Surviving Vibration at 200MPH: Harsh Environments for Sensors in Racing
By Lynnette Reese, Mouser Electronics
Sensors and signals have become vital to success in racing. Sensors assist in monitoring, controlling, and optimizing both car and driver by taking in copious data about braking, cornering speeds, throttling, gearing, wheel spin, duration of shifting, and the range of speeds where the engine operates most efficiently. The data is used to analyze the performance of the engine, suspension, exhaust system, and steering, so that racing team engineers can design to win. But one of the greatest barriers to success is the harsh environment that racing delivers, in terms of excessive temperatures and vibration that destroys the accuracy of sensors and eventually the device itself.
When a sensor travels at 200MPH
The same devices that were originally designed for heavy duty applications in hydraulics, boilers, jet engines, and in the military share the same properties that make them robust, with excellent protection against moisture, very fast response times, resistance to vibration, and the ability to continue operating accurately at high temperatures over years or millions of cycles. Racing includes extreme conditions.
Mouser Electronics sponsors KV Racing. Josh Fults and Matt Cummings, Data Acquisition Engineers for KV Racing, solve problems and find solutions for gathering performance data both on and off the race track. The team races more than half of the weekends in a year, and at many different venues. When the car is going 200MPH, minor issues with each new track create new challenges, such as new patterns of vibration. Electronic components need to perform with excellence, designed with a low total error that addresses issues such as the reduction of drift. Drift is the tendency for a sensor to lose accuracy over time, and less than ten degrees of error can provoke permanent component damage and catastrophic engine failure. With a hundred or more sensors on a typical racing car, the total burden for precision in data acquisition can be enormous.
Figure 1: Tony Kannan in the driver's seat as engineers inspect the Mouser-sponsored KV Racing Technology No. 11 car.
What causes error like “drift”?
Over time, vibration can destroy a sensor or cause it to be less accurate. Drift occurs when harsh conditions cause a sensor to lose accuracy over time. Racing teams use sensor data to evaluate performance after making changes, to troubleshoot issues, and to analyze trends. Harsh environments break down materials, introduce noise into the system, and cause overall havoc if components are not designed with high temperatures and excessive vibration in mind. The harsh racing environment also introduces dust, oil, and moisture into the mix. The solution to this challenge boils down to materials science.
Conventional protection from vibration is focused on mounting hardware. Reliability is compromised over time if electronic components are not protected from vibration or are not inherently designed with resistance to critical fatigue of materials. Vibration can create noise in an electrical signal, and most noise occurs at the atomic level. Mechanical vibration is translated to the signal chain via mechanical strain, intermittent contact, or varying electromagnetic field strength. Loose parts, particles, or faulty bond wires or cables, and enclosure covers may all contribute to mechanically-induced noise. Error is introduced as elements are exposed to the harsh environment. Materials break down, then they no longer perform as expected, and this is how drift is introduced. “Drift” is why data acquisition engineers are tasked with re-calibrating and testing sensors before every race. Over time, drift gets more pronounced and devices have to be replaced when calibration doesn’t hold sufficiently or long enough to finish a race.
How can drift be reduced or avoided in harsh conditions?
Sensors that are designed for high-vibration harsh environments can maintain accuracy with careful structural design, including a stiff and light structure; heavy enclosures are not enough. To avoid the effects of vibration, damping is maximized, and sensors are well-sealed to avoid direct acoustic excitation, as well as moisture, dust, and oil. An additional effort can be made to actually tune vibration absorbers that reduce vibration at expected frequencies. Advanced methods include active electrical cancellation of noise using an accelerometer to measure vibration and produce a voltage, which is amplified and fed back to oscillator frequency tuning control.¹ Additionally, the use of digital electronics has contributed tremendously to accuracy in harsh environments, since most natural noise is analog and much easier to prevent or remove from a string of discrete digital bits. A common sense rule-of-thumb for avoiding mechanically-induced noise is to stabilize coil windings, coaxial cables, jumper wires, and the like; as well as not to rely on enclosures alone, because enclosures are poor vibration isolators.
What does an Indy series race team monitor in harsh conditions?
Information that is either displayed real time or recorded for post-race analysis is engine load or manifold absolute pressure (aka “boost”), RPMs, throttle position, air and water temperatures, fuel level, tire pressure, the percentage of oxygen in the exhaust (a measure of fuel/air mixture), roll bar position, and detailed information such as 3-axis acceleration, mechanical displacement, and rotational speed.
The following is a discussion of a few sensors that are used for gathering data: Engine, tire, brake, exhaust, and fluid temperatures; tire pressure, steering, axle, and suspension movement; throttle angle, and acceleration and g-forces in specific areas.
Measuring temperature from a distance: Tires, Brakes, Exhaust, and Engine
Contactless temperature sensing is most often invested in the brakes, engine, and tires. Temperatures for these areas are measured on the racetrack, and can be wirelessly transmitted back to the crew in real time for data analysis. Infrared sensing inside, in the center, and on the outside of a tire measures temperatures remotely. The TMP006 from Texas Instruments is the world's first single-chip, digital infrared (IR) temperature sensor. It works when an on-chip thermopile absorbs the infrared energy emitted from an object, and uses the corresponding change in thermopile voltage to determine temperature. At a small 1.6mm x 1.6mm, the TMP006 operates at extreme temperatures and requires very little power to operate, making it ideal for data logging on a race car where size and weight are important. The TMP006 measures the temperature of an object within an adjustable field of view (up to 150 degrees) and the ambient temperature, without the need to make contact with the object.
Figure 2: Principle of operation, the contactless TMP006.
Exhaust temperatures are used to measure immediate response to fuel mixture changes. Exhaust re-circulation temperatures can be measured directly with the Honeywell ES110-0017, an air/gas sensor with an exposed thermistor element that offers enhanced response for greater levels of engine fuel mixture control, and are intended for this purpose.
Steering, Axle, and Suspension
To determine if a steering wheel is the cause of a handling problem and not the driver, Hall Effect sensors are used. With frictionless measurement in movement for steering, axle, suspension, or drive shaft, they measure without physical contact. Bourns AMM20B multi-turn magnetic position sensor is a Hall Effect sensor specifically designed for steering and suspension. They have a rotational life of 30 to 50 million cycles, operate in temperatures up to 125°C, and are highly resistant to vibration, and fluid or dust. Steering information enables better communication between the crew and driver. The steering angle is correlated to an analog output voltage with a programmable slope for customization.
Figure 2: Bourns' high life cycle magnetic position sensor.
Sensing Hydraulic, Brake, Oil, and Coolant Pressure
The most common automotive applications require 100, 250, or 1000 PSI, the latter for brakes. Pressure data is also gathered from the engine manifold for analysis on engine performance. Honeywell's 5000 Series extended heavy duty pressure switches are intended for automotive use and operate from 91 psi to 150 psi. Trip points for these pressure switches are field-adjustable factory set points from 0.5 to 150 PSI.
The “G” Force Sensor, or Accelerometer
Accelerometers are available that sense along one, two, or three directions. In racing, a single axis can be used to measure lateral G-force, also called “cornering,” or it can be used to sense longitudinal forces such as braking in a range from 0 – 4G. The position of the sensor determines what direction gets sensed, for a single axis unit. A dual axis sensor measures both forces for cornering and braking in a single device. The ST Microelectronics LIS3DSHTR measures ±2g/±4g/±6g/±8g/±16g on a dynamically selectable full scale and can be configured to generate interrupt signals activated by user-defined motion patterns. The 14-bit LIS3DSHTR is designed to survive a 10000 g high shock, operates from -40°C to 85°C, is state-programmable, and consumes a minuscule amount of power at 11μA in active mode.
Design to Win
Harsh conditions pose a challenge, but products exist that are designed for harsh long-term environments. All of these sensors have something in common: they are designed to withstand high temperatures and vibration, and they are all available at Mouser Electronics, with the newest sensors for the latest improvements in racing data acquisition. Design to win with Mouser Electronics.
¹ Vibration-Induced Phase Noise in Signal EFTF IFCS 2009 Joint Generation Hardware – Conference
Besancon, France April 20, 2009 Joseph B. Donovan and Michael M. Driscoll
Lynnette Reese is a member of the technical staff at Mouser and holds a B.S. in Electrical Engineering from Louisiana State University. Prior to Mouser, she completed a combined 15 years in technical marketing in embedded hardware and software with Texas Instruments, Freescale, and Cypress Semiconductor. She started her career as an applications engineer at Johnson Controls.