Frequency measurement with PXI-6259

[danzimmer]

Hi!

I am configuring a new test system and we are using a PXI-6259 to make counter timer measurements.  My questions are pretty basic but I have no experience with the PXI-6259 and couldn't find my answers in the manual.

The PXI-6259 has two 68-pin connectors, Connector0 and Connector1.  Let's say that I want to measure the frequency of a signal.  The signal is routed to the PXI-6259 through 50 ohm coaxial switching.  It doesn't look like there are dedicated pins on the Connector for the counters.  Should I connect the signal to one of the Analog Input channels?  For example, would I connect the center conductor of the coax to AI 1 (Connector0 pin 33) and the outer conductor/shield to AI Ground (Connector0 pin 32)...then set the module up to measure frequency? 

Can I measure the time interval between two signals using the two onboard counters? For example, would I connect one signal to AI 1 and the other signal to AI 2?  Let's say that I want to start counting when the signal on counter 1 transitions through 2V on the rising edge and stop counting when the signal on counter 2 transitions through 0.8V on the falling edge?

We aren't using LabView or LabWindows software.  The software is another issue, and I'm really just trying to understand the basic hardware functionality right now.

Thanks!

Message Edited by danzimmer on 06-28-2008 03:08 PM

[Corby_B]

Hello danzimmer,

Thanks for your post and questions about using the PXI-6259! I Even though you are not using LabVIEW or other NI software to program your applications you will still need the DAQmx driver. This driver also includes a help file that talks about the pin outs for each card that the driver supports. So for your statement "It doesn't look like there are dedicated pins on the Connector for the counters." Its because the pins have a default value. Please see the picture of the pin outs for default pin assignments of the counters. The reason I say default is because if you want to route the signal coming in on a specific pin to another you have to see if this can be done in Measurement and Automation Explorer (MAX). MAX is used to populate all the information about all NI software and hardware you have on your computer. When you click on your device under NI-DAQmx devices there is a "Device Routes" tab that tells you what routs can be made internally and to what ports. Also if you right click on your device it will allow you to view pinouts, use test panels, reset device, etc. All the counter line default pins are on Connector 0.

Default NI-DAQmx Counter Terminals (Connector 0)

Counter/Timer Signal	Default Pin Number	Signal Name
CTR 0 SRC	37	PFI 8
CTR 0 GATE	3	PFI 9
CTR 0 AUX	45	PFI 10
CTR 0 OUT	2	PFI 12
CTR 0 A	37	PFI 8
CTR 0 Z	3	PFI 9
CTR 0 B	45	PFI 10
CTR 1 SRC	42	PFI 3
CTR 1 GATE	41	PFI 4
CTR 1 AUX	46	PFI 11
CTR 1 OUT	40	PFI 13
CTR 1 A	42	PFI 3
CTR 1 Z	41	PFI 4
CTR 1 B	46	PFI 11
FREQ OUT	1	PFI 14

So for instance if you wanted to count edges on counter 0 then I would connect your center conductor of the coax to the Gate of Ctr0 (PFI 9 pin 3) and the shield to D GND (pin 4).

So for your question about counting the different edges, the counter are based on TTL logic levels so anything above 3 volts is high and below 0.8 is low. So if you set up the counter to do two edge separation you can specify rising or falling edges to measure between.

Let me know if any of this helps you on your way and with your applications!

Cheers!

Corby_B
http://www.ni.com/support

[danzimmer]

Hi Corby,

Thanks for your reply!  I hope that you don't mind if I ask some follow up questions.

I downloaded a manual for the PXI-6259 from NI's website .  The section on DIO says that the 6259 has 48 DIO channels.  32 channels are on PO 0 through PO 31 and 16 channels are on PFI 0 through PFI 15.  So now I'm a bit confused because the pins that you said are dedicated to the counters are the same pins that appear to be used for DIO. 

I don't understand how the same pin can have two different functions.  For example, PFI 8 (pin 37) is CTR 0 SRC and CTR 0 A. 

Where can I find a description of the signal names?  For example, what is CTR 0 A, CTR 0 Z, and CTR 0 B?  I know that the counter has an A, B, and Z input, but what are these? 

Why would I input the signal on CTR 0 GATE?  Isn't that input for external gating?  Is the maximum input voltage into the counter +-11V?  What is the maximum frequency that the counters can measure? 

What is the input impedance of the counters?

'm sorry for so many questions, but I don't see what I need in the manual.  Thanks very much for your time and help!

By the way, the new test system will have LabView, which can be used for new applications.  One of the criteria for the system is that it run legacy test programs, and those programs are not written in LabView or LabWindows/CVI.

Dan

Message Edited by danzimmer on 06-30-2008 09:08 PM

[Corby_B]

Hello danzimmer,

Thanks for your post back and I would be happy to answer more of your questions!

So basically the pins that have both a PFI name and a port name can be used for both functionality. So for instance lets take Pin 37:

It is the ctr 0 source for using counter tasks.
It is PFI 8 when routing internal signals such as a sample clock to output on that pin.
It is also a digital P2.0 that can be used in digital tasks.

So this pin can only be used for one of these tasks at a given time but it gives you great functionallity. So for instance you only need 1 counter but need more digital lines. This way it doesn't reserve these pins for just counters and you can use other signals on them.

For all your counter questions I would refer to the M-series manual which talks about all the functionality of all the M-series cards. The A,B and Z lines are most commonly used for digital encoder tasks.

M Series User Manual

I would also like to recommend that you download the DAQmx driver. It is a free driver and once you have it you can open Measurement and Automation Explorer (MAX) and simulate the PXI-6259. This will allow you to write and test programs and especially test signal routing. There is a tab in MAX that is labeled "Device Routes" and will show you what routes the device can make internally to different pins. You can get the DAQmx driver from the following page:

Drivers and Updates

Let me know if this helps to clarify things for you and have a good day!

Cheers!

Corby_B
http://www.ni.com/support

[danzimmer]

Thanks, Corby.  Most of my questions were answered in the M-series manual.  I'll let you know if I need more help after I have time to read more of the manual.

Thanks, and have a great day!