ISO PAS 12158:2002 pdf download Road vehicles — Braking systems — Temperature measuring methods
Scope
This Publicly Available Specification presents methods for measuring the temperature of braking systems in roadvehicles. lt is applicable to both disc and drum brakes fitted on passenger cars and commercial vehicles, and itsmethods are suitable for either dynamometer tests in the laboratory or vehicle tests on road and track.
2Continuous temperature measuring methods — Dynamometer and vehicle
2.1 General
Two different, common methods may be used for measuring the temperature of brake discs and drums.
The first is the use of embedded thermocouples in the braking surface of the disc and drum (see Figure B.1). Thismethod generates a need to transfer the signal from rotating to stationary parts by means of slip rings or a powersupply (battery) and telemetry. t is used on dynamometers and in vehicles. The signal transfer from rotating tostationary parts is not necessary if the sensors are embedded in the brake linings (see Figures B.2 and B.3).
The second method is the use of rubbing thermocouples (see Figures B.4 to B.7) A rubbing thermocouple consistsof a thermo-junction loaded by a low-rate spring against the braking surface of the brake disc or drum and thereforenot needing slip ring contacts. The load on the sensor may be up to 1 N but the temperature rise due to selfheating should be less than 15 “C at 50 km/h.
A third method, gaining in popularity, uses an infrared emission sensor operating without any contact between therotating parts, and measures drum/disc temperatures without resort to slipping contacts or wearing parts.
2.2 Installation
Depending on the measuring task, thermocouples may be installed in each brake to establish the hottest braketemperature and reveal any temperature differentials.
In order that the temperature indicator (nowadays, typically a digital meter) can be placed in a convenient positioninside the vehicle, special extension or compensating leads should be used for connecting the measuringthermocouple to this meter.
It is also customary to transfer the cold junction to the meter end. However, modern meters/measuring systemsinclude solid-state cold junction compensation for ambient temperatures between 0 °C and 40 °C — adequate forthe vehicle testing required by regulations.
2.3 Calibration
Calibration is effected by adjustment of the circuit resistance (given a constant load), using an external variableresistor. Various proprietary calibrators are available to suit particular thermocouples. These calibrators insert intothe circuit a voltage which is the same as that produced by the measuring junction at a specified temperature.thereby allowing the external resistor to be adiusted to give a corresponding temperature reading on the meter.
A typical, practical temperature-measuring installation in which automatic cold-junction compensation is employedhas a range of 0 °C to 1 000 C. Multi-channel recording/logging equipment may be added to the circuits (beforecalibration) so as to provide a permanent record of the vehicle brake temperatures during subsequent test stages.
3 Other temperature measuring methods
The tables of Annex A summarize a number of different methods that may be used for measuring braketemperatures in order to meet the requirements of the braking regulations mentioned in the introduction.