Test Equipment: DVM

A computer no longer appears to booting up...in fact the computer won't even POST. So is the computer failure a problem related to the motherboard, the CPU, or the Power Supply?

A DVM (Digital Volt Meter) in the hands of a skilled support technician can quickly be used to verify if a power supply is functioning correctly. How to use a DVM to diagnose power supply operation will follow later in the spring but for now let's cover what you should look for in a DVM.

That are many manufactures of DVMs; one of the better DVM manufactures is Fluke which builds a top-quality meter with a high end price (an entry level Fluke DVM exceeds $125). What I will say about Fluke DVMs is that they can take a lot of physical abuse as well as electrical abuse and still be accurate. The Fluke Meter picture on the left is a Fluke 189 which even today sells at over $400 (the Fluke 189 has been replaced with the Fluke 289 which sells for over $550). Of course most people don't have $500 let alone $100 to spend on a Fluke meter so what are some other options?

The good news is that there are hundreds of models of low-cost DVMs to choose from! The meter listed on the right is sold via Harbor Freight under the CEN-TECH name (this is actually a MASTECH MS8228 meter...MASTECH is a OEM for many companies that sell DVMs) for just under $40 which offers features that even the high end Fluke does not offer! 

I am sure at this point you are wondering what are the differences between a $400 DVM and a $40 DVM? Without going into the details that most likely only people with an electronics background with understand the simple answers are: accuracy and over-load protection. 

In a nutshell a Fluke DVM will tolerate the operator measuring electrical properties incorrectly by simply "blowing a fuse". A inexpensive meter (this would include a CEN-TECH for example) will not tolerate incorrect electrical measurements and more than likely the end result would be a non-functioning meter! 

The good news is that as long as you don't take current measurements or have the meter set for resistance and then decide to place the meter probes into an electrical outlet the chances of destroying a low cost meter is small.

As for the DC voltage accuracy I was very impress to see that my low-cost CEN-TECH was within .025 volts of my high-cost Fluke when measuring small DC voltage! Best yet the CEN-TECH has the ability to measure RH (Relative Humidity), Temperature (both an internal temp sensor and external temp sensor are used), sound levels, and luminescent (light levels) can be measured! Not a bad meter for $40!

There are a ton of specifications that we can talk about when discussing DVMs but the goal of this page is to simply give you an idea about the differances between a high-cost and low-cost meter!




 

4 comments:

  1. BTW: I have seen the MASTECH version of this meter exceed $100! The CEN-TECH version of this meter is $40 and the specs are the same!

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  2. Update...the MASTECH meter has the capability to read Transistor Gain and test diodes...something that most computer techs don't do! So if you are an electronics person buy the MASTECH; if you are a computer person the CEN-TECH should be just fine!

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