DRV5056-Q1: DRV5056-Q1

Ali,

Thanks for reaching out with this question.  For speed and direction there are a few options. On method uses multiple Hall-effect latches 90 degrees out of phase to produce a quadrature output.  Depending on the order of the edge transitions, the direction can be determined and the frequency of the edge transitions will indicate speed.  A standard dipole magnet would only provide 90 degrees of resolution as there are 4 unique output conditions for one full pole pair.  This can be improved by using a multi-pole ring magnet.  Please consider TMAG5110 or TMAG5111 which integrate two orthogonal sensors into a single package.  This allows the sensor to detect field components of the magnet which are naturally 90 degrees out of phase and there for only one device is required.

https://www.ti.com/lit/ds/symlink/tmag5110.pdf

The TMAG5110-5111EVM demonstrates this function using included 10 pole and 20 pole magnets.

https://www.ti.com/tool/TMAG5110-5111EVM

Tips how to setup this type of sensor are in this document:

https://www.ti.com/lit/an/sbaa449a/sbaa449a.pdf

A second method uses two linear Hall-effect sensors to measure the field component as the magnet rotates, also with the sensors placed 90 degrees out of phase.  This placement will result in a sine/cosine output from the sensors.  These outputs can then be processed with the atan2 function to produce an absolute angular position.  This might be implemented using two DRV5055 devices along with a standard dipole magnet. An example of this solution can be found here:

https://www.ti.com/tool/DRV5055-ANGLE-EVM

Again, the component count can be reduced by integrating orthogonal elements into a single package.  TMAG5170 and TMAG5273 offer the ability to track the complete 3D magnetic field vector.  Using either of these devices allows for a single sensor to be placed near the magnet.  These devices also allow for gain correction to ensure the sine/cosine outputs have equal amplitude before generating an angle output directly.  

https://www.ti.com/lit/ds/symlink/tmag5170.pdf

https://www.ti.com/lit/ds/symlink/tmag5273.pdf

The EVM demonstrates this function as well

https://www.ti.com/tool/TMAG5170UEVM

And you can find guidance on this function here:

https://www.ti.com/lit/an/sbaa463/sbaa463.pdf

Thanks,

Scott

Ali,

Sure.  For TMAG5111 the device will need a series of alternating N and S poles.  The number of poles will set your overall resolution.  The simplest approach would be a single diametric magnet, like you have pictured above.  As the magnet rotates, you would see 4 output positions per revolution for this magnet.  To increase resolution, you might use a multi-pole ring magnet.  The tradeoff when increasing the pole count will be a reduction in magnetic field strength.

Since the BOP/BRP threshold is about 2.6 mT maximum for TMAG5111 it should be possible to use a wide selection of magnets.  In the case of the EVM, we included a 20 pole magnet which operates nicely.  In order to achieve higher pole counts, the radius of the ring would typically need to increase in order to maintain a large enough area per pole.

Thanks,

Scott

Ali,

1. BOP is the operating point, the magnetic field must exceed this value in order to cause the output to change states.  Then for BRP, the release point, the field must return below this point in order to return to the default state.  In the case of a latched device, you will typically see BRP = -BOP.  That is if the operating point is 2.6 mT, then the release point will be -2.6 mT.  This can be particularly useful for a magnet rotating about it's own axis of symmetry.  You will want a magnet with a field strength at your sensor location greater than 2.6 mT.  Depending on which side of the magnet is presented to the sensor, the direction of the vector will be either positive or negative and cause output transitions.

2. In your above picture, the number of poles is 4, given you have two diametric magnets. The ability to detect each pole will depend on the orientation of the magnets.  The Latch needs to detect alternating poles in order to properly function. The poles of the magnets in your case should be oriented tangentially and not radially towards the center of the reel. Additionally, what you will see with the above arrangement is that there is a large region where there will be little to no input to the sensor.  In effect, you will only be able to detect 1/2 rotations of the reel. As each magnet passes over the sensor, you should be able to determine the direction of travel using TMAG5111 as the two axes produce output transitions out of phase from each other. 

3.NdFeB magnets tend to have stronger magnetic fields, and SmCo magnets tend to be more stable over temperature.  Either would likely produce sufficient magnetic field for the sensor. 

4.   If you need greater resolution than 1/2 rotation, then you might consider a flexible magnetic tape strip with alternating poles or a larger number of magnets.  As the number of pole transitions increases, the ability of the sensor to detect rotation will improve.

Thanks,

Scott

Ali,

All magnets are inherently dipoles.  Multi-pole magnets are essentially an arrangement of multiple dipole magnets fused together.  The magnet you pictured above is a diametric magnet, meaning the pole orientation is aligned along the diameter of the magnet.  This type of magnet if aligned tangentially could provide you direction information if used along with TMAG5111. The sensor would detect the two components of the field which are out of phase as it passes.  The order of the output transitions would provide directionality for you.

A simpler approach which assumes that you already know the direction of rotation is to just use a single Hall-effect switch, like DRV5032 along with an axial cylinder magnet.  This type would have the polarity as shown here:

One benefit is that you may use a switch that is sensitive to both Positive and Negative fields, and the magnet installation will be of less concern.  Additionally, there is a tool available on the DRV5032 product page which can help you determine if your chosen magnet and range are appropriate:

We also have a downloadable excel tool which can help you determine the field about various magnet types as needed.  You can enter the magnet properties and dimensions and it will help calculate the field at specified locations.  You could check range on an axial magnet using the head-on approach and could check a diametric magnet passing over using the slide-by approach.  The latter is not a direct match to your format, but should be close enough to approximate.  

Magnetic Proximity Tool

I'd expect many of the magnets you have linked to would work fine for this application. While these are diametric, they could still be used with DRV5032 provided that the magnet is aligned properly.  If the DRV5032DU were selected, you may still be able to determine direction based on the order of the output transitions.

Thanks,

Scott

Ali,

Sure, no problem.  To use TMAG5110 or TMAG5111 you will have two axes each sensitive to a different axis.  If we think of your setup as a flattened 2D sweep, we would see the two magnets passing somewhat similar to this with diametric magnets facing the same direction

Here if the magnets are facing the same relative orientation the X channel should always see the same direction vector, though if placed close enough to the magnet there is a small region where a negative magnitude exists for a short time.  Here you would just track the Z output to sense the reel.

It would be more useful to orient these opposite to each other

In this setup the outputs will follow a normal quadrature pattern, though we will see two state changes per magnet.  From here you should be able to tell which magnet edge was the last detected. The pattern of edges will also indicate the direction of rotation.

If you choose to orient the magnets with the pole vertical, we would see another pattern emerge.

This is a slightly more difficult arrangement to use to track the speed and direction, but it might be used as well.

Thanks,

Scott

Ali,

You will need either XZ or YZ.  Whether X or Y is appropriate will depend on the device rotation as laid out on the PCB.  You'll just want to be sure the horizontal component matches your layout.

Ali,

Yes. You've got it.

Scott