Minimum impedance for o-scope auto use?

My Bentley service manual cautions to use a meter (seems to be inferring DMM) of at least 10 megaohms input impedance to prevent excessive current draw that possibly might damage "sensitive electronic components."

I'm looking to buy an older 2-chan scope, and am finding most are rated a 1 megaohm.

Is the Bentley caveat referring mostly to ECUs? Among a long list of items, I would like to measure a load freq output of the ECU, along w/such things as fuel injector PW, knock sensor VAC output, primary and secondary ignition (using a capacitive pickup and correct attenuation probes), O2 sensor, alt AC ripple, Hall-Effect sensor, Air Mass Meter, fuel pump - basically as much as I can

Car is a 91 Saab 900: one fuel and one ignition computer (2 total), hot-wire air mass meter, solenoid injectors, one coil, distrib cap and rotor

I've seen leads that change pf. What components shouldn't I use a 1 megaohm scope on (trying to determine how useful/restrictive scope use would be)?

Thank you Lance

Reply to
Lance Morgan
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On 2 Aug 2003 09:08:00 -0700, snipped-for-privacy@yahoo.com (Lance Morgan) wroth:

When you get your scope, (old or new, they're ALL 1 Meg input), make sure you get a couple of 10:1 attenuator probes too. The probes make connections easy and they have a 10 Meg input impedance with minimal capacitive loading.

Using the probes, you can measure anything from 10's of milivolts up to

500 or so volts. The only place you shouldn't put them is directly on the secondary of the ignition coil output.

Jim

Reply to
James Meyer

X-No-Archive: Yes

You'll want to get a 1:10 probe anyways. Without it, most scope can only do five volts per div, maxing out at 20V or so peak in either direction.

Lance Morgan wrote:

Reply to
AC/DCdude17

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