# How to estimate the load on a synchronous motor using a magnetometer sensor?

Hala Helmi
Looking for any insight on a formula that can be used to calculate the load using a magnetometer sensor for synchronous motor

Staff Emeritus
Synchronous motor load is proportional to the angle between the rotor poles and the rotating magnetic field in the stator. Angle can also be expressed as phase difference.

If you had a compass needle mounted on the outer perimeter of the rotor by at the pole, out would point in the direction of the rotor angle. So it it's the direction of that magnetic field, not the magnitude.

• Lnewqban
Hala Helmi
Many thanks anorlunda,
Is the increase in the load will affect the magnetic field ?
if it is possible can you help me to write the formula

Last edited:
Staff Emeritus
Can it measure direction?

Staff Emeritus
If you can measure the rotor angle ##\theta##, the equation for power will then be ##P=P_{max}\sin\theta##.

Where ##P_{max}## is a constant dependent on the details of the grid and the load and the wiring and the voltages.

• Lnewqban
Hala Helmi
Can it measure direction?
yes, it can measure the direction

Hala Helmi
Synchronous motor load is proportional to the angle between the rotor poles and the rotating magnetic field in the stator. Angle can also be expressed as phase difference.

If you had a compass needle mounted on the outer perimeter of the rotor by at the pole, out would point in the direction of the rotor angle. So it it's the direction of that magnetic field, not the magnitude.
Hi @anorlunda, I just want to check if I have a synchronous servo motor is this will make any difference

Staff Emeritus
It applies to all kinds of synchronous motors.

But there is a lot of engineering needed to measure that angle with a magnetometer. But in principle it is possible.