Customer Solutions

Development of a Glow Plug Endurance Test System

Author(s):

G. Giridhar, Captronic Systems

Industry:

Automotive

Product:

Compact FieldPoint, Distributed I/O, FieldPoint, LabVIEW

The Challenge:

Developing automated test equipment to perform accelerated endurance tests for glow plugs and speed up the testing cycle.

The Solution:

Building a system that performs endurance testing while calibrating and controlling the voltage of power supplies and recording various parameters of up to seven glow plugs simultaneously using FieldPoint distributed I/O modules and LabVIEW software.

Glow Plug Usage
At low outdoor temperatures and when an engine is cool, fuel in diesel engines insufficiently ignites or does not ignite at all. Glow plugs aid in starting a diesel engine at these low temperatures and ensure a smooth running engine immediately after starting at low speeds. In recent engine models, the glow plugs also continue to glow for up to several seconds after the engine starts to reduce the pollution content in the exhaust. Glow plugs mount in the cylinder head of the diesel engine with the positive connected to the battery and the negative grounded on the engine block.

A glow plug consists of a heating resistor element welded in series with a positive temperature (PTC) resistor. When the voltage is applied, the heating resistor heats up and the glow plug tip glows. This PTC resistor also limits the flow of current, which stabilizes the temperature and current of the glow plug. We needed an application to automate the testing of the endurance, durability, and life of the glow plugs at a lower cost. The application needed to perform various functions, including applying recipes of voltages on the plugs for different time periods, testing in a cyclic manner until the plug fails, and ensuring unattended operation.

The features offered by LabVIEW and FieldPoint made it possible for us to create this glow plug test system and add additional features to our basic requirements. For example, we were able to use the watchdog features of FieldPoint to program the system to shut down automatically in emergency conditions, such as short circuit or high glow plug temperatures. LabVIEW also gave us the flexibility to control the test system processes and acquire data for tests conducted for several thousands of cycles. The system automatically recovers from power shutdown to complete the balance of any incomplete tests. We can also view test data from any computer on the network. Using LabVIEW and FieldPoint, we were able to develop the Glow Plug Endurance Test System (GPETS) to accelerate the endurance process cycle of the plug.

Creating the GPETS
The system hardware for the GPETS consists of a personal computer and several FieldPoint modules, including FP-1001 for networking from a remote location, FP-AO-210 for controlling the voltage, FP-AI-110s for acquiring the current and temperature, FP-RLY-420 for switching on the power supply, and FP-RTD-122 for acquiring the jig-temperature. The individual tests were a collection of similar tasks, thus it was evident that the code should be modular. Each task was written to be a self-contained, generic sub-VI. Through the use of these software modules and the state machine programming of LabVIEW, we were able to develop different tests. We were also able to present data in a clear graphical format using LabVIEW graphical interfaces and control options to create an easy-to-use, understandable interface.

The GPETS has four main sub-VIs: type program execution, voltage calibration, current calibration, and data entry. These execute in a sequence with the application logging the voltage, current temperature, and number of tests completed until the plug fails. The main panel of this application is the type program execution, which we use to view the user-specified data, start the different endurance programs required for testing the glow plugs, and perform online analysis of the process status of the seven glow plug currents, voltages, and temperatures. The sub-VI also controls data logging of the date, time, number of cycles, voltage, current, and temperature with respect to time.

The voltage and current calibration sub-VIs control the voltage and current for the predefined input, which helps us calibrate the power supplies and the acquired output voltage and current. The data entry sub-VI sets the parameters for the endurance test, which includes controlling voltage for the glow plug, forced cooling time of a plug by the air jet, the number of operations, the warning temperature set point, and the amount of power supply required.

We can enable or disable the DC sources according to the need for the test, which can depend, for example, on the number of plugs connected. We then know whether or not a glow plug is working or if it is not being used. Online graphs are also available for voltage versus time, current versus time, and temperature versus time for the seven glow plugs. We can log the data to a database and view the old test data from the type program history. Automatic shut down also occurs in case of PC communication failure.

An Independent Test System
After running many tests, this National Instruments system has proven to be a very useful tool for testing the endurance, durability, and life period of the glow plugs. On the new LabVIEW system, testing of the glow plugs is done automatically for a three to four week period without requiring human intervention thanks to features, such as automatic shutdown in case of emergencies and restarting operation after power failure. Additionally, FieldPoint makes it possible for us to isolate power supply voltages and controls and develop a distributed I/O system that can run such a large loop-in-loop control application. We achieved all of this at one-fifth the cost of a dedicated system.

For more information, contact:

G. Giridhar or Vinod Mathews

Captronic Systems

Bangalore, India

E-Mail: capsys@vsnl.com

giridhar_g_pc_automotive_2002.pdf

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