Difference between revisions of "Sensors"
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Standing for Inertial Measurement Unit, it measures orientation, velocity, and acceleration in all three axes, utilizing accelerometers, gyroscopes, and magnetometers. | Standing for Inertial Measurement Unit, it measures orientation, velocity, and acceleration in all three axes, utilizing accelerometers, gyroscopes, and magnetometers. | ||
====GPS Receivers==== | ====GPS Receivers==== | ||
| − | Obtains GPS data. This is usually used for logging the position of the car, so that you can see where the car is going and compare lines through corners. | + | Obtains global positioning system (GPS) data from satellites. This is usually used for logging the position of the car, so that you can see where the car is going and compare lines through corners. Most commercial modules can get an accuracy around +/-3m, which is enough to plot the course of a run but not detailed dynamics. It's best used in conjunction with other sensors. |
===Sensing Movement of a Single Component=== | ===Sensing Movement of a Single Component=== | ||
====Hall Effect Sensors==== | ====Hall Effect Sensors==== | ||
| − | Detect the presence of a magnetic field. These | + | Detect the presence of a magnetic field. These typically output a pulse signal corresponding to the rotation rate. These are most commonly used to detect and measure rotation, for instance gear position or wheel speed. Unlike a VR sensor, they require an external magnetic force, but this allows them to work at lower frequencies. |
====Variable Reluctance Sensors==== | ====Variable Reluctance Sensors==== | ||
| − | Known also as VR sensors, they detect a change in the magnetic field. Unlike hall effect sensors, they do not require an external magnetic field, so many OEMs use them for cam and crank position sensors. | + | Known also as VR sensors, they detect a change in the magnetic field. Unlike hall effect sensors, they do not require an external magnetic field, so many OEMs use them for cam and crank position sensors. However, they don't work well at low frequencies, since they rely on movement and not position. |
====Potentiometers==== | ====Potentiometers==== | ||
Variable resistor ladders that measure movement. The can be used as driver controls (e.g., for adjusting radio volume), or in linear form for measuring shock travel (among other uses). | Variable resistor ladders that measure movement. The can be used as driver controls (e.g., for adjusting radio volume), or in linear form for measuring shock travel (among other uses). | ||
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====Air Temperature Sensors==== | ====Air Temperature Sensors==== | ||
| + | During testing, the team should record the ambient weather conditions (humidity, any rainfall past or present, visibility, etc.). On the vehicle, an air temperature sensor mounted on the intake plenum can be used to adjust the fuel injector flow rate to compensate for temperature driven air density changes. Air at 0 C is 101% as dense as air at 35 C, yielding more oxygen <!--citation needed-->. This compensation is included in almost every engine control software and the ease of implementation leads it to be one of the most common compensations used. Engine exhaust temperature sensors in the exhaust headers can also provide information on the vehicles performance for design evaluation; if two header temperatures differ significantly, that indicates that there is an issue with the spark/fuel flow/air flow/leakage for one of the cylinders. | ||
| + | |||
====Infrared Temperature Sensors==== | ====Infrared Temperature Sensors==== | ||
| + | Essentially very low-resolution thermal imaging cameras that "see" the infrared radiation coming off of hot things. Can be used to sense tire- or brake temperature. | ||
| + | |||
==Signal Types== | ==Signal Types== | ||
===Analog Sensors=== | ===Analog Sensors=== | ||
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3-wire sensors take power and ground and send a output signal, usually a voltage that corresponds linearly to whatever the sensor measures. The wires are almost never interchangeable. Because they have a power input, they do not need a pullup resistor. Some 3-wire sensors, like the CBR600RR coolant temperature sensor, are actually 2-wire sensors with an internal pullup resistor. | 3-wire sensors take power and ground and send a output signal, usually a voltage that corresponds linearly to whatever the sensor measures. The wires are almost never interchangeable. Because they have a power input, they do not need a pullup resistor. Some 3-wire sensors, like the CBR600RR coolant temperature sensor, are actually 2-wire sensors with an internal pullup resistor. | ||
===Digital Sensors=== | ===Digital Sensors=== | ||
| + | ====Switched==== | ||
| + | Simple on/off signal. The sensor has some threshold which causes it to go from open to closed circuit. Used in buttons/toggle switches, as well as a simple controller for things like the brake light. | ||
====Pulsed==== | ====Pulsed==== | ||
Pulsed sensors send a series of digital pulses where the frequency of the pulses represents the measurement value. Commonly seen in shaft speed sensors. | Pulsed sensors send a series of digital pulses where the frequency of the pulses represents the measurement value. Commonly seen in shaft speed sensors. | ||
| − | ====PWM==== | + | ======PWM====== |
| − | PWM sensors vary the width of pulses at a fixed frequency to represent the measurement value. A simple analog filter can allow a PWM sensor to be approximated into an analog signal. | + | PWM sensors vary the width of pulses at a fixed frequency to represent the measurement value. Typically this is done while holding frequency steady, but technically this isn't always required. A simple analog filter can allow a PWM sensor to be approximated into an analog signal. |
====Serial==== | ====Serial==== | ||
Some "smart" sensors transmit their measurement value(s) over a [[Communication Protocols|communication protocol]] such as CAN Bus, I<sup>2</sup>C, or SPI. This allows multiple values to be transmitted without additional wiring. | Some "smart" sensors transmit their measurement value(s) over a [[Communication Protocols|communication protocol]] such as CAN Bus, I<sup>2</sup>C, or SPI. This allows multiple values to be transmitted without additional wiring. | ||
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{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
| − | + | !Sensor name | |
| − | + | !Use | |
| − | + | !Sensor type | |
|- | |- | ||
|Cam position | |Cam position | ||
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|- | |- | ||
|Accelerator pedal position sensor (APPS) | |Accelerator pedal position sensor (APPS) | ||
| − | |Required for ETC | + | |Required for [[Electronic_Throttle_Control|ETC]] |
|Rotary position sensor or potentiometer | |Rotary position sensor or potentiometer | ||
|- | |- | ||
|Throttle position sensor (TPS) | |Throttle position sensor (TPS) | ||
| − | |Required for ETC, | + | |Required for [[Engine_Control#Alpha-n|α-n engine control]], ETC, can be used as compensation parameter for speed-density or MAF control |
|Rotary position sensor or potentiometer | |Rotary position sensor or potentiometer | ||
|- | |- | ||
|Manifold/intake air pressure (MAP/IAP) | |Manifold/intake air pressure (MAP/IAP) | ||
| − | | | + | |Measures intake air pressure before it goes into the engine, typically in the plenum. Required for speed density control, can be used as compensation parameter for α-n control |
|Air pressure sensor<br /> | |Air pressure sensor<br /> | ||
|- | |- | ||
|Manifold/intake air temperature (MAT/IAT) | |Manifold/intake air temperature (MAT/IAT) | ||
| − | | | + | |Measures the temperature of the air before it goes into the engine. Can be used as compensation parameter for all engine control schemes. |
|Air temperature sensor | |Air temperature sensor | ||
|- | |- | ||
|Coolant temperature (CLT) | |Coolant temperature (CLT) | ||
| − | |Verify that the engine isn't about to blow up, | + | | Used as an approximation as engine temperature. Verify that the engine isn't about to blow up, can be used as a compensation parameter for engine control such as during a cold start. An additional temperature sensor can be used in the coolant loop after the radiator to quantify radiator performance. |
|Liquid temperature sensor | |Liquid temperature sensor | ||
| + | |- | ||
| + | | Oil Temperature | ||
| + | | Used with CLT to approximate engine temperature | ||
| + | | Liquid Temperature sensor | ||
|- | |- | ||
|Coolant pressure | |Coolant pressure | ||
|Verify that the cooling system works, diagnosing problems | |Verify that the cooling system works, diagnosing problems | ||
|Liquid pressure sensor | |Liquid pressure sensor | ||
| + | |- | ||
| + | | Oil Pressure | ||
| + | | Used to ensure proper engine lubrication. Low oil pressure should be indicated to driver and vehicle should be stopped. | ||
| + | | Liquid Pressure sensor | ||
|- | |- | ||
|Fuel pressure | |Fuel pressure | ||
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|- | |- | ||
|Wideband O2 | |Wideband O2 | ||
| − | | | + | |Measures oxygen content of exhaust gas. Can be used as a compensation parameter for closed loop engine control. Used to tune the engine's AFR, diagnosing misfires (AFR will appear higher if a misfire is occurring). Narrowband AFR sensors are not typically used and are not recommended. |
|O2 sensor | |O2 sensor | ||
|- | |- | ||
| − | |Gear sensor | + | |Gear position sensor |
| − | |Display what gear the transmission is to the driver | + | |Used to determine gear engine is in. Display what gear the transmission is to the driver. Not stock on all engines: CBR only has a neutral switch. Easy to create by drilling a hole in the engine block near the shift drum. |
| − | | | + | |Various |
|- | |- | ||
|Neutral switch | |Neutral switch | ||
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|- | |- | ||
|Vehicle speed sensor (at transmission output) | |Vehicle speed sensor (at transmission output) | ||
| − | |Verify differential performance, | + | |Verify differential performance, can be used to calculate what gear you're in |
|Hall effect sensor | |Hall effect sensor | ||
|} | |} | ||
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|- | |- | ||
|Motor position | |Motor position | ||
| − | |Determines what angle the motor is at so the inverter can time the AC phases | + | |Determines what angle the motor is at so the inverter can time the AC phases (see [[Motor_Control#Field%20Oriented%20Control%20for%20Synchronous%20Machines|FOC]]) |
|Resolver, encoder, or hall effect sensor | |Resolver, encoder, or hall effect sensor | ||
|- | |- | ||
Latest revision as of 14:47, 14 April 2023
Sensors measure physical properties, and convert their measurements into electrical signals to be captured by the data logger and used for running the vehicle, diagnosing the vehicle, verifying that the vehicle is running properly, and/or helping to tune the vehicle.
Contents
Sensor Types
Sensing location/movement of vehicle
These sensors are used to tell where the vehicle is, and how it is moving. Dataloggers often have some or more of these sensors built in. With these sensors, where they are mounted on the car may change how useful the data is. For instance, you may find that you want to mount them as close to the center of gravity as possible.
Accelerometer
Measures its acceleration in one or more axes. This may or may not be the actual acceleration of the vehicle, depending on how it's mounted.
Gyroscope
Measures its angular velocity (change in an angle over time) on one or more axes. Again, you'll probably want these axes to line up with those of the vehicle.
Magnetometer
Measures the strength and direction of the magnetic field. Useful for measuring the yaw of the vehicle.
IMU
Standing for Inertial Measurement Unit, it measures orientation, velocity, and acceleration in all three axes, utilizing accelerometers, gyroscopes, and magnetometers.
GPS Receivers
Obtains global positioning system (GPS) data from satellites. This is usually used for logging the position of the car, so that you can see where the car is going and compare lines through corners. Most commercial modules can get an accuracy around +/-3m, which is enough to plot the course of a run but not detailed dynamics. It's best used in conjunction with other sensors.
Sensing Movement of a Single Component
Hall Effect Sensors
Detect the presence of a magnetic field. These typically output a pulse signal corresponding to the rotation rate. These are most commonly used to detect and measure rotation, for instance gear position or wheel speed. Unlike a VR sensor, they require an external magnetic force, but this allows them to work at lower frequencies.
Variable Reluctance Sensors
Known also as VR sensors, they detect a change in the magnetic field. Unlike hall effect sensors, they do not require an external magnetic field, so many OEMs use them for cam and crank position sensors. However, they don't work well at low frequencies, since they rely on movement and not position.
Potentiometers
Variable resistor ladders that measure movement. The can be used as driver controls (e.g., for adjusting radio volume), or in linear form for measuring shock travel (among other uses).
Rotary Position Sensors
These act as more accurate rotary potentiometers. Often they are contactless, meaning they last much longer and for many more cycles than potentiometers do. These are useful as pedal position sensors and steering angle sensors.
Knock Sensors
Sensors that detect engine knocking. These will bolt directly to the engine block, and will usually come with the engine.
there are a buncha different kinds of knock sensors - i'll try to get something sketched out here this week -simon
O2 Concentration Sensors
O2 sensors measure how much oxygen is in the exhaust. This allows you to figure out the air-fuel ratio of the engine. Narrowband O2 sensors can only tell you if you are rich, lean, or at the stoichiometric efficiency of the engine, whereas wideband O2 sensors tell you your exact air-fuel ratio with much more accuracy. Narrowband O2 sensors are usually used by the OEMs for troubleshooting catalytic converters, but most racecars use wideband O2 sensors to help tune the engine.
A wideband O2 sensor needs a wideband controller to connect to an ECU. Sometimes this is embedded inside the ECU, other times it has to be purchased separately.
Pressure Sensors
Liquid Pressure Sensors
Air Pressure Sensors
Strain Gauges
Strain Gauges measure the strain on an object—the deformation due to the forces traveling through it. They have a trace that curves back and forth, which elongates or contracts slightly as the object stretches or compresses. This elongation alters the resistance of the strain gauge, which can be measured with a wheatstone bridge and an amplifier.
Temperature Sensors
Liquid Temperature Sensors
At minimum, most engines will have a single coolant temperature sensor to measure the temperature of the water in the cooling circuit. This is reported to the engine control unit and is used to determine when the engine cooling fans should be turned on. Additional liquid temperature sensors include oil temperature sensors to monitor the health and performance of the lubrication system (the oil-coolant heat exchanger on most vehicles should reduce this as a concern) and additional coolant temperature sensors to assess radiator performance.
Air Temperature Sensors
During testing, the team should record the ambient weather conditions (humidity, any rainfall past or present, visibility, etc.). On the vehicle, an air temperature sensor mounted on the intake plenum can be used to adjust the fuel injector flow rate to compensate for temperature driven air density changes. Air at 0 C is 101% as dense as air at 35 C, yielding more oxygen . This compensation is included in almost every engine control software and the ease of implementation leads it to be one of the most common compensations used. Engine exhaust temperature sensors in the exhaust headers can also provide information on the vehicles performance for design evaluation; if two header temperatures differ significantly, that indicates that there is an issue with the spark/fuel flow/air flow/leakage for one of the cylinders.
Infrared Temperature Sensors
Essentially very low-resolution thermal imaging cameras that "see" the infrared radiation coming off of hot things. Can be used to sense tire- or brake temperature.
Signal Types
Analog Sensors
2-Wire
2-Wire sensors act like a rheostat, a variable resistor. Because of this, the two wires are almost always interchangeable. One wire is wired to the device input, with a pullup resistor to 5V (this pullup may be internal to your ECU) and the other wire goes to ground.
3-Wire
3-wire sensors take power and ground and send a output signal, usually a voltage that corresponds linearly to whatever the sensor measures. The wires are almost never interchangeable. Because they have a power input, they do not need a pullup resistor. Some 3-wire sensors, like the CBR600RR coolant temperature sensor, are actually 2-wire sensors with an internal pullup resistor.
Digital Sensors
Switched
Simple on/off signal. The sensor has some threshold which causes it to go from open to closed circuit. Used in buttons/toggle switches, as well as a simple controller for things like the brake light.
Pulsed
Pulsed sensors send a series of digital pulses where the frequency of the pulses represents the measurement value. Commonly seen in shaft speed sensors.
PWM
PWM sensors vary the width of pulses at a fixed frequency to represent the measurement value. Typically this is done while holding frequency steady, but technically this isn't always required. A simple analog filter can allow a PWM sensor to be approximated into an analog signal.
Serial
Some "smart" sensors transmit their measurement value(s) over a communication protocol such as CAN Bus, I2C, or SPI. This allows multiple values to be transmitted without additional wiring.
Some Common Applications
Driver Training
| Sensor name | Use | Sensor type |
| GPS | Visualize and compare driving lines, visual aid for displaying data on an overlay of the course | GPS |
| Throttle position sensor (TPS) | Visualize and compare driver's throttle pedal control | Rotary position sensor or potentiometer |
| Accelerator pedal position sensor (APPS) | Visualize and compare driver's throttle pedal control | Rotary position sensor or potentiometer |
| Brake sensor | Visualize and compare driver's braking | Liquid pressure sensor, rotary position sensor or potentiometer |
| Steering angle sensor | Visualize and compare driver's steering | Rotary position sensor or potentiometer |
Aerodynamics
| Sensor name | Use | Sensor type |
| Air pressure sensor | Validating aero simulations | Air pressure sensor |
| Air speed sensor | Calibrating downforce calculations for headwind | Pitot tube |
| Shock length sensor | Determining downforce at front vs. rear | Linear potentiometer |
Brakes
| Sensor name | Use | Sensor type |
| Brake pressure sensor (front and rear) | Validate braking system design, determine brake bias | Liquid pressure sensor |
| Brake light switch | Turn on brake light when brakes are applied | Liquid pressure switch |
| Brake rotor temperature sensor (front and rear) | Validate brake rotor design | IR temperature sensor |
Chassis
| Sensor name | Use | Sensor type |
| Strain gauges | Validating chassis stiffness | Strain gauge |
Powertrain: Internal Combustion
| Sensor name | Use | Sensor type |
|---|---|---|
| Cam position | Determine ignition/fuel timing | VR sensor |
| Crank position | Determine ignition/fuel timing and determine engine speed (aka RPM) | VR sensor |
| Accelerator pedal position sensor (APPS) | Required for ETC | Rotary position sensor or potentiometer |
| Throttle position sensor (TPS) | Required for α-n engine control, ETC, can be used as compensation parameter for speed-density or MAF control | Rotary position sensor or potentiometer |
| Manifold/intake air pressure (MAP/IAP) | Measures intake air pressure before it goes into the engine, typically in the plenum. Required for speed density control, can be used as compensation parameter for α-n control | Air pressure sensor |
| Manifold/intake air temperature (MAT/IAT) | Measures the temperature of the air before it goes into the engine. Can be used as compensation parameter for all engine control schemes. | Air temperature sensor |
| Coolant temperature (CLT) | Used as an approximation as engine temperature. Verify that the engine isn't about to blow up, can be used as a compensation parameter for engine control such as during a cold start. An additional temperature sensor can be used in the coolant loop after the radiator to quantify radiator performance. | Liquid temperature sensor |
| Oil Temperature | Used with CLT to approximate engine temperature | Liquid Temperature sensor |
| Coolant pressure | Verify that the cooling system works, diagnosing problems | Liquid pressure sensor |
| Oil Pressure | Used to ensure proper engine lubrication. Low oil pressure should be indicated to driver and vehicle should be stopped. | Liquid Pressure sensor |
| Fuel pressure | Verify that the fuel system works, diagnosing problems | Liquid pressure sensor |
| Wideband O2 | Measures oxygen content of exhaust gas. Can be used as a compensation parameter for closed loop engine control. Used to tune the engine's AFR, diagnosing misfires (AFR will appear higher if a misfire is occurring). Narrowband AFR sensors are not typically used and are not recommended. | O2 sensor |
| Gear position sensor | Used to determine gear engine is in. Display what gear the transmission is to the driver. Not stock on all engines: CBR only has a neutral switch. Easy to create by drilling a hole in the engine block near the shift drum. | Various |
| Neutral switch | Tell the driver if they're in neutral or not | Switch |
| Vehicle speed sensor (at transmission output) | Verify differential performance, can be used to calculate what gear you're in | Hall effect sensor |
Powertrain: Electric
| Sensor name | Use | Sensor type |
| Motor position | Determines what angle the motor is at so the inverter can time the AC phases (see FOC) | Resolver, encoder, or hall effect sensor |
| Motor temperature | Make sure motor doesn't overheat | Temperature sensor |
| Coolant temperature (CLT) | Make sure motor and/or motor controller don't overheat | Liquid temperature sensor |
| Coolant pressure | Make sure there's no leak, make sure water pump is operating correctly | Liquid pressure sensor |
Drivetrain
| Sensor name | Use | Sensor type |
| Rear wheel speed sensors | Verify differential/torque vectoring performance, traction control | Hall effect, VR, inductive proximity sensor |
Suspension
| Sensor name | Use | Sensor type |
| Tire pressure | Verify tire performance, suspension tuning | Wireless air pressure sensor |
| Tire temperature | Verify tire performance, suspension tuning (even camber if multiple temperature readings per tire) | Surface or IR temperature sensor |
| Shock length sensor | Suspension tuning | Linear potentiometer |
| Strain gauges | Verify forces on suspension members | Strain gauge |
| IMU | Suspension tuning | IMU |
