Data acquisition on the basis of time

Hi everyone,
I want to acquire the radial run-out (radial small displacement) of a rotating spindle using a capacitive sensor. To do so I will use the LabView v. 7.1. The PCI-6036E card from National Instruments (NI) will be utilized for data acquisition. The spindle turns at 100 rpm and a rotational incremental encoder is fixed at rear of spindle. This encoder provides an index digital pulse per revolution. This pulse should be used to start and finish the sampling process. I want to sample on the basis of time, by means of sampling rate of the card (Ksamples/s). So, let us suppose that I want to acquire 500 data/rev. The spindle takes 0.6 sec to complete one revolution. Thus, the required sampling rate is Fs = 500 samples/0.6 s = 833 samples/s. So, I should set the VI in LabView so that it samples only 833 data/s. Therefore, I will have to reduce the sampling rate of the analog-input channels in use. For example, let us suppose that the card provides 100 Ks/s when operating in multiple channels. Let us admit that there are 4 analog-input channels in use. So, the scan rate per channel is 25 Ks/s. This is too much for this application. I only need 833 samples/s. So, I should program the VI so that the card provides that required sample rate. As said earlier, I need to start and end the sampling process at the same point. Thus, to do that the index pulse of the encoder will be used. Also, I want to sample during 5 consecutive revolutions of the spindle. So, by means of a loop in VI, I should count the index pulse of encoder until the number of pulses be equal to 5 (= number of revolutions). At this instant, the sampling process should be stopped. Note: 1) the sampled data should be put in a buffer. After the sampling process is finished, this data should be saved in a file of LabView; 2) In fact, the data acquired by the sensor are voltage analog input. Questions:1) Could you make a VI for this problem, please? Note: you can use the DAQ ASSISTANT EXPRESS VI or DAQmx TASK NAME CONTROL method2) What should I do to stop the data acquisition at the end of 5 revolutions using the index pulse of encoder?3) Could you send examples (VIs) similar to my problem above? In anticipation, thank you very much for any help. My e-mail: [email protected]
Bruce

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Message Edited by smercurio_fc on 11-14-2008 09:10 AM

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Data type of the base attribute or the base value does not match...

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+<ERROR+
TEXT="'DWH.CUB_REGISTRATIONS_AW.REGISTRATIONS': XOQ-02517: Der Datentyp des Basisattributs oder der Basisgröße stimmt nicht mit dem zugeordneten Ausdruck überein.
XOQ-01400: Ungültige Metadatenobjekte"/>
The English message must be something like this:
The data type of the base attribute or the base value does not match the assigned expression.
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>
02517, 0, "The data type \"%(1)s\" of the base attribute or base measure is different from the mapped expression \"%(2)s\"."
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>
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I better explain my problem in the thread How to timestamp continuous analog data acquisition using USB-6009 and GPS timing board?
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Solved!
Go to Solution.

You have two options:
A. As you mentioned, you can place code inside your current while loop to do the processing. If you are clever, you won't need to place another while loop inside your existing one (nested loops). But that totally depends on the type of processing you are doing.
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Hi beam,
I just want to verify that I understand your situation correctly:
An external trigger signal (A) is wired to one of your input channels (e.g. CH0) to trigger data acquisition of a second channel (e.g. CH1). Your power meter is connected to an analog input channel, which you would like to trigger with a certain rising edge at some of your sequence structure.
Problem:
During a certain point in my data-acquisition sequence structure (defined by a frame), I want to use the next occuring analog trigger signal (A) to acquire 1 value from the power meter.
How do I do this in Labview programming for the following two situations?
a) If I connect the analog output from the power meter to an analog input channel of the 6036E DAQ card. The analog trigger (A) would be connected to a second analog input channel (In case the analog trigger signal (A) is changed to a TTL signal it would be connected to the PFI0/Trig input pin on the DAQ card).
If a task has been configured to acquire signal from one analog channel, it's not possible to run a second analog input task or to add a second channel on the fly. You had mentioned that it's possible to read from the instrument through GPIB. Is it possible to perform a software trigger such that at a certain frame of your structure, when the trigger signal A reaches voltage "x", a GPIB command is written to your power meter to query a measurement reading?
Additional questions:
How do I configure the PFI0/Trig pin on the 6036E DAQ board individually as an INPUT?
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How do I use an analog trigger signal (A) as counting signal for a loop, or as an activation signal for a sequence structure which includes GPIB commands?
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Attachments:
PXI5124-data-acquisition.vi ‏46 KB

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Data acquisition on the basis of time

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