Thermocouples are widely used in automotive industry for temperature testing at product design and EOL (End of Line) stages and for permanent monitoring afterwards. However, with the increasing voltage levels in Emobility thermocouples posses many risks in product design and testing stages. Some of them are safety related risk and have potential to be life threatening for employees (research and test engineers).
Researchers and testing experts in Emobility have seen the following major challenges with using Thermocouples for temperature testing in high voltage applications.
1. Safety: Thermocouples are subject to creating a short circuit and electrocution risks to the employees.
2. Noise: With the Emobility going towards 1000V and even higher 2500V (for commercial vehicles), thermocouples are highly susceptible to noise.
3. Linearity: Though the thermocouples are calibrated for a certain range, they still need complex compensation algorithm to maintain linearity over the range
4. Response Time: Thermocouples are not fast enough and accurate for thermal profiling of key components of Electric Vehicles such as Charging Points, Battery, Motor Windings and Power Electronics.
5. Repeatability: Thermocouples are made of two dissimilar metallic wires and susceptive to material purity which varies from batch to batch and manufacturer to manufacturer.
Solution: Rugged Fiber Optic Temperature Sensors
With the currently available technologies Fiber Optic Temperature sensors stand out clearly to be the most suitable sensors for Emobility applications at higher voltages (250V+). The major benefits of Fiber optic Temperature sensors are:
1. Safety: Fiber optics are safe – highest dielectric strength, ~1pC, tested up to 1500kV
2. Noise: Sensor are immune to electric, chemical and magnetic environments. Being used without any isolation, in applications that has 1500kV+ voltage, up to 25 Tesla magnetic field and chemical environment ranging from 0 to 14pH without any interference to the sensory readings.
3. Size: Ultra small sensors (Diameter of up to 0.4mm) to fit into tiniest spaces.
4. Linearity: Fiber optic sensors transmit light signals through glass, the purest form of silica. The sensors are linear and does not need any compensation and special algorithms.
5. Response Time: Fiber optic temperature system has a milliseconds response level. Response rate varies between 1ms to 200ms depending on the type of monitor selected for the application.
6. Repeatability: Fiber Optic temperature sensors are very stable and repeatable over the entire range without getting influenced by and external fields.
Thermocouples are generally being avoided in Emobility to keep the highest standards of safety at workplace, provide easy tools to engineers for testing and measurement and reduce time in making complex temperature compensation algorithms. Fiber Optic Temperature sensors are being accepted by engineers as the best and even better alternate of thermocouples for Emobility applications.