Wiring - PXI-6624

[DL84]

Hi All -

I have an application that I need to make use of a counter, we chose the PXI 6624.  I'm pretty darn good with the rest of NI hardware, aside from counters FPGA and RF are the only lines I haven't used.  I'm running into some trouble understanding how to set up my leads on the 6624 and thought I'd ask on here.

I have a remote optical sensor (Monarch Instruments Model ROS) that I will need to monitor pulses on.  Its got 4 leads coming off of it, a common, a signal, a +V excitation(10V), and the cable shielding (ie common).  I'm also hooked up to a SCB-100 using their 100 pin flex cable.

The thing that I'm getting hung up on, each counter on the module has 10 pins assigned to it.  I keep going through the manual, but I'm having trouble understanding it.  Went to NI and the engineer there basically just copied and pasted the same part of the manual that I didn't understand.  When asking for more details, about the gate +/- for example the response I got was that "you can if you want to gate the signal you use the gate pins"...I assume that means you can use those pins as a switch to take the signal or not, like you would the Gate on a FET used like a switch.  Just an example of how detailed the responses are 🙂

Anyhow, I'm reading through and it sounds like each of the inputs almost has multiple functions that overlap, but I'm having trouble digesting it.  Can anyone help out with the wiring on this?

Just FYI - Short term, I have 1 sensor that will count RPM as 1 pulse per revolution.  We will also want to do direction which will require a second sensor with the two set up much like the quadrature function requires.  Only still both will have only 1 pulse per revolution, rather than an encoder with say 120 pulses per rev.  Will eventually need to wire up both, but I think if I can figure out just the one I can use that to figure out the rest of the setup on my own 🙂

Thanks a bunch!

[Wayne.C]

leachdor,

Because the inputs on the 6624 are isolated, it takes two connections for each input signal.  That's where the gate +/- , source +/- etc comes from.  Figure 3-3 in the manual explains this.  http://www.ni.com/pdf/manuals/372142a.pdf  

[DL84]

Two connections for each input signal?  Any circuit needs to have a + and return to ground to pass current, so you def need at least two wires going to each counter used.  Are you saying though that I need to branch my signal into two connections?  So signal wire would go to gate+ and source +, then gate- and source - would be common (also split to two leads from the sensor)?

[Wayne.C · Accepted solution]

External Connections: 

Sensor common connected to source - of counter

Signal from sensor connected to source + of counter

Any gate signal you would use for this application would be generated internally using another counter and then internally routed to the gate of the counter that is counting the external pulses.  In this case the gate signal would provide an accurate window of time in which to count pulses.  An example would be measuring RPM.  If you decide to measure pulses for an entire minute, how do you accurately define a minute?  If you don't count for exactly a minute, your RPM measurement will be incorrect.  Software timing won't work.

[DL84]

I'm following...

That will leave the excitation lead though.  So if I can get a 10VDC supply, I'll go from + on the supply to the excitation lead.  Does this also need to go the counter as a reference?  The sensor itself gives a negative pulse output signal, so looks like its always at 10V, then each time the sensor trips it sends a pulse at 0V.  Then the common of the sensor will go to both the - DC supply and - Source

[Wayne.C]

10VDC supply + connected to excitation of sensor.

10VDC supply - connected to sensor common and source - of the counter.

The fact that the inputs are optically isolated means that the counter does not need to be referenced in any way to the external 10VDC supply.

The negative going pulse is no problem because you can configure the counter to count on either the rising or falling edge of the source signal. 

[DL84]

Thanks for the help!

Need to set up a little fan or something to try this out.  I guess I just disregard the Vdd, Vss, Gate +/-, or AUX +/- ?

[Wayne.C]

You won't be using any functionality associated with the Aux+/-.  Vdd and/or Vss would get connected only if you were using a signal from a counter to drive one of the digital outputs.