Using an Oscilloscope correctly???

[RSW]

Hi There,
It's just a quick post.
I have some running problems with my car and I need to look at the BG and DG sensors.
FOr this I will be using an Oscilloscope. I just wondered if anyone could give me a brief idea as to how to set it up.

I haven't used one since school and I'm just a little rusty.

Any thoughts?

Thanks
RIchard

[jyl]

1. Connect oscilloscope to line-out of stereo system.
2. Start playing Pink Floyd "Dark Side of The Moon".
3. Ingest considerable quantity of [deleted].
4. Study waveforms.

Anyway, that's how I remember using an oscilloscope in school . . .

Sorry, not very helpful.

[RSW]

Ha Ha, I wish I'd paid more attention. I never thought I'd see another oscilliscope in my life - and hear I am.

Richard

[Early_S_Man]

Richard,

I assume you are intent on viewing the signals from the reference and timing sensors going to the DME ...

An extension for the two connectors will be need to be fabricated, I believe, as there really isn't a good point to connect the scope probes to. After the four test points are available, you want to make sure that you don't connect the scope probe 'ground' clip reversed for the second channel ... shorting out the second channel signal! My suggestion would be to disconnect the ground clip on the second probe ... it shouldn't cause any problem, because those are relatively low frequency signals. The chassis common will provide a ground reference for the second channel, unless it is a very special scope using completely isolated inputs, such as the Tektronix 222PS model, which was designed for use with high-Voltage industrial power circuits.

Just as a matter of curiosity, what brand and model scope are you using?

[Superman]

I knew that if Warren saw this thread, he'd provide perfect advice.

[RSW]

The make & model are Tektronix TDS 220, I had a look at the unit last night although I didn't do any work on the car.

Just to clarify, if I understand correctly I am running the two channels at once, but only grounding the first channel by hooking it to the cars earth somewhere?
Can I just unplug the connections at the harness point and take a reading from there or do I have to have the wires connected to the DMS as normal?
- I guess I should have read my Bentley manual last night regarding this topic...

Thanks
Richard

[Early_S_Man]

Richard,

The instructions I gave with respect to the grounding of probes would only be valid for sensors connected to the DME unit, depending on connection to a common ground through the brown wires of the sensors.

For testing during cranking with the sensors disconnected from the DME unit, you would need to connect the oscilloscope probe grounds to the brown wires and the probe tips to the white wires of each sensor.

Bentley doesn't give any tests with an oscilloscope for the sensors. Did you do the Ohmmeter check with a digital multimeter ... 960 Ohms +/- 10 %?

[RSW]

I did do this test and I did get a correct reading from the sensors.
I was tinkering with the car last night and I am now not so sure it's these sensors.

Richard