The reliability of variable reluctance (VR) speed sensors is critical. These sensors must be able to operate in the hardest conditions and be highly compatible with all parts of the system. They need to be resistant to external factors such as temperature, humidity, dirt, and some chemicals. Additionally, the sensors must give reliable information without the results being affected by electromagnetic fields and the vicinity of other sensors.
For this project, we needed to design a complete test system for all the different electrical and mechanical aspects, ranging from the creation of the feeler gauge to the programming of the software that verifies the different speed sensors.
The system carries out the following two main tests on the VR sensor:
1. Measurement of the nominal resistance and inductance of the coil, including checking that the values for the resistance and the inductance of the sensor’s coil are within normal working parameters.
2. Measurement of the induced voltage. We can use the NI PXI-6515 module to control the servomotor of a cogwheel that simulates a tyre of rotation. The rotation excites the sensor’s coil to generate a voltage signal. We can use the NI PXI-4072 digital multimeter (DMM) and the NI LabVIEW Advanced Signal Processing Toolkit to measure and analyse the signal to obtain its shape, amplitude, and phase angle. We can also use a signal from the servomotor to transmit the data from the DMM and to measure the induced voltage, always on the same wheel cogs. We used this measurement method for each VR sensor, otherwise we would have different voltage measurement for each pin and the potential cost of the R&R analysis would increase by 100 percent.
One of the benefits of using the NI PXI-4072 DMM together with the NI PXI-2503 digital I/O module was that we could carry out multiple measurements such as resistance, inductance, and voltage using a single instrument. This provided significant cost savings. Also, using the NI PXI-6515 digital I/O card meant we could directly control the servomotor and the feeling gauge’s rotation without the need for additional hardware, which resulted in additional savings over using a programmable logic controller just for this task. Finally, implementing the tester in the PXI industrial platform led to a small and modular system. Therefore, we could fit all the testing equipment for the digital signals, analogue measurements, and commutation, as well as the equipment for processing and mathematical analysis, in a small rack, which reduced the size of the testing cabinet.
We developed the application using LabVIEW software and designed the user interface to visually portray the resistance, inductance, and signal phase values. Additionally, a large indicator shows if the part meets the pass/fail requirements so the operator can discard the faulty sensors (Figure 1).
We designed the application logic to take advantage of the graphical nature of LabVIEW by using a state machine-based architecture. This helped us build the application for one single environment, one sensor at a time, and in a short time. Also, when we needed to double the number of systems to test the sensors in parallel (Figure 2), making the necessary modifications to the code was simple because we could reuse most of the original code and just needed a bigger rack to fit the additional instruments.
Advantages of Using the NI Platform
We designed and developed, from beginning to end, a test system that meets our immediate testing needs and has the capability to grow for future applications using NI software and hardware, as well as the assistance of the NI Mexico sales and support team. We completed the project in just six months and our costs were reduced, saving us approximately $800,000 USD in one year. We are working on more projects using the NI platform because of the flexibility and scalability of the products, as well as the quality of the company’s service and support.
Ing. Alejandro Sarabia
Cd. Juarez, Chih.
Tel: (656) 649-8646