Simon Bridge said:It is normal for different instruments to disagree - the same instrument, if it is sensitive, will disagree with itself when repeating the same measurement - if they are properly calibrated, though, they should agree to within their uncertainty limits.
If all measurements agree, it is usually suspicious.
Simon Bridge said:You don't use an accelerometer to calibrate other accelerometers. You should use the manufacturers specifications for calibration.
In general, you calibrate instruments using known values that you obtain by other means ... i.e. use known accelerations (measured using a stopwatch and an accurate ruler say). It helps to decide how accurate you need the measurements to be.
If you knew that one accelerometer was the most accurate - wouldn't you'd just use that one and not bother with the others?
I'm guessing you are using the accelerometers in a device like a phone - and you have different kinds of phone... is that correct?
Note: the most reliable accelerometer is the one that returns the same value most consistently each time for the same test... reliability is not always helpful: an accelerometer that has two readouts "accelerating" and "not accelerating" will probably be very reliable... ("reliable" can also mean "robust").
I would use a turn table to spin them at some precisely known radius and angular velocity, then compare their reading with the calculated centripetal acceleration. But note that you have to know the exact position of the actual sensor for this.Thien said:So, how can we know which intrument is reliable to calibrate the others?
Thank you for your response!A.T. said:I would use a turn table to spin them at some precisely known radius and angular velocity, then compare their reading with the calculated centripetal acceleration. But note that you have to know the exact position of the actual sensor for this.
I think that measuring the radius and angular velocity in a rotating setup is more reliable than accelerating the sensors along a linear track, to calibrate them.Thien said:I'm not clear about radius and angular velocity which you mentioned, can they be measured?
You would have to differentiate it twice, which for noisy data usually means fitting some smooth function.nasu said:How did you measure acceleration with a laser telemeter? Recorded position versus time and integrated to get acceleration?
Hi nasu!nasu said:How did you measure acceleration with a laser telemeter? Recorded position versus time and integrated to get acceleration?
I agree with you but I don't have equipment to do that..A.T. said:I think that measuring the radius and angular velocity in a rotating setup is more reliable than accelerating the sensors along a linear track, to calibrate them.
Hi Simon!Simon Bridge said:There is still the question of how accurate the measurements need to be ... for that matter, how different are they?
Are the measurements consistent within the manufacturers uncertainty limits?
Perhaps if we had an example of the data with a description of the measurement process?
However - the controlled situations suggested above should help calibrate the equipment.
You just left out a great deal of information - assume I have not looked at your setup and do not know what you are doing or what equipment you have.Thien said:Hi Simon!
The shaker is excited with a function generator and then the vibrating part is measured with three accelerometer. The ecart type depends on frequency and tension excitation. For example, the Analog device and the laser telemeter has 19% and 200% ecart type at 30Hz and 100Hz, respectively.
The acceleration is recorded in z-axis at the same time. To be more clearly, I want to measure precisely acceleration in z-axis at low frequency with a shaker. The accuracy could be less 10%.Simon Bridge said:You just left out a great deal of information - assume I have not looked at your setup and do not know what you are doing or what equipment you have.
It sounds like you have a machine for shaking something - what? how? What sort of shaking do you expect?
Are you trying to measure the acceleration in three different axes directions at the same time or just at random orientations about the thing being shaken or what?
19% and 200% of what? 30Hz and 100Hz what?
You still have not said how accurate you need them to be...
I think we've gone as far as we can without knowing what you are trying to do.
No, it doesn't change the frequency but it changes altitude of the acceleration.CWatters said:Is the mass of the accelerometer changing the frequency of the vibration?
Acceleration measurement is the process of determining the rate of change of an object's velocity over time. It is a measure of how quickly an object's speed is changing.
Acceleration can be measured using various instruments such as accelerometers, velocity sensors, and gyroscopes. These instruments use different principles to measure acceleration, such as changes in position, velocity, or angular velocity.
The most commonly used unit to measure acceleration is meters per second squared (m/s²). Other units include feet per second squared (ft/s²) and gravitational units (g's).
Acceleration measurement has a wide range of applications, including motion detection in smartphones and gaming devices, vibration analysis in machinery, and determining the performance of vehicles and aircraft.
Acceleration is directly proportional to the force applied to an object. This relationship is described by Newton's Second Law of Motion: F=ma, where F is the force, m is the mass of the object, and a is the acceleration.