Scope Measurement Hints

Probing Sanity Check

Before probing a circuit, connect your probe tip and your ground lead to the same point on your circuit (usually ground) to check for com-mon mode rejection. Ideally you should get a flat line on your scope. If you get blips (common mode noise), this inaccuracy will be reflected in your measurements. You may need to make adjustments to your probing to make a better measurement.

For instance, in the following example, shortening the ground lead did the trick.

In Figure 1 the circuit ground is probed with a 5" ground lead. In Figure 2, the same signal ground is probed with a 1/2" ground lead. The blips are no longer big enough to have much affect on your measurement.