsense which gives Accelerometer,Magnetometer and Gyroscope data.I have calculated Pitch,roll and Heading.Now i need to calculate Depth, can any one help me out ??????????

Thanks in advance,
S.Naseer

2. ### OLIVE2222

690
25
Oct 2, 2011
Hi naseer39,

Welcome to this forum !
Already having calculated Pitch,roll and Heading do you feel that any of the IMU sensors is
able to help you in the deepth calculation ?

Olivier

Last edited: Dec 28, 2011
3. ### naseer39

11
0
Dec 28, 2011
Hi,

I have contacted Memsense but no reply from them.............

Regards,
S.Naseer

4. ### OLIVE2222

690
25
Oct 2, 2011
Hi,

My question was not linked to any IMU manufacturer. With any type of accelerometer,magnetometer and gyroscope do you feel that you can calculate the depth ?
What the final project will be? A model submarine?

Olivier

5. ### naseer39

11
0
Dec 28, 2011
Hi,

We are working on Borhole survey system . We need to calculate depth(distance) it
has travelled into the borehole.I also need a clarification whether we can calculate
depth(distance) by using these parameters.????

Naseer

6. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
Don't you lower this thing on a cable? Don't you take readings every certain distance down the hole?

Either a direct reading of the length of cable (which will give you the length of the hole) or that combined with the normal 3D maths you're presumably already doing to get the position in space of each point down the hole.

7. ### naseer39

11
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Dec 28, 2011
Hi Steve,

We are using cable for lowering our thing,but is it possible to calculate distance with Accelerometer and Gyroscope readings with out the reference of cable ???

Naseer

8. ### naseer39

11
0
Dec 28, 2011
Hi steve,

One more thing i forgot to tell that we are using a Winch to drop our thing in the borehole..

Naseer

9. ### OLIVE2222

690
25
Oct 2, 2011
Hi,

Sorry for the post bouncing, just want to find out if it was a homework. The IMU platform will only provide you attitude indications. To measure the depth you can use (a well calibrated) pressure sensor, maybe a ultrasound, radar or laser ranging equipment. This to have it independent.

Olivier

10. ### naseer39

11
0
Dec 28, 2011
Hi Olive2222,

So,it is not possible to calculate depth(distance) with IMU sensor.....Thanks for the information....

Naseer

11. ### OLIVE2222

690
25
Oct 2, 2011
Hi,

You welcome Naseer ! No, nor the depth, the distance, or the altitude.
Maybe having accelerations in known (or measured) time can act as depth indication, not a real measure however.

Olivier

EDIT:

Well you talk about survey not drilling, so maybe you can characterize the winch resistance and let the IMU fall till hitting the ground. Combined with the time you should be able to have reasonable precision.

Last edited: Dec 29, 2011
12. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
Well, in theory, a gyroscope and accelerometers form the basis of an inertial navigation system.

However, practically, it it may be difficult to resolve the small accelerations which take place as the probe moves down the hole with sufficient accuracy to determine depth.

13. ### daddles

443
3
Jun 10, 2011
You don't give any details about the accelerometer, but you say it's a three-axis device. Theoretically, you can integrate the acceleration data twice to get the displacement (see any freshman physics book). However, I'd imagine the results could contain significant errors over time unless you have good accelerometers. You can easily do some simulations with some computer programs to see how things might work.

But if you're lowering it on a cable, it seems to me that the simplest solution is to measure how much cable has gone out and correct for the stretch caused by the load and cable mass. No doubt there are many tens of commercial things that do this already on the market.

14. ### naseer39

11
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Dec 28, 2011
Hi ,

i need a small clarification i am getting values of acceleration in "g",can we calculate speed from the acceleration.I know the basic formula V=A*t but where can i get "t" from???
can u please help me out???????

Naseer

15. ### Laplace

1,252
184
Apr 4, 2010
The basic formula given is for a constant acceleration, and the "t" is for the duration of the acceleration. However, your package is unlikely to be subject to constant acceleration during its movement. In that case you need to integrate the A(t) function over the total duration with respect to the differential time in order to find V(t).

16. ### naseer39

11
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Dec 28, 2011
Hi Laplace,

Practically we dont have uniform time,then integration can give accurate readings?

Naseer

17. ### Laplace

1,252
184
Apr 4, 2010
Non-uniform sampling times are just another potential source of error that must be dealt with, along with sensor error and instrumentation offsets. You would need to manage the error budget carefully, since performing a double integration can magnify small errors into much larger error.

18. ### naseer39

11
0
Dec 28, 2011
Hi,

Can we calculate Heading direction of IMU Sensor travelling downwards? i have calculated Heading for object travelling horizontal(NED convention)by using Accelerometer and Magnetometer.It is working fine...I am unable to findout in Vertical Case..can any one help me out?????

Thanks,
Naseer

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