Application of Fluke Multimeter in Automobile Maintenance
Duty cycle (on-off ratio)
Duty cycle is a measurement of pulse width modulation circuits. For example activated carbon canister cleaning coil. For example, the larger the duty cycle, the longer the circuit is on, the higher the flow rate, or the more the probe tank is cleaned. 100% duty cycle means the solenoid is always on. A 10% duty cycle means fueling only a fraction of the time. The ECU decides when and at what flow rate the probe can be cleaned. These adjustments are based on engine temperature, how long the engine has been on, vehicle speed, and a few other dynamic parameters.
Test the duty cycle of charcoal Canister
Test the duty cycle of the solenoid valve. The red pen is connected to the signal terminal, the black pen is reliably connected to the engine ground, and the measured value can be directly read out by selecting the duty cycle test on the multimeter.
Cooling system/temperature measurement
With today's computer-controlled engines, the right temperature is critical. The temperature measurement function built into the Fluke 78/88 makes it easy to check the engine's cooling system. The cooling system, heating (hot air) system and air conditioning system can also be checked using the F78/88 table.
With pin thermocouple temperature probes, thermostats and fan switches can be tested without having to heat up the tank on a hot day. For other types of electrically controlled cooling systems, diagnostic information can be obtained quickly and accurately and can be compared with the actual information calculated by the computer.
On many of the latest cars, the cooling system is hermetically sealed. The only opening is the EXPANSION TANK. Because it has no water circulation, it cannot accurately test the temperature. The only way to accurately test it is to measure the radiator inlet side of the radiator box.
Test the temperature switch
When checking the operation of the cooling fan, connect the temperature probe directly to the switch of the water tank. Note the temperature numbers when the fan is on and when the fan is off and compare to the manufacturer's specifications.
Test Switch Continuity
Use the resistance range of the multimeter to check the continuity of the temperature switch. Test the voltage drop across the switch and from the heat sink to ground. Note that the temperature when the fan is off should be higher than when the fan is on.
