Questions and answer for the multimeter users

Some questions asked by meter users, we have the answers for you...

Q: I find no reference in your DMM terminology or FAQ regarding the difference between meters with 3.5 digits vs. meters with 3-3/4 digits vs. 4.5 digits. What does that mean to the user? I've never been able to get a real answer to this question.

A: Yes, many people get confused by 3 1/2, 4 1/2 .. digits. If you look at any DMM, it has a LCD display, this display has 8-segment numbers on it, but not all meters has the same number on it, ( there are many numbers hid inside when they do not have to show up), so the digits on the LCD will give you the capability of showing accuracy and resolution.

The regular LCD display shows 3 full digits, but a ONE in the first front of all the 3 digits, it shows 1999 , the max. If it shows 999 only, we say it 3 digits, but it shows 1999, so it is called 3 and half digits.

So, when you see a meter read the Max 19999, it is 4 1/2 digits. If you see some meter with X999, the X is a number that shows only a part of a 8, so we call it 3 3/4 digits.

This kind of display shows the ability of a meter to represent you resolution or accuracy.

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 and discussion center for the home can be found at HomeCentral.com. Click the
following link:

http://www.homecentral.com/
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 low as $25.99 Clamp meters are the most versatile meters for the home, as they can easily measure amps, volts, and resistance.

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