What is a Tire Pressure Monitoring Sensor (TPMS)?

A Tire Pressure Monitoring Sensor (TPMS) is an electronic system designed to monitor the air pressure inside the pneumatic tires on vehicles. It reports real-time tire pressure information to the driver using a gauge, pictogram display, or a simple low-pressure warning light. TPMS can be divided into two types: direct (dTPMS) and indirect (iTPMS).

Direct TPMS (dTPMS)

Direct TPMS (dTPMS) directly measures tire pressure using hardware sensors. In each wheel, most often on the inside of the valve, there is a battery-driven pressure sensor which transfers pressure information to a central control unit that reports it to the vehicle’s onboard computer. Some units also measure and alert temperatures of the tire as well. These systems can identify under-inflation for each individual tire. Many TPMS products (both OEM and aftermarket) can display real-time, individual tire pressures whether the vehicle is moving or parked.

A direct TPMS sensor consists of the following main functions requiring only a few external components — e.g. battery, housing, PCB — to get the sensor module that is mounted to the valve stem inside the tire:

  1. Pressure sensor
  2. Analog-digital converter
  3. Microcontroller
  4. System controller
  5. Oscillator
  6. Radio frequency transmitter
  7. Low frequency receiver
  8. Voltage regulator (battery management)

The pressure sensor measures the air pressure inside the tire and converts it into an electrical signal. The analog-digital converter then transforms this analog signal into a digital format that can be processed by the microcontroller. The microcontroller handles the overall control and processing of the sensor data, including transmitting the pressure information via the radio frequency transmitter.

The system controller manages the overall operation of the TPMS sensor, coordinating the various components. The oscillator provides the necessary clock signal for the digital circuitry. The low frequency receiver allows the sensor to receive commands or programming data from the vehicle’s central control unit.

Finally, the voltage regulator ensures the sensor module is powered with the appropriate voltage, managing the battery life which can range from 5 to 10 years.

Indirect TPMS (iTPMS)

what is a tire pressure monitoring sensor

Indirect TPMS (iTPMS) systems do not use physical pressure sensors; they measure air pressures using software-based systems. These systems evaluate and combine existing sensor signals such as wheel speeds, accelerometers, and driveline data to estimate and monitor the tire pressure without physical sensors.

TPMS Installation and Regulations

TPMS are installed either when the vehicle is manufactured or after the vehicle is put into use. The goal of a TPMS is to avoid traffic accidents, poor fuel economy, and increased tire wear due to under-inflated tires through early recognition of a hazardous state of the tires.

Mandates for TPMS technology in new cars have continued to proliferate in the 21st century in Russia, the EU, Japan, South Korea, and many other Asian countries. From November 2014, TPMS became mandatory for new vehicles in the European Union.

Aftermarket valve cap-based dTPMS systems, which require a smartphone and an app or portable display unit, are also available for bicycles, automobiles, and trailers.

Technical Specifications of Direct TPMS

  • Pressure Range: 0 to 150 psi (0 to 10.3 bar)
  • Temperature Range: -40°F to 257°F (-40°C to 125°C)
  • Battery Life: 5 to 10 years
  • Transmission Frequency: 315 MHz or 433 MHz
  • Transmission Range: Up to 100 feet (30 meters)
  • Operating Voltage: 3.0 to 3.6 volts
  • Response Time: Less than 10 seconds
  • Accuracy: ±2 psi (±0.14 bar) or better

DIY Installation of Direct TPMS

  1. Purchase a TPMS kit that includes sensors, a display unit, and a wireless receiver.
  2. Locate the valve stem on each wheel and remove the existing valve cap.
  3. Install the new TPMS sensor onto the valve stem by screwing it on tightly.
  4. Initialize the sensors by following the manufacturer’s instructions, which may involve programming the sensors to the vehicle’s specifications.
  5. Connect the wireless receiver to the vehicle’s onboard diagnostic (OBD) port or power it using the cigarette lighter adapter.
  6. Mount the display unit in a convenient location in the vehicle, such as on the dashboard or windshield.

By understanding the technical details and installation process of a Tire Pressure Monitoring Sensor, you can ensure your vehicle’s tires are properly inflated, improving safety, fuel efficiency, and tire lifespan. Whether you opt for a direct or indirect TPMS system, regular monitoring and maintenance of your tire pressure is crucial for optimal vehicle performance and safety.

References:
What is a Sensor?
Tire-pressure Monitoring System
The Importance of Tire Pressure Monitoring
When Tire Pressure Monitoring Gets Smart: FAQ