Hall effect sensor

I'd like to use a Hall Effect sensor to detect 6 magnets on the outside of a
2.5" rotating cylinder. It rotates at 20 RPM resulting in 120 pulses per
minute (I'll calculate speed from this). This will be a damp environment so
a ferrous 'target' is not an option.

I have found small inexpensive ring magnets (with the S pole facing out)
that I can easily mount on the cylinder. I have NOT found small inexpensive
ring magnets that are magnetized diametrically (N and S are on the same
face).

There are many many types of Hall Effect sensors. Most need alternating N
and S fields: either with 2 opposite poled magnets, or with a single N/S
ring magnet.
Is there a type that can detect the coming and going of just a S field (the
field will never be totally absent)?

I found a Gear Tooth Sensor type that senses a ferrous target. Can I just
use the S facing ring magnet instead of the ferrous target?


TIA


.

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