Speed Sensor--Max current for the counter input on my 6221 (Power supply question)

[Ralph@NES]

Hello all,

I've been doing some searching and reading about speed measurement for a while.  I've got my sensors located and got my VI planned, and generally have a clue.

The one thing I'm not sure of is the actual power supply to use.

Sensor will be a Cherry Corp geartooth sensor with a TTL-type output with a pull-up resistor, 0-5v.  I know where to connect it on my 1180 feedthrough panel.  What I have read on here is that some people have 'fried' their inputs by using too high a current, and I'm wondering what kind of power supply (obviously 5vdc) and amperage would be best.

Ideally, I'd like to jump directly from my computer's power supply--which of course have a 5vdc output.

Sound reasonable or do I need a solution with a low MA output?

Thanks in advance!

[Wayne.C]

I've done a lot of work with speed pickups.  What model # of speed pickup have you selected?

[Ralph@NES]

I was leaning towards the GS1005002 on this page:

http://www.cherrycorp.com/english/sensors/gs1005_1009.htm

I'm not really tied to that, I just have a lock nut with four notches in it that would make a handy 'gear' and pretty much any geartooth sensor would work fine.  These sensors work with 5-24v.  I'm not sure if the output amperage is tied to the power supply amperage, or if it's regulated by the sensor--either way, if there's a better geartooth sensor for interface with NI, I'm all ears.  I have to have it ordered today and implemented no later than Thursday though.

FWIW, actual RPM is not a major concern of mine right now--it will be in future tests--this sensor will simply be used to detect if a shaft has stopped spinning due to failure of a coupler rather than motor shutdown. 

Timely responses are appreciated IMMENSELY!  Thanks!

[Wayne.C]

Took a look at datasheet and crunched a couple of quick numbers.  Max load on your 5V supply will be 16.64mA. 

Sensor is specd to have a max current draw of 6mA.  Recommended external pullup is 470 ohms when using 5V supply.  Worst case current draw will occur when output transistor inside sensor is on and full 5V is being dropped across the 470 resistor.  That means that 10.64mA of current will be flowing through the 470ohm resistor and the sensor will be drawing 6mA to power itself for a total of 16.64  You just need to verify that the supply you use can source that much current at 5V.  Depending on how you are using the rest of your digital I/O, 6211 may be able to supply the 5V.  See the spec sheet for more details.  .   http://www.ni.com/pdf/manuals/371932c.pdf

If you use a supply other than the 6211, make sure it is properly referenced to the 6211.

0-5V signal to your counter is exactly what you want.

There are some high output speed pickups that generate large ac signals that can damage hardware.

Good luck and let me know how you make out.

[Ralph@NES]

6221, not 6211.

If I can use the DIO to provide the reference, that's great.  All I have running on the system now is my 1102 for thermos and a 1125...  I think...  Switch module.

If I were to use the card to provide the reference voltage, what would the wiring scheme be?

You're being extrememely helpful, and thanks!

[Wayne.C]

Are you using this in a PCI version?

[Ralph@NES]

Yes, it's the PCI-6221.

http://digital.ni.com/manuals.nsf/websearch/254F7B95B52A8287862572210058A786

I also have the SCXI-1180 Feed through panel with a terminal block to access the connections...

http://digital.ni.com/public.nsf/allkb/B2889ADCFD4B915986256E830081790F

So connecting to the DAQ directly should be easy.  Just wondering what channel to use, how to wire it and grounding, etc...

Is that sensor a good choice in your opinion?

[Wayne.C]

Spec says 5V supply on 6221 is good for 1 amp.  More than enough for your application.

Power connections:

Connect 6221 +5V signal to sensor VCC signal.

Connect 6221 D GND signal to sensor ground signal.

( Note: Strongly advise using twisted/shielded cable for connections to sensor. )

The signal will then be connected to which ever digital input is configured as the counter input.  You determine this either in MAX or in your VI.

This sensor should work just fine.  Just don't forget to hookup external pullup resistor.

[Ralph@NES]

Ok, that's what I was thinking...  Just wanted to make sure there was no grounding or weirdness involved.

I made a couple magnetic sensors before with the pull-up and tested them with a VOM so I'm good there.  Just needed some verification and details, and you helped immensely! 

I'm off to order my sensors, and THANKS!