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Car Inductive RPM Sensor simulation

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rezaf

New Member
Hi, I'm building a test bench for testing some automotive parts but need to simulate the output signal of RPM/Crankshaft Sensor for ECU to avoid including the real flywheel in the test bench.
the own sensor has 3 wire and I think it's inductive type because : I seen 800 ohm Resistance between two pin and when I connect oscilloscope probe to this two pin, I see sine wave on the oscilloscope. although in the car, when I unplug one of this two pins the engine will turn off and also if I unplug this pins, the car will not turn on. the frequency of output signal of this sensor changes according to the throttle change, for example when I push throttle pedal to 1000, the frequency reach to about 1KHz.
Can I simulate this signal for the car ECU with a function generator or create special circuit without using the sensor?
 

MikeMl

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Does this shed any light on it?
 

JimB

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Title edited from PRM to RPM.

JimB
 

MikeMl

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It would be helpful if you could identify the three wires that go into the module.

Is one connected to +5V from inside the ECU?
Is one grounded, maybe at the the ECU?
Is one (likely the output) just go to a pin on the ECU? If so, can you probe it with a 'scope? Show us the waveform?
 
I'm a little confused. Is this a 3 wire Hall effect sensor or a 2 wire inductive sensor? They are two totally different animals and create two totally different types of wave. Hall effect will be a digital signal and the 2 wire will be analog. Which one do you have or which one do you need? What are you trying to simulate? If this is for the instrument cluster it can be done with a signal generator. What type of car are you using?
 

debe

Active Member
My mazda has a crank shaft sensor that is inductive with 3 wires but only 2 are used. This is the output of it. Has a resistance of 550 ohms MAZDA 323 CRANK SENSOR.JPG
 

debe

Active Member
This is my tester made out of an old VCR Capstan motor with Toyota parts. I can vary the speed of the motor.TOYOTA RELUCTOR CRO.JPG TOYOTA.1.JPG TOYOTA.2.JPG
 
Still confused. First signal does not look like an analog signal at all. It turns on, dissipates, turns off and then right back on again. You can see the second one is analog as it follows the exact curvature of the vanes and is opposite to the first one. It ramps up voltage and then suddenly shuts off. That makes sense to me. I will have to look into this because I have not seen a three wire inductive sensor used in automotive. Or if I have, never paid enough attention to them. Always looking for an education. New topic to research :) Thanks Debe.
 

debe

Active Member
The Mazda sensor is definitely an Inductive sensor. There is 3 wires only 2 show a resistance, The 3rd black wire may go to a shielded braid as theres no conection to the sensor.MAZDA CRANK SENSOR.JPG
 

alec_t

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The 3rd black wire may go to a shielded braid as theres no conection to the sensor.
That's what Wikipedia says.
 
That would still make it a two wire sensor but what do I know. On the other hand, if this is a Hall effect sensor as you say, where does the resistance come from? I know an inductive sensor is a wire wrapped around a permanent magnet and will have resistance on it, but not sure where resistance comes from in a Hall effect. As well, a Hall effect sensor has to have power, ground and signal so how do these two wires pull that off? I have a Picoscope and generally, all 3 wire sensors that are digital, emit a nice square wave pattern. I don' t see that in your pattern?
 

alec_t

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You are correct. My apologies.
Going back to answer the question. Yes you can simulate this signal with a function generator.
 
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rezaf

New Member
thanks friends. there is no +5v on this 3 wire. I guess one wire is shield too. if I can simulate the signal with function generator, how can I simulate flatten teeth of reluctor wheel?
 
Not sure what you are asking. Even with flat teeth you should get a nice sine wave. I run my test bench with function generator and run instrument clusters all the time this way. Some have to go through ECM on to the CAN bus and still work properly. I don't think flat teeth will affect your signal.
 

alec_t

Well-Known Member
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how can I simulate flatten teeth of reluctor wheel?
Is this the same as simulating 'missing teeth', to identify the shaft zero angle reference point? I guess whether or not you need to do that depends on your particular ECM and on the actual tests you want to do. It's certainly doable.
 
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