WEBENCH® Tools/DRV425: Simulation, hardware & system design tools forum

Hello Divyanshu 

1. 2mT = 2 milli Tesla this is the magnetic field measurement unit. The DRV425 only measures magnetic field in the axis shown in the datasheet. A current will generate a magnetic field as described in the document I forwarded to you. So you will measure a field based on the current and distance from that current. The shape of the conductor also matters as seen in that document a hole is place in that conductor to measure a larger current without saturating the DRV425 which is about 2mT.

2. If you are measuring current then you will need to make sure that you have the distance. For a circular conductor you can use the calculation described in the document. Then to translate that current you can use the DRV425 System Parameter Calculator to get the voltage the DRV425 given the Rshunt chosen.

Tools:

DRV425 Bus Bar Application Magnetic Field Calculator  Excel tool that lets you see the magnetic field seen by the DRV425 based on the dimensions of the bus bar, orientation of DRV425, and hole size and shape of the hole.

DRV425 System Parameter Calculator:  Parameter tool for the DRV425.  This is for an individual DRV425 and for general use not specifically for the bus bar.

DRV425 Bus Bar FEMM Script:  Script to generate a 2d model of a bus bar with a slot.  When you download this you will be able to see the instruction that are attached in a PDF and run the script (.lua file)

If you are measuring the harmonics of the motor like mentioned in the previous IEEE paper I sent this will be different as here you are more concerned with the harmonics from the leakage flux of the system and not current measurement. If you are measuring the harmonics of the current this may be difficult as the fundamental may be much higher than the harmonics.

3.Please elaborate on what you are trying to measure. I don’t understand.

4.I am not sure what your ultimate goal is. Are you attempting to measure the current or get the health of the motor?

Hi Sir,

We are looking for motor diagnostic and in that we are working on 2 options vibration and signature analysis.

Signature analysis

1.The problem which we are facing is to measure current we need wireless system to keep over the closed motor in such a away it can help us with the data to tell about the motor health.

Now i am using DRV425 to measure current through magnetic field after getting some point for healthy motor and same data will be capture for faulty motor and will find the harmonic determining the fault stage in motor.

2.But with this sensor i am not getting much useful data because how will i determine if peak current of motor is 2 amp and its taking above 2 amp i need to generate the alarm that can be done using wired connection but wirelessly am also trying with it.

3.Any suggestion for motor diagnostic in terms of current.?

Hello Divyanshu,

Measuring current vs measuring the motor health can be seen as two different issues. 

Motor health is looking at the leakage flux.  You may need to increase the Rshunt to measure lower fields as the case of the motor shields most of the magnetic field.  Here you are looking and comparing harmonics vs the fundamental frequency.  This is covered in more detail in the IEEE paper.  https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7590101

Measuring current is more about the location of the sensor relative to the current source.  This is more relative to the location of sensor with respect to the current source.  Here you could saturate the device and not see what you are looking for as the primary current fundamental frequency may dominate your signal and you may not be able to clearly see  harmonics

For motor health I would look more at the leakage flux and not the actual current.

Hi sir,

1.Measuring current is more about the location of the sensor relative to the current source. what actually it means location of sensor? can you please tell

2.Is DRV 425 is suitable sensor to move with magnetic flux leakage.? 

3.Harmonic approach is good to move with motor health or u can suggest something better.?

Hello,

1.  The sensor location inside the DRV425 is described in the datasheet.  Also the axis of sensitivity.  Where you place this relative to the current source will determine the magnetic field you will sense.

2. I do not understand.  The DRV425 will sense the magnetic field that is present in the axis of sensitivity.  When observing the leakage the axis is not as important because you are measuring everything relative to the fundamental frequency.  There will be spots around motor that have higher leakage and orientations that produce larger fields.

3. I believe from what I have seen that motor health can be observed with this as the paper was written.  This can be simple and easier to implement.

Dear Sir,

Exactly now i will place my DRV425 sensor where the possibility of leakage will be more in the system and check the flied around it.

1.How the below data is useful. Like i get some value near to 0.12 v of mt 0.1. What significance will it tell.?

2. Or we need to find the data for normal motor (taking values of weeks) and then compare the faulty motor with normal motor to find the harmonic difference.?  pic 1

3 How OR and Error can be useful because much of explanation is not given in datasheet.

pic 1

Hello Divyanshu,

Please attached photo another method as I cannot see it.

1.  If the signal is not strong enough you may need to increase your Rshunt.  Just be careful that the DRV425 does not saturate will all the magnetic field it sees.

2.  The IEEE paper is the best information I have on this subject.  Sorry I cannot see the information you provided.

3. If you increase your Rshunt value and cause the input to the Differential amplifier to go above |VRef/4| this will cause OR alarm to, note VS is a factor in this as well.  The OR alarm is when the differential amplifier is saturated.  The ERROR flag is when the flux gate is saturated so much that the internal excitation of the flux gate sensor cannot compensate for external magnetic fields meaning the field is too strong to determine the field and the output is invalid.

Dear Sir,

Attached is the pic. I am referring to IEEE paper for it. 

1.Agreed on your part about increase in rshunt value. But as pic attached what does Icomp refer to the table.It is the compensation coil which is directly proportional to the input current. How this table is useful to get data fruitfully. Because in actual the total current of motor would be about 2 amp or more.How to correlate it with this table.

2.OR and Error pin should be kept on polling to read input from the sensor.? at the time of saturation

When this situation arise.? at the time of fault in motor.?