The Challenge:

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

The Solution:

The automated test control system for switches and sockets was developed on PXI-RT and FieldPoint RT. The system made use of NI 8176 Controller, PXI-6527, PXI-6052E, and SCXI-1102B for endurance tests. FieldPoint system was used for controlling and monitoring ovens for resistance to ageing tests. FieldPoint was also used for monitoring and controlling current for temperature rise tester along with measurement of rise in temperature. Different tests setting are configured in a host PC. These configurations are downloaded to PXI-RT and FieldPoint-RT system, which runs and controls the test system. The user interface is provided on a Host PC.

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. The PXI-RT and Field Point-RT based test system introduced reliability and drastically reduced the human intervention during testing as all the interlocks were taken care and necessary action/s are initiated automatically if any anomaly was detected. Test data is recorded and report is generated from the logged data.

A General description of Tests performed on Switches and Sockets:

Endurance Tests:

In the endurance test first the system moves a variac to set the voltage at which the test is performed, the voltage is different for different switch ratings.The switches are then turned ON and OFF through an arm actuated by pneumatic cylinders. The ON and OFF time are user programmable. During the ON time three phase voltages and currents are acquired and the power factor is calculated. The number of cycles the test runs for is also user settable and is monitored. . There are three sets of loads available they are 32/40A, 6/12/20A and Incandescent lamp load. User has the option to choose any of the loads at a time. The test control system detects is real time if the load is improperly set and generates an alarm. PXI-RT along with PXI-6527 and SCXI-1102B were used to realize the endurance test system.

Resistance to Heat and Resistance to Aging:

Resistance to Heat tests performed by keeping the switches and sockets samples in an oven. The samples chosen from a batch of production are introduced into the oven for user specified duration and the oven temperature is kept at a user specified value. The temperature of the oven is continuously monitored and logged. Closed loop controlling of temperature of the oven is done through FieldPoint. Resistance to aging is performed on another oven where samples are kept for a longer duration.

Temperature Rise Tester:

Temperature rise tester is used to measure the rise in temperature around the socket pins with respect to the ambient temperature. In this tester three sockets or switches are mounted and they are connected in series. This tester carries an autotransformer whose output is connected to the sockets or switches in series. Thermocouples are placed 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. This test is performed at a constant current by controlling the autotransformer with a motor through FieldPoint in closed loop. The current with respect to time is also monitored and logged.

System Configurations:

The PXI-RT and FieldPoint-RT based Automated Test System for switches and sockets is designed to cater to five Endurance test stations, two Temperature rise testers and two ovens. All these nine systems can run simultaneously or in any combination independent of each other without interfering with the functionality of the other. Data logging is performed on the PXI controller. Data acquired by FieldPoint is also stored in the PXI. In case link to the PXI is lost temporarily because of some unforeseen issue FieldPoint data is logged to its non-volatile flash memory. Later when connection is established data is automatically transferred to the PXI through FTP.

The five endurance test panels are controlled by PXI-RT controller. Labview RT program running on the PXI calculates the power factor by capturing the voltage and current signal only when the switches are ON. Since 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 like staying continuously ON or pneumatic air pressure fails or continuous open circuit condition of the switch occurs the system shuts down with a visual and sound alarm actuated by the PXI-6527. System also generates an alarm if the load setting is not as per requirement. These alarms are also stored. Other interlocks like current and power factor crossing limits are also handled.

Two ovens are used for performing resistance to heat and resistance to ageing tests. FP-2000 controls the heaters in a closed loop. It also monitors the oven temperature. In case oven temperature shoots up above the shutdown limit the heater is turned off 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 of with message.

FP-2000 is also to control two temperature rise testers. Here, switches or sockets are mounted on a fixture and a constant current is passed through them. This constant current is controlled by a motorized variac. Rise in temperature is monitored by FieldPoint RT software. Software also monitors if there is any fluctuation in current because of failure of the switch. It also checks it the temperature rise and current crosses limit. If any of these cases occurs the system is turned of 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 happens simultaneously for all the 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 user can start the test. The configuration is transmitted to the PXI-RT and FieldPoint-RT system through TCP/IP. The host system provides a display screen for monitoring the test. During the test the host will be getting continuous feed back from the PXI-RT 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.
• Monitoring and logging of oven temperature and ambient temperature with timestamp.
• Unique Identification for units under test by giving a name to each test.
• Test duration monitoring-Display of elapsed time for a particular unit under test.
• 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 shaft of autotransformer.
• Monitoring & 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.

Temperature Rise Test:

• Controlling of current delivered by the autotransformer by controlling a motor attached to the shaft of autotransformer.
• Monitoring & 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.

Conclusion:

With the PXI-RT platform we were able to put up an extremely reliable, rugged and highly precise control system to interface with the existing manual test system thus saving the customer over US$60,000 in obsolescence of the existing hardware. In addition many of the safety interlocks were moved to the RT based software thus reducing wiring and improving the reliability of the system. PXI based system provided the flexibility in performing various test on the switches and sockets saving a lot of time. Most importantly all the data available were now fool proof and enabled our customer to get UL certification for their products by the automation of testing and its report generation.