Creating a High-Channel-Count, PC-Based Test System for Compressor Testing Using NI LabVIEW and Fieldbus

Author(s):
B. Sudha - Soliton Technologies Pvt. Ltd.
M. Jeyaselvan - Elgi Equipments Ltd.
Anand Prasad Chinnaswamy - Soliton Technologies Pvt. Ltd.
J. Rajeswari - Soliton Technologies Pvt. Ltd.

Industry:
Automotive, Research, Machines/Mechanics

Products:
FOUNDATION Fieldbus, PXI/CompactPCI, LabVIEW

The Challenge:
Providing a cost-effective data acquisition and control system with highly flexible software for performance evaluation of compressors.

The Solution:
Developing a cost-effective and user-friendly computer-based system using National Instrument products.

The Need for a Flexible, Automated System

ELGI Equipments Ltd. is the market leader and Asia’s largest manufacturer of air compressors and automobile service station equipment. As a part of company’s vision and strategy in becoming a leading player in the world market in its core products, ELGI required flexible and reliable test systems for design validation of its compressor products as per various standards, such as ISO1217, BIS1517, and IS10437. ELGI was using a semiautomated test rig based on a programmable logic controller (PLC) for compressor design validation. However, the capabilities of this system were limited and demanded manual intervention for system control, data analysis, and interpretation. As a result, ELGI approached us to build a flexible and automated system to test different compressor models

System Description

The compressor testing involved measurement of various critical parameters from nearly 70 channels from the compressor and various subsystems, such as performance test bed, lubrication system, air inlet and discharge system, and flow bench. We created a solution based on the NI PXI platform. The system acquired high-speed signals, such as torque and speed, using an NI-PXI 6052E high-speed data acquisition (DAQ) card. As the total number of channels was high, we used NI FieldPoint for the low-speed signals, such as temperatures, pressures, humidity, and flow rates. This effectively lowered the cost per channel by nearly half compared to other alternatives. We used FieldPoint analog input modules to acquire low-speed signals, such as pressures, humidity, water flow, oil flow, and air flow. We used the NI FP-AO-200 current output to actuate the valves. We used the NI FP-RTD-122 RTD input modules for temperature measurements from 27 locations in the test rig. We also used NI FP-DI-301 digital input and NI FP-DO-401 digital output for digital line control, such as valve positions, lamps, buzzers, and safety lines. A PC located in a control room provided the user interface, running the customized application software developed in NI LabVIEW. The PXI and FieldPoint modules were kept near the test rig, and using an NI MXI-4 interface, we had the flexibility to locate the PC in a separate control room.

We developed the application software in LabVIEW, and it contained configuration, calibration, run test, and data analysis modules. We developed the configuration module with high flexibility so the user could select the required channels or groups of channels for acquisition. Configuration set up files could be created with ease by using templates, thereby minimizing test set up times. The sampling rate, averaging, and display rates are defined by the user as initial configuration parameters. Finally, we provided a calibration module for calibration of all channels.

The run test module was the main module for data acquisition and display. The user could modify any combination of channels to be monitored, change tolerances, and units even during run time. This was very useful for the R&D setup, as it allowed for evaluation of test parameters under varying conditions. The system dispayes a graphical mimic for each subsystem based on the compressor model during run time. The run time software module displays the measured and calculated parameters on the corresponding schematic (as per the sub system selected).

A typical test begins with speed control and monitors various test parameters after steady state (or convergence). The test system controls a variable speed drive to set the motor speed and monitors the discharge pressure as it actuates the valve to reach the required discharge pressure. The system then goes to a convergence mode where various user-defined parameters are monitored for convergence within the defined tolerance. At any time during test cycle if any of the parameters exceeds the safety limits the test system was set to safely shut the test and generate alarms.

The system provided a wide range of user selectable parameter combinations, including multiparametric displays, in both graphical and tabular display formats. Online FFT analysis was provided for sound and vibration analysis. Using LabVIEW, we provided such extensive display options at ease, minimizing development time. One of the challenges was to acquire all data in less than 100 mSec and display the same online. Using the seamless integration of different types of NI hardware and the software, we flawlessly acquired and displayed both high-speed and low-speed signals.

We developed a detailed postanalysis module to review all data acquired during run time, trend analysis on the various performance characteristics, and generate detailed reports with graphical and tabulated outputs.

System Benefits

Comparison Parameter	Earlier System	Computer-Based Automated System
Functionality	Functionality limited to slow speed acquisition and elementary display	Provided all the functionality required by user – including high- speed and low-speed acquisition, online graphical display, and comprehensive analysis features
Ease of Use	PLC system was not user friendly and required manual intervention for data collection and control	PC-based system provided total automation of data acquisition and control without need for human intervention
Development Productivity	Involved ladder logic programming that was difficult and time consuming	LabVIEW provided quick development and deployment with superior functionality and performance
Reliability	With regular manual intervention, reliable results could not be obtained	PC-based system provided error- free and repeatable data acquisition
Test time	Test time was spread to two days	Test time is four to five hours
Data Representation and Analysis	Primitive display options and analysis features	Excellent graphical and tabular displays with options to store based on various criteria; Detailed review options provided comprehensive data analysis

NI-Based System Saves Development Time and Money

The PC-based system was easy to use and improved test productivity drastically. With no human intervention, the NI-based system was highly reliable and repeatable. Using LabVIEW, we implemented this complex application software in a short span of time. The seamless integration of hardware and software ensured quick deployment. The customer was delighted at the overall performance of the system, as it ideally suited their R&D requirements. The customer is now a true believer in the power of virtual instrumentation.

For more information, contact:

B. Sudha

Project Leader

Soliton Technologies Pvt. Ltd.

# 683, 15^th Cross Road,

2^nd Phase, JP Nagar,

Bangalore- 560078,

India

Tel: +91 -80- 51208600

Fax: +91 -80- 51208700

Email: sudha@solitontech.com

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