Elevated Temperature Test of Aerospace Fuel Control Systems

Author(s):

Chris Woodhams - Argenta
Alim Khanan - Argenta

Introduction

A fuel metering unit (FMU) has several electronic interface devices (EIDs) that control the quantity of fuel delivered to an aircraft engine’s combustion system to ensure optimum performance. Commonly, during FMU testing, the EIDs are only subjected to ambient temperature, however, when the unit is installed on wing, near the plane’s engines, the operating temperature is significantly higher. Ambient temperature test may not identify temperature-dependant faults in the EIDs, which inevitably increases the volume of deployed FMUs being returned to repair facilities. This is a major issue because when an airline detects a fault in situ on the wing, the repair can cost hundreds of thousands of pounds. 

Elevated temperature test adds time and complexity to the process, requiring a technician to place the FMU into an industrial oven whilst acquiring resistance, voltage, and temperature measurements. This extra complexity means that elevated temperature test is often used as a diagnostic tool when a technician suspects a temperature-dependant electrical fault in a returned FMU.

Using the NI Platform to Improve Quality Control

A major supplier of advanced aerospace and defence technologies approached the engineers at Argenta, an NI Alliance Partner, to create a new test system that would allow elevated temperature test to become a standard test procedure for all FMUs.

In the new tester, we used CompactDAQ hardware and LabVIEW software to acquire measurements related to resistance, voltage, and temperature. CompactDAQ provided the core DAQ and control technologies required for the new elevated temperature test rig.

We used CompactDAQ features such as:

• Analogue Input—Acquiring FMU measurements related to the resistance, voltage, and temperature through the harness and thermocouples
• Analogue Output—Delivering an AC voltage supply to power the FMU
• Digital Input—Detecting when the FMU’s harness has been correctly connected to the interface box
• RS232—Communicating with the oven to control and monitor temperature

The test setup is simple. The operator places the FMU inside an oven on the assembly line and connects the relevant harness between the acquisition system and the FMU. We initiate the test by logging into the LabVIEW software, entering the unit details, and pressing START within the main user interface. During testing, the system performs a series of operations and checks that include:

• Updating the temperature set point of the oven through the RS232 communications to ensure that the temperature correlates to a predefined temperature ramp
• Logging alarms relative to changes in analogue inputs and temperature
• Ensuring that the system is shut down safely, if the test time exceeds three hours
• Updating graphs to visualise live test data on the user interface
• Streaming data to a technical data management (TDM) file for post-analysis

LabVIEW was the perfect choice for this application as we could work in an agile manner and easily adjust the code to meet changes to the requirements. Additionally, the CompactDAQ platform not only gave us an easy solution to interface with the test software, but also met all the requirements for accuracy, reliability, and quantity of signals.

Direct Benefit to Our Client

Our new test rig streamlined the elevated temperature test process, so our client could test all FMUs at elevated temperatures before they ship to airlines. As a result, our client boosted quality control, preventing potentially erroneous products being shipped. This simultaneously minimised repair costs and improved our client’s reputation with its customers.

One senior engineer explained that if an airline or an operator detects a fault in situ, on the wing, the cost to fix the problem could be hundreds of thousands of pounds. This rig increases reliability, enhances our client’s reputation with its customers, and provides a service not offered by competitors.

Conclusion

We used the NI platform to develop an intuitive, robust, and accurate test solution that met all the client’s objectives. Some elements of the software required high levels of accuracy to ensure the reliability of the results obtained. This tester can be left unmanned due to the built-in safety systems, so operators can perform other tasks in parallel to system testing. Finally, thanks to the flexibility of LabVIEW, we have been able to quickly modify the system to test several other aerospace technologies with minimal changes to the code.

Author Information:

Chris Woodhams
Argenta
Tel: 07834 972 999
Chris.woodhams@argentaconsult.com