Role of Hysteresis Loop tracer / Watt-Loss Testing Equipment in Motor Industry

Electromechanical Devices like Motors, Pumps, Relays, Contactors etc. have two major constituents Copper and Magnetic core. Both have a major impact on the cost of the device and also on its performance.

Naturally to maintain quality in manufacturing or improving the performance by better design the properties of both these constituents play an important role.

Copper characteristics have little scope to improve upon. The quality of copper wire used to avoid faults like pinholes, porosity, oxidation, stresses etc is to be ensured.

For magnetic materials, however, the scope is much higher and essential as the range of properties available is vast. There are several magnetic parameters affect the performance of the device. Magnetic properties get affected even during the manufacturing process.

To keep the discussion short let us take case of typical devices like Motors or Pumps. Both are electromechanical devices. The conversion of electrical energy to mechanical work is affected by magnetic core characteristics. Both devices consume energy even when no mechanical work is carried out on the output (idle run or no load run) Also if the device is operated under various load conditions the conversion efficiency changes. Other factors that would affect the conversion efficiency are the frequency at which the device is operating. This same fact has to be considered when switch mode power supplies are used to run the device in which case waveform may constitute more than the basic desired frequency.

In short the magnetic core has to be understood completely to qualify for the operating conditions under which the device is going to perform.

Let us be more specific. What magnetic parameters affect the efficiency of electromechanical energy conversion.

Hysteresis Losses is obviously a straightforward answer but this requires little more in-depth understanding. We are elaborating this a step later.
Permeability is another parameter that affects the efficiency of the magnetic core.
Saturation Magnetization is the parameter that is a deciding factor for the size of the core for the optimum performance of the final product.

Hysteresis Losses: The losses in the magnetic core are of two types. One Intrinsic hysteresis losses – these occur even under DC conditions and the second is eddy current losses- which occur due to the conductivity of the magnetic material. Both these losses are frequency dependent. The intrinsic losses depend linearly on frequency while eddy current losses depend on the square of the frequency. If hysteresis loop is measured at any given frequency the hysteresis curve and losses derived from it give a measurement of total losses intrinsic hysteresis plus eddy current losses. These losses depend upon the induction level and the frequency. In the magnetic materials the composition, conductivity, stress level, interlaminar insulation, lamination thickness all affect the losses.

Starting raw material and processes like decarburizing decide the composition. Processes like rolling, straightening, punching, handling, and transportation affect the stresses in the material. Processes like stacking, handling, welding, clitting affect interlaminar insulation and thus affect losses.

Permeability: is a direct measure of the magnetizing current required to generate given induction in the magnetic core. The larger the permeability the lesser is the magnetizing current. The current is a direct measure of the copper loss and thus affects the efficiency equation.

Saturation magnetization: decides the maximum induction level at which a device can be operated. The larger the induction level smaller can be the size of the final product.

It is easy to understand that the measurement and understanding of magnetic parameters like Saturation magnetization, Permeability, and Magnetic losses is very vital in designing and maintaining quality during the manufacture of Motors or Pumps.

These parameters ought to be measured in reference to the induction level and frequency of interest. The properties should be measured on the raw material as well as on stacks during the process of manufacturing.

It must be stressed that the measurements settle all the issues of quality while manufacturing and give you an edge to improve the product with advantage. This allows one to choose alternative core material with confidence. This opens an opportunity of utilizing cost-effective materials and gives easy escape at the time of crisis due to supply crunch.

In addition to the above benefits FERRITES INDIA Hysteresis Loop Tracer is a handy tool for designers and also for reverse engineers for fault or failure analysis.


The equipment can take measurements on strip samples using Epstein Square stack (covers measurements as per IS 649) as well as on samples in the form of toroids (covers measurements as per ASTM A912/A 912M-04). The system can take comparative measurements on Stator Stacks. can offer measurements at DC & frequencies up to 1kHz

The Equipment with options to choose from and (below) the test results obtained. Typical Results obtained on CRGO laminations in Epstein Square Stack. Plots of MH hysteresis curve (Red), Magnetization Vs Field(Green), Watt Loss Vs Induction (Blue) and Permeability Vs Induction (Pink) curves are shown.

Magnetic Test Report

Precision Metals Lmt., India
Date : 27 November, 2010 :16:13

Specimen Code : Vijai
Alloy System: crgoV
Prior Treatment : Comm
Reference : Method: Measurements using Epstein Stack

Data on Specimen used:
Mass : 349.9 gms
Length : 35.0 mm
Area : 0.327 sq cm


Tested by:

Instrument : FERRITES INDIA make S21 series Hysteresis Loop Tracer