Testing ABS-sensors with Rigol DS1054z - Page 1
Forum section: electronics / beginners

author: fogaz
author_rank: Newbie
timestamp: September 06, 2015, 09:16:18 am
content: Hello,I recently bought Rigol DS1054Z. I have used different types of oscilloscopes at school, but mainly for small electronics and such. Now i have a problem with my car (Ford Mondeo 2003), one of the ABS-sensors is acting up. Ford uses active sensors which means that there is two wires going into the sensor, one is power supply and the other is signal if i have understood everything right.I have tried to test these sensors by connecting my oscilloscopes test lead to the signal wire of the sensor and the ground wire to the vehicles ground. Then ignition to the ON-position, spinning the wheel and pressing AUTO-button on my oscilloscope.Does anyone know what i'm doing incorrectly? Because as a result i only get strange scrambled signal that just looks like noise-signal and does not have any effect on how fast you spin the tire...

author: Shock
author_rank: Super Contributor
timestamp: September 06, 2015, 10:35:26 am
content: Swap sensors over between the wheels, reset error codes with your code scan tool and test the car again. You could also use a multimeter when they are both out to see if anything is shorted on the sensor and they are both seeing voltage and there is no shorts to ground or any other issues, obviously some tests will require you to disconnect the battery.To answer the oscilloscope question if you look in the workshop service manual it will tell you what signal to expect, it's reasonable to assume the car needs to be on rollers or driving for it to work properly unless you know how to make a test loom for it. If there is a wiring issue or problem from the ECU end that may appear as a bad signal.

author: Psi
author_rank: Super Contributor
timestamp: September 06, 2015, 11:18:54 am
content: Usually its something like 40 pulses pre rev from the ABS tone ring.

author: BradC
author_rank: Super Contributor
timestamp: September 06, 2015, 11:24:19 am
content: Quote from: fogaz on September 06, 2015, 09:16:18 amAre you really, really sure? Every ABS sensor I've come across has been an inductive sensor. So 2 wires, one each end of the coil. You'll get a couple of hundred millivolts at best.

author: fogaz
author_rank: Newbie
timestamp: September 06, 2015, 12:30:49 pm
content: Thanks for the answersQuote from: Shock on September 06, 2015, 10:35:26 amI have tested these things, the problem with this car is that it doesn't give out trouble codes, because the problem is so small that it doesn't show up with code readerQuote from: BradC on September 06, 2015, 11:24:19 amI'm not 100% sure, but Mondeo mk3 doesn't have this toothring that the older model uses, this one has the magnets inside the wheel bearing. Thats why i thought it would be active sensor, not sure thought.I know that the signal is AC-voltage, and should fluxuate depending on the speed of the wheel. Should this Rigol oscilloscope pick this signal by just pressing the AUTO-button or should i do something else with it?

author: max_torque
author_rank: Super Contributor
timestamp: September 06, 2015, 12:57:32 pm
content: "Modern" ABS sensors are 7-14mA sensors. They are current loop sensors (for diagnostics & noise immunity reasons)They pass 7mA when the sensor is not infront of a "tooth" and 14mA when it is, and the more advanced sensors vary the duty cycle proportions to indicate rotational direction of the target wheel.To "test" them off the car, or without the ABS electronics connected, you need to apply 12v (or so, should work from about 8v upwards) and use a series resistor to convert the mA signal into a voltage pulse that your scope can read. Something like a 330ohm resistor should do it, which should obviously have 2.3v across it for 7mA and 4.6V for14mA etcIf you are reading the sensors directly on the car, then the series resistors and power supply are already in the ABS module, so you should be able to just connect the scope between (in high impedance input mode, ie 1/10Mohm) to the sensor return wire and chassis gnd (and expect to get a nice square wave on the screen (the voltage level present will tell you what series burden resistor is being used in the ABS module)

author: Psi
author_rank: Super Contributor
timestamp: September 08, 2015, 11:57:33 am
content: Quote from: BradC on September 06, 2015, 11:24:19 amMaybe if you move the wheel with your hand, but at 200kph you get 100V+Input protection for sensing the signal, using a MAX9924–MAX9927 or similar, usually requires a 10k 2010 resistor in each wire for current limiting and high voltage clearance. Then a 500V 1nf cap after that.

author: electrolust
author_rank: Unknown
timestamp: September 15, 2015, 06:23:09 am
content: Quote from: fogaz on September 06, 2015, 12:30:49 pmThen it's a VR sensor.https://en.wikipedia.org/wiki/Variable_reluctance_sensor