Using Labview/SCXI to measure rpm via magnetic sensor?

[Ralph@NES]

Hello All!

Here is what I'm trying to do... 

My current configuration is PCI-6221 into a SCXI-1001 Chassis with a 1349 Cable Adapter.  The only modules I have in this chassis right now are a 1102/b/c with a 1303 terminal block and a 1180 feedthrough with a 1302 terminal block.

I need to obtain a signal from a magnetic sensor of some variety (reluctance I'm assuming) and convert it to an RPM measurement. 

What we are doing is testing failure of bearings at 12,000 RPM.  My requirement is to take RPM measurements from the bearing CAGE (the metal part inside the bearing that prevents the balls from impacting each other) and accurately enough that when the cage fractures and the inscribed 'diameter' grows, that I can measure the RPM drop and shut down the system.

This bearing will be in oil and as such, we have no optical way of doing this.  At the moment I'm pretty sure a magnetic solution is the only that will work, and my questions are as follows:

1.  Can someone recommend a magnetic sensor that will be friendly to connect to my SCXI system?

2.  Will I be able to connect these sensors via the 1302/1180 to my PCI DAQ or will I need another terminal block and SCXI Module?

3.  Any proven or recommended setups for doing precise RPM monitoring via SCXI?

Any input is greatly appreciated, I need to have equipment purchased and on it's way in a few days.

[stilly32]

Hi,

This is going to depend a lot on the sensor and unfortunately I have no experience with magnetic sensors. I can point you to a couple resources though. Most of the magnetic sensors I have found info on generate a TTL pulse that you then measure the frequency of. Here are a couple links on that -

Using a Magnetic Encoder in an Anti-Lock Braking Application

I have a magnetic pick up sensor

How do I measure RPM from a magnetic pick up?

If you use a sensor that generates a TTL signal, you'll want to use the counters on your 6221 to measure the frequency of the signal. If you wanted to keep the SCXI system in the loop, you'd probably want to use the feedthrough module.

Hope this helps,

Andrew S

Message Edited by stilly32 on 05-02-2007 09:31 AM

[Ralph@NES]

Thanks for that input!

It would likely be a TTL signal, although reluctance is possible (if that's the case then it would need internal processing to filter the reluctor wave to a square TTL style wave).

I do have the 1180 feedthrough panel and a terminal block for the front of it.  Am I going to be able to connect this sensor (actually there will be eight total sensors on eight separate locations) directly to it if it's a 0-5v application?

And most importantly, will this be considered an analog input signal or a digital one?  The 6221 has 16 analog ins...  But only shows 2 counter/timers!

I'm thinking I'm going to need that 1126 module to do eight locations, correct?

[stilly32]

With 8 signals, the 1126 is going to be fine - it can read a square wave, so you're TTL signal will work.

Andrew S

Continued here