• posted
Hi,
I am not a mechanical engineer, and I got a bit confused about the
If I understand it correctly, a load cell is a force sensor that
requires physical contact. The force is being measured by converting
strain (in the sensor) into an electrical signal. The strain must be
generated by an object that is in contact with the sensor. Is this
correct ?
An accelerometer measures acceleration in units of m s^-2. Can it be
also used to measure a force?
Willy
• posted
In general, yes. There are of course more elaborate magnetic suspension/force balances that have been investigated for wind tunnel testing.
Force can be implied by applying Newton's Second Law, F = m*a.
• posted
Yes
Force can arise in several ways: a nut tightened on a bolt, for instance. Any way it is provoked, a load cell can be arranged to measure it.
The kinds of acceleration we are familiar with, every day are 1) putting the pedal to the metal - or stamping on the brake pedal, 2) Jumping off a building. If you stand on the penthouse parapet, you feel your weight, your feet get tires...etc., etc. This is a force felt from resisting the acceleration.
If you slip over the edge, your feet no longer hurt, and you don't feel your body weight.
If we arrange a simple accelerometer consisting of a mass on a spring, when we stand on the edge, the weight of the mass is pulling down, and registering 1g or 9.8 m/s2 or 32 feet per second squared.
When we step off, the weight springs back, and the accelerometer indicates no acceleration! No wonder you can get confused!
Anyway. there is a relation between force and acceleration which we label inertia. In the simplest form. the equation reads force = mass times acceleration If you use units like kg for mass, Newtons for force, and meters per sec per sec for acceleration, there are no scaling factors built in so you can say a force of ONE Newton goes along with a mass of ONE kilogram speeding up by ONE meter per second per second. The weight of an apple in your hand is about 1 Newton, about a tenth kilogram or a quarter of a pound.
Clear as mud now?
Brian W
• posted
Why would it read 0? That is silly. Don't they read the Earths acceleration rate? After all it is not in a perfect orbital path with 0 acceleration. you better re-calibrate that thing. It will make you crash into a planet you are freefalling towards, and accelerating into.
• posted
take a look at an aerobatic airplane if you can. They have g meters to measure acceleration. On the ground, they read 1 g.
If you hold a meter like that upside down, it reads -1 g. However, if you jump off a parepet, it reads 0 g.
Brian W
• posted
But when on the ground, they are not being accelerated at 1 G. They are "at rest" with Earth they are being accelerated at only the acceleration changes that occur in Earths orbit and maybe the solar systems orbit arond the Galaxy and maybe even a tiny bit for the Galaxys trip around the Universe. anyways... . such is surely not 1 G at all or we would be able to float when on the far side of the furthest point in orbit. If anything, on the ground should be the 0 acceleration rate. and 1 g-force constant. (not accelerated) 2 different things. :)
That is bad, as I said. you better re-set it for "real" acceleration changes or one day you will crash into the planet you are trying to land on since the accelerometer will not measure the freefall acceleration rate. :)

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