Trouble Getting Fast Frequency Measurements From GTX2200
Nathaniel G.
Ann Arbor, MI

Apr 26, 2010
5 Posts

Trouble getting fast frequency measurements from GTX2200

I have a GTX2200  in an NI PXI-1044 chassis.  

I have followed the user guide and set the gate time to 500/250us and trigger level accordingly (Fixed, .5V), but the max output I get is 100 Samples/second.    I have affixed a standard frequency reference, 10 MHz to Channel A.

Is there a test GUI I can use to see how fast it is acquiring samples?
Are there other tips, besides those in the user's guide, that I should follow?

Dale J.
La Verne, CA

Apr 26, 2010
10 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Nathaniel, what function are you using to measure the frequency?  The suggestions in the user guide are for measuring to an array - GxCntReadMeasurementArray().  Also mentioned in the manual: The maximum number of measurements depends on the CPU speed, system configuration and number application running at the background. See the GxCntReadMeasurementArray function on how to achieve high number of measurements.

Regards,
Dale

Nathaniel G.
Ann Arbor, MI

Apr 27, 2010
5 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Thanks Dale.

This is precisely the function I am using, and from which I pulled those gate/level settings.
The embedded controller is a 2.2 GHz P4, so I do not think CPU speed is the issue.  Can you at least confirm that you or others get higher frequency performance?

Dale J.
La Verne, CA

Apr 27, 2010
10 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Nathaniel,
I'll put a test bench together and let you know what I find.  Would it be possible for you to send me your code for review?

Regards,
Dale




*Changed by Moderator

Dale J.
La Verne, CA

Apr 28, 2010
10 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Nathaniel,
I duplicated your results and am working with engineering to resolve the issue.  I'll post a follow-up when I have something to report.

Regards,
Dale

Nathaniel G.
Ann Arbor, MI

Apr 29, 2010
5 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Thanks Dale.  I am going to post the code I used, which is almost identical to the examples in the Users Guide.  Is there a code block section in this forum?

SHORT CHANNEL = 0;
SHORT coup = GXCNT_COUPLING_DC;
SHORT imp = GXCNT_IMPEDANCE_50OHMS;
DOUBLE gatetime = .0005;
DOUBLE level = 0.5;
SHORT prescale_mode = 1;
SHORT status;
SHORT mode =

GxCntInitialize(2, &handle, &status);
check_status(status);

//Reset the board
GxCntReset(handle, &status);
check_status(status);

//Set Channel Coupling
GxCntSetChannelCouplingMode(handle, channel, coup, &status);
check_status(status);

//GateTime
GxCntSetGateTime(handle, gatetime, &status);
check_status(status);

//impedance
GxCntSetChannelImpedance(handle, channel, imp, &status);
check_status(status);

//coupling
GxCntSetChannelCouplingMode(handle, channel, coup, &status);
check_status(status);

//write freq channel
GxCntSetFunctionFrequency(handle, channel, &status);
check_status(status);

//prescale mode
GxCntSetPrescaleMode(handle, mode, &status)
check_status(status);

//enable continuous mode
GxCntSetAcquisitionMode(handle,
                    GXCNT_ACQUISITION_CONTINUOUS, &status)
check_status(status);

data_buffer = malloc(sizeof(DOUBLE) * samples);
DWORD dw_samples = 100;

//read measurement array
GxCntReadMeasurementArray(handle, data_buffer, &dw_samples, timeout, &status);
check_status(status);

free(data_buffer)

Nathaniel G.
Ann Arbor, MI

Apr 30, 2010
5 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Please let me know if I can provide any information that can help resolve this.

Nathaniel G.
Ann Arbor, MI

May 4, 2010
5 Posts

Re: Trouble getting fast frequency measurements from GTX2200

Dale,  let me know if we need to talk in person.  Should I open a M@GIC ticket?


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