Just Handheld's measurement pro has all the answers to your toughest measurement problems.  Send your questions to support@justhandhelds.com or read through how he's helped others.  Below are some recent Q&A discussions, as well as some helpful links:

Links:

how to use a multimeter
automotive applications
java applet
DMM safety
basic electrical theory for boaters

Q: I've just ordered a Tecpel 8020 digital multimeter with capacitance.  I would also like to get a high voltage probe that will function with it, however most of the high voltage probes I find simply state that they will work with any multimeter with an input impedance of 10Mohms, your specification of the 8020 state that it has an input impedance of 20Mohms - how will this affect my finding a HV probe for this meter?  Please help.

A: In general, the meter's input impedance should always be much, much higher than the source impedance of the device under test.  When evaluating input impedance of a multimeter, therefore, the higher the value the better.  A meter with an input impedance spec of 20Mohms will have less "loading error" on the measurement than a meter with a spec of 10Mohms, therefore produce a more repeatable result.

The 10Mohm spec of your high voltage probe refers to the MINIMUM requirements of the meter that you use it with.  If you tried to use it with a meter that had a 1Mohm input impedance, you would get very inaccurate readings.

Bottom line - go ahead and use the high voltage probe you have in mind...it will work fine with the Tecpel 8020.

Q:  Can you recommend a good on-line guide for using a DMM, especially for around the home applications?

A:  A good basic guide for the home can be found at HomeCentral.com.  Click the
following link:

http://www.sierra.com/sierrahome/homedesign/howto/record/0,1179,558,00.html

In addition, the following sites have good info on basic theory and use of
multimeters.  The principles described can easily be applied to in-home
applications:

www.boatsafe.com/nauticalknowhow/electricity2.htm

www.users.dircon.co.uk/~doctron/meter.htm

Q:  Is it possible to use a DMM to measure the total load being drawn on a given circuit?  For example, can you use the meter on a normal 110VAC plug or lighting fixture to see how many amps are being pulled by other devices on the circuit? The problem is that I share circuits with other offices and would like to know how many amps I have left to play with - I don't want my computer on a circuit that has a fridge or air conditioner etc on it.

A: All 120V receptacles on a circuit are connected in parallel, therefore all will read 120V.  The current draw of each "leg" of the circuit will be different, depending what is connected (i.e. the refrigerator, computer, etc.)  Total current draw of a given circuit is is the sum of each "leg" , and is limited by the circuit breaker in the electrical box.   There are a couple of ways you can determine how many amps are left:

1.)  Determine which receptacles are on your circuit, and measure the current draw of each appliance, light, or device that is plugged-in.  Sum the total, and compare to the rating of the circuit breaker that is used (in the breaker box).  This is a very easy measurement to make with a Clamp-Style DMM.

2.)  Determine which circuit breaker is used for your office, and measure the current draw at the breaker.  Measuring here will give you the total current draw of the circuit (assuming all devices are plugged-in and operating).  Again, a Clamp-Style DMM will make this job easy.

In each of the above cases, subtract this total current draw from the circuit breaker rating to determine how much "capacity" is left in your circuit.

We have a variety of Clamp Meters available that can do this job, with prices starting at around $75.  Clamp meters are the most versatile meters for the home, as they can easily measure amps, volts, and resistance.