# Measuring dc motor parameters

As you are familiar with the principle of a DC motor or DC machine that when it is loaded either as a motor or as a generator, conductors of the rotor are carrying the current. To better understand the concept, imagine the conductors which are laying in the magnetic field which is present in the air gap. Due to that magnetic field each of the conductor experiences an electromagnetic force. Obviously due to the impact of that force conductors which is laying near to the surface of the rotor and also having the common radius from the center of the rotor, the torque is produced.

Since the torque produced is applied at the circumference of the rotor it causes the rotor to start rotating. In order to understand the torque, we should refer to the explanation of Dr. Huge d Young where he states that the torque is the quantitative measure of the tendency of a force to cause a rotational motion, or a force to bring about a change in rotational motion.

It is in fact the momentum of a force that produces or changes a rotational motion. The equation of torque is given by. Where, F is force in linear direction. Now if we talk about a DC motor which also works on the same principle since it is also a rotational machine. Understanding of the torque of DC motor is a very important in order to understand its operational parameters and its speed control etc. So we can say that in order to understand the running behavior and implications of any type of torque DC motor we must deeply look at the torque equation of a DC motor.

In order to have better understanding of torque motor equation below are given the basic circuit diagram of a DC motor. Therefore, torque equation of DC motor becomes as below by multiplying both sides of above equation 2 by I a.

Since I a 2 R a is the power loss due to heating of the armature coil. True effective mechanical power to produce the desired torque of DC machine is given by. The mechanical power P m is related to the electromagnetic torque T g as below:. Till this point of our exercise of finding the actual torque of a DC motor we have obtained the electromagnetic torque.

Next stage is to subtract all the mechanical and rotational losses from it to get the mechanical torque. So simplified form of the torque equation is given below:. Hope you have got good idea about the torque machine equation.

Now lets see a little about torque control of a DC motor. The speed control of induction motor is done using direct torque control with four switch three phase inverter.

The switching technique used is space vector modulation technique. The two phases are connected to the two legs of the inverter, while the third phase is connected to the mid point of the dc-bus voltage. Stator flux linkage is estimated by integrating the stator voltages. Torque is estimated as a cross product of estimated stator flux linkage vector and measured motor current vector. The estimated flux magnitude and torque are then compared with their reference values.

I am really thankful to the blog owner for help us by giving valuable study materials. I used to be recommended this web site by my cousin. I am now not certain whether or not this publish is written by him as nobody else realize such distinct about my problem. Sharing is caring:. Like this: Like LoadingDocumentation Help Center. The DC Motor block represents the electrical and torque characteristics of a DC motor using the following equivalent circuit model:.

You specify the equivalent circuit parameters for this model when you set the Model parameterization parameter to By equivalent circuit parameters. The resistor R corresponds to the resistance you specify in the Armature resistance parameter. The inductor L corresponds to the inductance you specify in the Armature inductance parameter. You can specify how to generate the magnetic field of the DC motor by setting the Field type parameter to the desired option.

The permanent magnets in the motor induce the following back emf v b in the armature:. The motor produces the following torque, which is proportional to the motor current i :. The DC Motor block assumes that there are no electromagnetic losses. This means that mechanical power is equal to the electrical power dissipated by the back emf in the armature. Equating these two terms gives:. As a result, you specify either k v or k t in the block parameters.

If the magnetic field is generated from the current flowing through the windings, the Back-emf constant depends on the field current I f :. The torque-speed characteristic for the DC Motor block is related to the parameters in the preceding figure. For the steady-state torque-speed relationship, L has no effect. The block uses the rated torque and no-load speed values in the preceding equation to determine values for R and k t. The resulting torque across the block is:.

It is not always possible to measure rotor damping, and rotor damping is not always provided on a manufacturer datasheet. An alternative is to use the no-load current to infer a value for rotor damping. For no-load, the electrically-generated mechanical torque must equal the rotor damping torque:. The value for rotor damping, whether specified directly or in terms of no-load current, is taken into account when determining equivalent circuit parameters for Model parameterization options By stall torque and no-load speed and By rated power, rated speed and no-load speed.

The block has an optional thermal port, hidden by default. This action displays the thermal port H on the block icon, and exposes the Temperature Dependence and Thermal Port parameters. Use the thermal port to simulate the effects of copper resistance losses that convert electrical power to heat.

Electrical conserving port associated with the DC motor positive terminal. Electrical conserving port associated with the DC motor negative terminal. Mechanical rotational conserving port associated with the DC motor case. Mechanical rotational conserving port associated with the DC motor rotor.

System Identification Toolbox DC motor

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Wound — Generate the DC Motor magnetic field using the current flowing through the windings. By equivalent circuit parameters — Provide electrical parameters for an equivalent circuit model of the motor.Based on the DC motor speed response measurement under a step voltage input, important motor parameters such as the electrical time constant, the mechanical time constant, and the friction can be estimated.

A power series expansion of the motor speed response is presented, whose coefficients are related to the motor parameters. These coefficients can be easily computed using existing curve fitting methods. Experimental results are presented to demonstrate the application of this approach.

In these experiments, the approach was readily implemented and gave more accurate estimates than conventional methods. DC motors have wide applications in industrial control systems because they are easy to control and model. For analytical control system design and optimization, sometimes a precise model of the DC motor used in a control system may be needed.

In this case, the values for reference of the motor parameters given in the motor specifications, usually provided by the motor manufacturer, may not be considered adequate, especially for cheaper DC motors which tend to have relatively large tolerances in their electrical and mechanical parameters. General system identification methods [ 1 — 4 ] can be applied to DC motor model identification.

In particular, various methods have been applied to DC motor parameter identification; that is, [ 56 ] used the algebraic identification method, [ 7 ] used the recursive least square method, [ 8 ] applied the inverse theory, [ 9 ] used the least square method, and [ 10 ] applied the moments method. Without expensive testing apparatus and a long testing cycle, a quick and effective system identification approach based on the motor input and output is desirable and valuable, especially for the field applications and quick controller prototyping.

In this paper, a DC motor parameter identification approach based on the Taylor series expansion of the motor speed response under a constant voltage input is presented. The relationships between the motor parameters and the coefficients of the Taylor series are established. In the implementation, the motor speed response under a constant voltage is sampled, then fit the samples to obtain the coefficients of power terms in the Taylor series.

Then, the DC motor mechanical and electrical time constants, back-EMF, and the friction can be computed using these coefficients.

### Electric Motor Power Measurement and Analysis

With the knowledge of these parameters, a precise motor model is obtained for the subsequent controller design. The curve fitting can be performed using many existing methods, such as the least square method, and these optimization methods are widely available in commercial computing packages such as Matlab and LabVIEW.

Consider the following DC motor governing equations: where is the motor speed, is the motor terminal voltage, is the winding current, is the back-EMF constant of the motor, is the torque constant, is the terminal resistance, is the terminal inductance, is the motor and load inertia, and is the disturbance torque. According to 1the velocity response in the Laplace domain is where is the electrical time constant, is the mechanical time constant, and is the Laplace variable.

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Based on these equations, we would like to know, and so forth, by measuring the velocity response under a known, controlled voltage input.

In this paper, we consider two application situations: the first situation is that the disturbance torque is negligible, while in the second one, the disturbance needs to be considered. When the voltage speed response dominates; for example, the input voltage is large, we can ignore the disturbance torque in the speed response see 3.

In this case, we can consider the following DC motor model:. The transfer function can be factorized into where. Assumption 2.Electric motors are electromechanical machines that convert electric energy into mechanical energy.

Despite differences in size and type, all electric motors work in much the same way: an electric current flowing through a wire coil in a magnetic field creates a force that rotates the coil, thus creating torque. Understanding power generation, power loss and the different types of power measured can be intimidating, so let's start with an overview of basic electric and mechanical power measurements. What is power?

In the most basic form, power is work performed over a specific amount of time. In a motor, power is delivered to the load by converting electrical energy per the following laws of science.

In electrical systems, voltage is the force required to move electrons. Current is the rate of the flow of charge per second through a material to which a specific voltage is applied. By taking the voltage and multiplying it by the associated current, the power can be determined. A watt W is a unit of power defined as one Joule per second. The power factor is a unitless ratio ranging from -1 to 1, and represents the amount of real power performing work at a load.

For power factors less than unity, which is almost always the case, there will be losses in real power. This is because the voltage and current of an AC circuit are sinusoidal in nature, with the amplitude of the current and voltage of an AC circuit constantly shifting and not typically in perfect alignment. This would be typical of a simple resistive load.

In this situation, the two waveforms are "in phase" with one another and the power factor would be 1. This is a rare case, as almost all loads aren't simply perfectly resistive. Two waveforms are said to be "out of phase" or "phase shifted" when the two signals do not correlate from point to point. This can be caused by inductive or non-linear loads. In this situation, the power factor would be less than 1, and less real power would be realized. Due to the possible fluctuations in the current and the voltage in AC circuits, power is measured in a few different ways. Real or true power is the actual amount of power being used in a circuit, and is measured in watts. Digital power analyzers use techniques to digitize the incoming voltage and current waveforms to calculate true power, following the method in Figure 1.

In this example the instantaneous voltage is multiplied by the instantaneous current I then integrated over a specific time period t.

## How to Calculate Torque of DC Motor?

A true power calculation will work on any type of waveform regardless of the power factor Figure 2.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts.

It only takes a minute to sign up. I appreciate if somebody could help me to resolve this. I bought a geared DC motor from a store. I would like to obtain the following information: Resistance, Inductance, Back EMF constant, torque constant, and the voltage caused by Back EMF when the motor is supplied by a voltage input higher than the recommended one. What is the best method to measure these parameters?

Do I need fancy equipment to get these values by experiments? Even I asked the company, they can only provide the following information at the recommended voltage : torque constant, Back EMF constant, Dynamic Resistance and Motor Regulation. The guy asked the manufacturer. He said that these are all he can get and he has no idea what they mean. Which parameter s stay the same? To measure back emf, depending on motor type, disconnect the wires!

The scope will also make it really easy to determine motor speed. If it is a brushed motor, I think this may not be appropriate. Another option to at least get an idea, and anyway useful for any design, is to monitor the voltage and current at the same time. You'll need some kind of current probe.

A current sense transformer and a resistor can be a quick option, if not just construct a small value sense resistor from many 1 ohm resistors in parallel. Consider thermal dissipation. If you do calculations, keep in mind also that the applied voltage as seen by the motor, back EMF, and current, are not necessarily in phase with each other, so you can't just go plugging peak values of your AC measurements into formulas to get a complete understanding of what's happening.

Also, if this is important enough and you can spare a motor, consider removing the gears for the purposes of any measurements. The torque constant and the back EMF constant will not change with changing voltage.

Diagram based 3 wire 220v schematic wiring diagram

Motor regulation is the speed change resulting from a given load torque change. If the magnetic flux of the field is constant as with a permanent-magnet DC motor with a commutator, the torque vs speed relationship is quite linear from no-load speed to stalled torque. Dynamic resistance is likely just the DC resistance including the brush and brush-contact resistance. Sign up to join this community. The best answers are voted up and rise to the top.

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Home Questions Tags Users Unanswered. What is the best way to measure the following DC motor parameters? Ask Question. Asked 3 years ago. Active 2 years, 3 months ago. Viewed 2k times. Thank you. The winding resistance will be voltage divided by the current. Find the value which gives 0.Estimating the Parameters of a Hydraulic System. Estimating Parameters of a Battery. Estimating Transfer Functions and Process Models.

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Toggle Main Navigation. Videos and Webinars. Videos Videos MathWorks Search. Search MathWorks. Videos Home Search. Contact sales Trial software. Register to watch video.The given project demonstrates above example. It applies PWM to DC motor to vary its speed from min to max and max to min continuously and also measures following parameters. It is very easy to vary the speed of DC motor using arduino. Arduino can generate PWM on its analog output pin and when it is applied to DC motor, its speed varies.

So it is very simple and easy task. When motor completes 1 revolution, the sensor generates 1 pulse and such pulses are calculated by arduino to calculate RPM. So let us see how this is done. Internal photo transistor is pulled up by resistor R4. The collector output of the transistor is connected to digital pin 7 or arduino. RW pin is connected to ground. Sometimes a delay is provided to allow the motor to attain full speed. Thus when the motor rotates one full revolution, the slot passes through sensor gap.

Due to the slot in the wheel, the IR light falls on phototransistor. So transistor conducts and generates a negative pulse in collector output.

Thus each rotation of motor produces a pulse. To measure the frequency of this pulse first the ON time is measured then OFF time is measured and from this frequency is calculated as That is directly displayed on LCD.

Thus the given project varies the speed of DC motor and also measures it accurately. So one can note down motor speed in RPM at different voltage and pulse width in observation table for further needs. In DC motor speed testing, the PWM is applied to the motor and its duty cycle is varied from min to max.

Along with this, the applied voltage to the motor is also measured to see the motor speed at different applied voltage. Finally, after noting down all the values, the observation table is prepared for pulse width duty cycleapplied voltage and motor speed in RPM. Connect with Engineers Garage on Social Media. Search Engineers Garage.