Creating Reliable, Automated Test System for Switches and Sockets with NI LabVIEW

Author(s):
Mondeep Duarah - Captronic Systems Pvt. Ltd.

Industry:
Research, Electronics

Products:
FieldPoint, PXI/CompactPCI, LabVIEW

The Challenge:
Implementing an accurate, reliable, rugged, and programmable automated test system for batch testing of household switches and sockets, which operates continuously for 24 hours a day, spanning more than several days.

The Solution:
Developing the system using National Instruments PXI-8176 real-time controller, FieldPoint PXI-6527 digital I/O, PXI-6052E multifunction data acquisition (DAQ), and SCXI-1102B

Introduction

A leading manufacturer of household electrical switches and sockets for low-voltage application required an automated test system to perform various batch tests on switches and sockets for quality assurance. The components to be tested are mounted on benches with the help of fixtures and tests are performed. These tests were previously performed manually, which was tedious as test observation and the test data were also recorded manually. We used an NI PXI-8176 real-time controller and FieldPoint real-time based test system to introduce reliability and drastically reduced the human intervention during testing as all the interlocks were taken care and necessary action/s were initiated automatically if any anomaly was detected. We recorded the test data and generated the report from the logged data.

Tests Performed on Switches and Sockets: Endurance Tests

During endurance test, the system first moves a variac to set the voltage at which the test is performed; the voltage is different for different switch ratings. The system then turns the switches on and off through an arm actuated by pneumatic cylinders. The on and off time are user programmable. During the on time, the system acquires three phase voltages and calculates the power factor. The user sets and monitors the number of cycles the test runs. The three sets of loads available include 32/40A, 6/12/20A, and an incandescent lamp load. The user has the option to choose any of the loads at a time. The test control system detects if the load is improperly set and generates an alarm. We used the PXI-8176 real-time controller along with NI PXI-6527 digital I/O and SCXI-1102B analog mux to realize the endurance test system.

Resistance to Heat and Resistance to Aging

We perform resistance to heat tests by keeping the switches and sockets samples in an oven. We introduce the samples chosen from a batch of production into the oven for the user-specified duration. The oven temperature is kept at a user specified value. The temperature of the oven is continuously monitored and logged. Using NI FieldPoint, we created closed loop control of the oven temperature. We perform resistance to aging on another oven where samples are kept for a longer duration.

Temperature Rise Tester

We use a temperature rise tester to measure the rise in temperature around the socket pins with respect to the ambient temperature. In this tester, we mounted three sockets or switches and connected them in series. This tester carries an autotransformer whose output is connected to the sockets or switches in series. We placed thermocouples at appropriate position on the socket or switches so as to monitor the rise in temperature at these locations with respect to the ambient temperature over the time. The system performs this test at a constant current by controlling the autotransformer with a motor through FieldPoint in closed loop. In addition, the current with respect to time is monitored and logged.

System Configurations

Based on PXI-8176 and FieldPoint, we designed the system for switches and sockets to cater to five endurance test stations, two temperature rise testers, and two ovens. All nine systems can run simultaneously or in any combination independent of each other without interfering with the functionality of the other. The system performs data logging on the PXI controller and stores data acquired by FieldPoint in the PXI controller. In case link to the PXI controller is lost temporarily because of some unforeseen issue, the system logs   FieldPoint to its nonvolatile flash memory. Later, when connection is established, the system automatically transfers the data to the PXI controller through FTP.

The system controls the five endurance test panels through the PXI-8176 controller. The LabVIEW Real-Time 7.1 program running on the PXI controller calculates the power factor by capturing the voltage and current signal only when the switches are on. Because the voltage will exist even when the switch is off, we were successful in capturing the current and voltage signal only when the switches are on and calculate the power factor.

In case any switch fails during the test, the system shuts down with a visual and sound alarm actuated by the NI PXI-6527 digital I/O. The system also generates an alarm if the load setting is not as per requirement, and these alarms are stored. Finally, the system also handles other interlocks, such as current and power factor crossing limits.

We used two ovens to perform resistance to heat and ageing tests. NI FP-2000 real-time controller/interface controls the heaters in a closed loop. It also monitors the oven temperature. In case oven temperature shoots up above the shutdown limit, the sytem turns off the heater and generates an alarm. It also checks if the temperature rise and current drawn crosses the set limit. If any of these errors occur, the system is turned off with a message.

We used the FP-2000 controller/interface to control two temperature rise testers. Here, switches or sockets are mounted on a fixture and a constant current is passed through them. The system controls this constant current via a motorized variac. Real-time FieldPoint software monitors the rise in temperature. Software also monitors if there is any fluctuation in current due to switch failure. It also checks if the temperature rise and current crosses limit. If any of these cases occurs, the system is turned off with a message.

One of the exciting features of the system is that it has the intelligence to handle power shutdown. In case of power shutdown, the system will restart automatically when the power is restored and start from the state where it stopped without any human intervention. This occurs simultaneously for all nine systems. Another interesting feature of the system is that during weekends, the system is brought to a complete shutdown. When the system is restarted, it will start from the state where it stopped. This feature was very important as all the tests are of long duration.

Software

After logging on to the system, the user can select the test equipment type. The corresponding test equipment is displayed from where the user can start the test. The system transmits the configuration to the PXI-8176 controller and FieldPoint real-time system through TCP/IP. The host system provides a display screen for monitoring the test. During the test, the host receives continuous feed back from the PXI-8176 controller system. Of all the parameters, these values are displayed on the host system along with the set values. After the test is completed reports are automatically generated.

A Brief Description of Software Features:

Resistance to Heat

• Temperature control of the oven with on-off control action.
• Alarm condition monitoring – warning and shutdown limits.
• Oven temperature and ambient temperature monitoring and logging using time stamp
• Unique identification for UUT by giving a name to each test
• Test duration monitoring – display of elapsed time for a particular UUT
• Test over indication
• Unique identification validation for duplicate entry
• Graphical display of oven temperature
• Configurable data logging rate

Temperature Rise Test

• Controlling of current delivered by the autotransformer by controlling a motor attached to the autotransformer shaft
• Monitoring and logging of current, all the thermocouples used, and the ambient temperature with time stamp and configurable logging rate
• Unique Identification name for samples under test.
• Test pass/fail indication
• Test duration entry option
• Option for entering thermocouple location or identification name
• Elapsed test duration indication.
• Reduction of current automatically at the end of test duration
• Graphical as well digital display off all the selected channels

Making and Breaking and Endurance Test

• Measuring three-phase voltage and current
• Measuring power factor
• Controlling voltage variac motor of setting the required voltage
• Actuating pneumatic cylinders
• Setting on and off time, and number of cycles.
• Monitoring actual on and off against the set values.
• Storing three-phase voltage, current and power factor against each cycle
• Naming each UUT unique identification name
• Selecting load

NI PXI Saves Time and Money

Using the PXI-8176 platform, we created an extremely reliable, rugged, and highly precise control system to interface with the existing manual test system, thus saving the customer more than $60,000 in obsolescence of the existing hardware. In addition, we moved many of the safety interlocks to the real-time based software, thus reducing wiring and improving the system reliability. The PXI-based system provided the flexibility in performing various test on the switches and sockets, thus saving a lot of time. Most importantly, all the data available were now fool proof and helped our customer achieve UL certification for their products.

For more information, contact:

Mondeep Duarah

Senior Manager – Design and Development

Captronic Systems Pvt. Ltd.

# 19, Alif Arcade 7th Main Road

I Block Koramangala

Bangalore-560034 Karnataka

Tel: +91-80-2 553 5046

Fax: +91-80-2 550 4054

E-mail: mondeep@captronicsystems.com

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