What type of Multimeter is safe to use on computers?

In "Upgrading and Repairing PC's - 18th edition" by Scott Mueller on pg. 1278 he discusses multimeters. "You should only use a DMM (digital multimeter) instead of the older needle-type multimeters because the older meters work by injecting 9V into the circuit when measuring resistance, which damages most computer circuits.

A DMM uses a much smaller voltage (usually 1.5V) when making resistance measurements, which is safe for electronic equipment."

1. Most DMM's that I've looked at have 9V batteries. Are they internally stepping down the voltage used when making these measurements?

2. Wouldn't the concern of injecting 9V be true when measuring continuity as well?

3. A little off topic, there is a fascinating way to test for laptop screen inverter failure, (http://www.fonerbooks.com/test.htm), is anyone aware of a safe DMM that is capable of this as well?

Solution 1:

I think my fairly generic DMM has a resistance measuring voltage of less than a quarter of a volt and a continuity check voltage of less than one volt. The continuity range also tests diodes, so it has a higher voltage to overcome the voltage drop of a diode. When measuring voltage, it has a resistance of over 30 MOhms.

I think you will be fine with any slightly modern DMM. So long as you are careful where you stick it. :)

Solution 2:

I've used regular DMMs for years, they're perfectly safe so long as you don't get the very cheapest or really old ones - stop worrying :)

Solution 3:

While true, this may be somewhat the wrong question. I almost never do resistance checks with my meter. I do mostly voltage checks, and for those I believe you want a meter with a very high internal resistance (going from memory here, since my reference material is all at home). Anyways, something new and expensive will be best. :-)