PXI 4472 and MIO Analog Input Synchronization with Traditional DAQ

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Note:
This example uses Traditional DAQ VIs. We recommend the use of DAQmx VIs when working with these devices. See link below for a similiar example in DAQmx.
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This demo illustrates hardware synchronization between 4472s and E series MIO devices. This synchronization scheme was developed for an application monitoring 40 accelerometers and an E series card with SCXI for monitoring 32 thermocouples.

The synchronization is not as straightforward as synchronizing a pair of E series boards because the 4472 routes its oversample clock on the PXI-Star line, while the E series board uses a RTSI line for a sample clock. One of the general purpose counters on the MIO divides down and redirects the DSA oversample clock for the E series device to use.

The DSA oversample clock runs at 256 or 128 times the DSA sample rate, while the E series board requires a slower clock at the same frequency as the desired sampling rate. The counter's source is RTSI6, another name for the PXI-Star line carrying the DSA oversample clock. It divides this signal down by the correct ratio and outputs a slower MIO sample clock to a standard RTSI line. Because the divide down ratio can be any desired number, the MIO and DSA can sample at different rates while maintaining tight synchronization.

NOTE: This synchronization scheme will not work for DSA and MIO in the PCI form factor because the PCI DSA boards use a special RTSI line that counters cannot recognize.


Using the Software:

- Make sure your PXISYS.INI file is configured correctly. To do this, launch MAX and go to Devices and Interfaces. You should see your PXI-4772 on the device list. Highlight the 4472 located in Slot 2 of the PXI chassis. Look in the frame on the right side of the screen, which lists the PXI Slot. The slot should appear as "2". If it appears as "0", you may have a problem with the PXISYS.INI file (or it is absent). If you are using a PXI controller, copy the appropriate PXISYS.INI file to the top level of the Windows or WINNT folder. If you are using MXI-3, please refer to the related link below.

- Set the device numbers appropriately. If you have only one DSA board (the master in Slot 2) you should empty the array labeled "DSA Slave Devices".

- Fill in the array labeled "PXI Slot Numbers for DSA and MIO slaves." This array should contain the physical PXI Slot numbers for all DSA and MIO boards except the 4472 in Slot 2.

- Run the program. You should see time domain data from the DSA at 50 kS/sec and the MIO at 100 S/sec. (This is intended to represent sampling rates for accelerometers and thermocouples respectively.)

- If you change any of the sampling parameters, ensure that the value in "ratio of total acquired points" is a whole number. If it is a fraction, a scan backlog will slowly build on the DSA or MIO board, eventually producing a buffer overrun error. Setting the DSA and MIO at the same scan rate will always work without problems. You should have no difficulties when the sample rate of either the DSA or MIO is evenly divisible by the other.

Related Links:

KnowledgeBase 2CFE965P: Fix your PXISYS.INI file

KnowledgeBase 3EE7N2NQ: Synchronizing DSA Devices with DAQmx

Requirements

Filename: dsa_mio_input_sync.llb

Software Requirements

Application Software: LabVIEW Full Development System 6.0
Language(s): LabVIEW

Hardware Requirements

Hardware Group: Multifunction DAQ (MIO)
Hardware Model: PXI-4472, DAQCard-6023E
Driver: Traditional NI-DAQ (Legacy) 6.9.0

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