# Calculating Magnetic Flux Density inside a DC motor with a Hall Effect Sensor

#### Juan Andrew Sasongko

Joined Dec 4, 2017
18
Hi,

I'd like to calculate magnetic flux density inside a DC motor with a Hall Effect Sensor.
Which formula I can use? And could you please explain the formula for me?
Thank you!

#### Alec_t

Joined Sep 17, 2013
14,408
Welcome to AAC!
There is no single magic formula. Read the datasheet for the specific Hall sensor you intend to use, to see how its output relates to field strength.

#### Juan Andrew Sasongko

Joined Dec 4, 2017
18
Welcome to AAC!
There is no single magic formula. Read the datasheet for the specific Hall sensor you intend to use, to see how its output relates to field strength.
But is it possible to read magnetic flux density in a motor DC with only hall effect sensor?

#### Alec_t

Joined Sep 17, 2013
14,408
Yes, if you use a Hall sensor with an analogue output. e.g. something like this.

#### Sensacell

Joined Jun 19, 2012
3,501
The question is where would you place it?

The place where it matters (the air gap between rotor and stator) is way too small for any hall sensors I know of.

#### Juan Andrew Sasongko

Joined Dec 4, 2017
18
Yes, if you use a Hall sensor with an analogue output. e.g. something like this.
The question is where would you place it?

The place where it matters (the air gap between rotor and stator) is way too small for any hall sensors I know of.
Yes I believe. I was given a task to build a magnetic field meter with hall effect
My question until now is where do I place the sensor?
I was thinking about using hall effect sensor to measure voltage (by converting from RPM) and using ampere meter
Other said to remove the rotor and do the measurement, and find the effect of measured B in a stator to B in a whole motor. (But I think this case the hall effect will not be proportional with the direction of flux which causes the reading would be less accurate)
Do you have any idea?