Can fan controllers/monitors reliabily report fan speeds down to 100RPM?

I have a liquid flow meter that sends out pulses much like fans do.

Now it sends out 1 pulse per 10ml of liquid that flows through it. I need to be able to get a reliable reading on liquid flow rates down to 1 litre per minute, which if we do the math, equates to an effective fan speed of 100RPM. This is kinda nice, because if I saw, say, 432RPM, that would equate to 4.32 litres per minute.

I tried plugging the flow meter into my motherboard's fan headers, and get fluctuating readings which is undesirable. The sample period of the fan pulses seems to be too low. If I watch it for long enough I found that the highest value that it reports is the actual flow rate and it will fluctuate with values below that point.

What I wondering is if there are any of those fan controller/monitor devices out there which can reliably report fan speeds down to 100RPM? Anyone with any experience with seeing their unit being able to report such? Any help is greatly appreciated.

I've seen the ones in the BIOS which changed and would always be a multiple of 25..that was the onboard sensor, so I'd bet a fan controller would do a better job.

Also, what flow meter did you get?

ajrettke said:

I've seen the ones in the BIOS which changed and would always be a multiple of 25..that was the onboard sensor, so I'd bet a fan controller would do a better job.

Click to expand...

Yeah - that was the other thing. The mobo tended to report in multiples of 16RPM, which is also less than desirable. A 1RPM resolution is preferable.

Also, what flow meter did you get?

Click to expand...

It's a nutating flow meter, looking much like the sort of thing you see installed as water meters for houses. It's a positive displacement flow meter, meaning that it's almost totally viscosity independent (highly desirable). Big and bulky (~5.5" long x 4" diameter), but very low flow resistance (about equivalent to a 50cm length of 1/2" ID tubing).

Can read more about it here: http://www.aicpl.com.au/brochures/fs_ksm15.pdf