Customer Solutions

Parallel Testing Pneumatic Modules Using LabVIEW and SCXI

Author(s):

Keith Brainard, Bloomy Controls Inc.

Industry:

Industrial Controls/ Devices/ Systems

Product:

LabVIEW, PXI/CompactPCI, Signal Conditioning

The Challenge:

Reducing manual procedures involved with testing electro-pneumatic modules to increase test throughput and reliability.

The Solution:

Automating module testing and reporting while also incorporating parallel testing capabilities.

A Connecticut manufacturing company that builds a variety of electro-pneumatic modules for instrument control applications often tests large quantities of modules as quickly as possible. To test the modules for air pressure leaks, the company previously used a system that required an operator to make multiple manual connections before a computer could read data from pressure transducers. This labor-intensive process involved great detail and invited error due to operator fatigue. To eliminate operator intervention at this level meant a dramatic reduction in the test procedure and an increase in its reliability. The company contracted National Instruments Select Integrator Bloomy Controls in Windsor, CT, to automate this process.

Combining NI LabVIEW and SCXI for digital I/O and analog input, we created an application where the operator sets up the module under test, starts the test, and forgets about it until the test is complete. The LabVIEW application runs on a standard Dell Pentium IV PC with an NI PCI-6024E data acquisition (DAQ) device in it. The DAQ device connects to the SCXI chassis, which contains the modules needed to communicate with the many signals involved on this stand. LabVIEW provides a pleasing, simple graphical user interface as a front end to an advanced system architecture.

The graphical user interface prompts the operator to enter the part number for the module or unit under test (UUT). Next, the software selects the appropriate test routines to run on the UUT. Using high channel-count SCXI, the software automatically performs the testing using digital relays and analog input for pressure transducers. The total system involves 148 digital relay channels used to open and close blocker valves, which an operator previously performed manually. Seventy-seven pressure transducers monitor pressure within the module, collecting data needed for leak rate analysis. With this many channels, SCXI was a clear choice.

Parallel Tests Performed with NI LabVIEW and SCXI
To help the company meet its high demand for product throughput, we implemented a parallel test system. The system features dual test stations, each capable of running tests asynchronously from the other. Tests executing on the two stations run at their own pace without interfering with one other.

To facilitate parallel testing, two asynchronous processes must share access to the same set of SCXI hardware. Supporting this structure requires a client-server architecture running on the test system PC. A server virtual instrument (VI) regulates access to the hardware. The server is responsible for all instrument communications and is always running. The server is the top-level VI that launches the client VIs – one for each of the two parallel test stations.

The program uses queues to communicate between the server and the clients. A command queue serves as a way for the clients to request data from the server. A string placed on the queue encodes the command to execute, the channel to read or write, and the data value to write (if applicable). In addition, the server uses a set of data queues, one for each client, to send data back to the client requesting data. Data queues use strings to pass data, which are interpreted as the appropriate data type by the client receiving the data.

Based on how the program is written, the company can easily expand the client-server architecture to handle more than two clients. Currently, only the number of channels in the SCXI chassis connected to the computer limits the number of test stations to two.

Operators Easily Run Data and Reports
As each test runs, the system stores information such as raw data values and results calculations. This information is stored to a tab-delimited file for easy import into spreadsheet programs such as Microsoft Excel for offline analysis. The system organizes data files in a structure that facilitates easy identification of a set of data and convenient retrieval for later analysis.

After operators complete a set of tests on a module, a results summary screen displays that the operator can choose to print. The print sheet includes each test name, test limits, measured values, and test results as well as information to identify the module tested and an overall summary of its Pass/Fail status. Otherwise, the operator can choose to close the screen without printing, saving unneeded paperwork and maximizing efficiency of the entire operation.

System Pays for Itself with Improved Throughput
The company originally had a 40-minute test for one module that required a high level of operator attentiveness to the test steps. With the test system from Bloomy Controls, the operator only has to load the module into the test station. Test time for this module was cut by 85 percent to 6 minutes. The test times for two additional modules were cut by 80 percent, with one test reduced from 15 minutes to 3 minutes and another reduced from 10 minutes to 2 minutes.

In addition, the parallel test stations enable an operator to load one test station while the other station is runs a test. During test time, the operator is free to perform other job-related tasks.

The company expects the improved throughput levels to provide a “break even” on the equipment investment in less than one year.

For more information, contact:
Keith Brainard
Bloomy Controls Inc.
839 Marshall Phelps Rd.
Windsor, CT 06095
Tel: (860) 298-9925