DSA-TIO Rotating Machinery Data Acquisition in CVI

This program performs a continuous analog data acquisition from a DSA board based on a trigger issued by a 6602 counter timer board via the RTSI bus. The 6602 board simultaneously starts a continuous buffered counting operation to acquire the tachometer input connected to a counter gate.

Principle:
This example allows you to perform acquisition of signals coming from rotating machinery vibration or noise.

The basic principle is to take advantage of the analog and digital anti-aliasing filtering available in the PCI 4451/52 and NI 4551/52 DSA boards, along with the delta sigma converters' linearity and oversampling to acquire high quality data from sensors used in rotating machinery applications. The idea is to acquire at a selected sampling rate and keep track of the shaft position by also acquiring a tachometer signal.

Once both signals are acquired, you will have an array with the time domain data acquired from up to 4 analog input channels, and you will also have an array of time stamps. Each timestamp element represents the elapsed time since the beginning of the acquisition or the previous stamp and each encoder pulse.

These two arrays of data can be very helpful in relating the vibration information to the shaft speed or position.

Encoder Acquisition or Time Stamps:
The encoder pulses are acquired through a PCI-6602 digital board, which has two NI-TIO timer counter chips and allows you to perform buffered counting operations. The NI-TIO chip is programmed to perform a buffered counting operation. The counter will count pulses coming from an internal timebase that can be 100 kHz, 20 MHz or 40 MHz, depending on the accuracy needed. Each time a rising edge is detected on the GATE input of the counter, the current count will be transferred to a buffer in the host memory.

The buffered counting operation will start based on an external digital trigger. This feature can be used to start at a desired shaft position. You can connect the INDEX of your encoder to this trigger input to start at 0 degrees. Then the A or B pulses of your encoder can gate the time stamp to produce an element in the array indicating the moment that each pulse was received.

Analog Acquisition:
The PCI 4451/52 or NI 4551/52 DSA board will be connected to the PCI-6602 board using a RTSI cable. A single buffered acquisition is programmed and starts when an external trigger is received on the 6602 board and transferred to the DSA board through the RTSI bus.

This way, both the analog and encoder acquisition start at the same time and the time stamps on the buffered counting array will be relative to the start of the analog operation as well.

Operation:
These examples will do an on-the-fly calculation of the RMP's of a rotating shaft based on the encoder input connected to the GATE of a counter on the PCI-6602 board. Once the shaft speed reaches a minimum selected test speed, the counters will be armed and the system will wait for a digital trigger to start the acquisitions. Once the trigger is detected, a continuous acquisition of the time domain waveforms on the DSA board and the encoder input on the PCI-6602 counters will be performed during a selected period of time.

At the end of the acquisition, two arrays will be available: one with the time domain data and the other with the encoder counts or time stamps relative to the start of the acquisition.

Requirements

Filename: dsatioc.zip

Software Requirements

Application Software: LabWindows/CVI Full Development System 9.0
Language(s): C

Hardware Requirements

Hardware Group: Multifunction DAQ (MIO)
Driver: Traditional NI-DAQ (Legacy) 6.5.2

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