Scoping a Signal Without Influencing it

[Hijawi]

Hello All!

I am trying to scope a crankshaft position signal, while keeping the sensor connected to the vehicle's ECU, I am using MyRio's MSP connector C analog inputs as they have higher impedance, but still when I try to scope the signal on the differential input +0/-0 the crank signal seems to be disturbed and the ECU will fail to time the ignition and injection. I was thinking to have a positive unity gain amplifier with high resistor values. As I was reading the manual for MyRio, my signal seems to be the floating signal.

Your help is much appreciated.

[DiegoH214]

Hello Hijawi,

As I understand, you have the ECU, the Sensor and the myRIO terminals connected together. The signal of the sensor acquires correctly on the myRIO but seems disturbed and the signal does not arrives to the ECU? Are you using any pull up or down resistors? Do you have a oscilloscope to see the signal?

Diego H

National Instruments

[Hijawi]

Hello John,

I scoped the signal with the oscilloscope and myRIO successfully, however when the sensor terminals are connected to scoping device, the signal reaches the ECU a bit disturbed, the engine takes a long cranking and not starting and doesn't run for long, I am not using any resistors because the signal is already small, I want to know the right way to increase the impedance of myRIO in hopes of minimizing the losses while scoping the signal.

Your help is much appreciated,

Hijawi