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Author Topic: Looking for suggestion for a good DMM  (Read 1389 times)
AE7UT
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Posts: 60




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« on: July 04, 2012, 10:54:48 PM »

I'm a farily new ham and have built 2 kits recently.  A Kendricks Scout Regen receiver and a Ten-Tec 1225 SWR wattmeter.
Both of these required a DMM to check the building or calibrate them.  I got a cheap Walmart DMM and it works but seems to lack the accuracy I need for calibrating the wattmeter. 

I would like a to stay under $200.  I know of Flukes but not sure which to look into.  Any suggestions would be great.

Thanks

Stan AE7UT
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KA4POL
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Posts: 1914




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« Reply #1 on: July 04, 2012, 11:20:44 PM »

This like similar questions for a good transceiver or anything else is provoking lots of comments. Therefore just some general remarks.
Besides, of course, AC/DC and Ohm measuring capabilities you might consider some add ons like basic transistor data, frequency, capacitance and inductance. All in one will possibly be outside your cost scope. Fluke is certainly a good choice. I just checked out the Fluke 117. It should be within your requirements as many others will be.
Set up a matrix with all abilities and check what is available. Most important are the tolerances. This is where quality shows.
Next thing to consider is an oscilloscope etc etc...  Grin
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AC5UP
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Posts: 3825




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« Reply #2 on: July 04, 2012, 11:57:36 PM »

I bought a new Fluke 77 30-ish years ago that continues to work well and has only been worked on once... The elastometric jumpers between the PC board and LCD display needed cleaning. The symptom was poor display contrast and had no effect on the accuracy of the meter. If and when I decide to have the accuracy checked the meter has exactly one adjustment: Apply 3.000 VDC from a precision source to the DC volts function and adjust until the meter reads 3.000 volts. Done, the entire unit is now calibrated.

If I was in your position I wouldn't hesitate to invest in a decent Fluke on the assumtion it's a "lifetime" meter, because it may well be.

OTOH, wouldn't hurt to look here: http://www.amprobe.com/Amprobe/usen/Home/default.htm

Plenty of bang for the buck with a good assortment of meter styles and features.
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KA1MDA
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Posts: 543




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« Reply #3 on: July 05, 2012, 03:47:33 AM »

I used to swear by the Beckman hardhat series of DMM's, especially for industrial use. They were pretty much indestructible. But then they sold off the line to Wavetek (I think) and those things were roral pieces of crap! I went through 3 of those at work in 2 years! Many of them failed or lost accuracy after barely being used. I would definitely avoid those!

Since then I've switched to Fluke. I accumulated 3-4 Fluke DMM's over the years, and they all still work with no problems. Try to avoid the "idiot" models- the ones with only 2-4 buttons on the front, and automatic everything. Those are designed for a "specialty market" (ie- use by barely trained, entry level field service people who have almost no concept of electrical measurements). Although the lure of auto everything may seem appealing, there are times when specialty measurements need to be made, and having full manual control over function and range selection is a big plus.

The newest Fluke I use is a work issued 3 year old model. One of the handy features it has is a LOW-Z mode, which drops down the meter impedance from 10 Mohms to 3K ohms. This basically makes it equivalent to an analog Simpson 260 style meter, which loads down the circuit to eliminate false readings from leakage through SCR's, quencharcs, etc. The Low-Z feature could possibly come in handy when working on older tube equipment.
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AC7ZN
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Posts: 41




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« Reply #4 on: July 05, 2012, 04:42:21 AM »

Hi Stan,

Even the cheapest DMMs these days have very good accuracy.  The ones you can get for less than five dollars at Harbor Freight have a basic accuracy of 1%.  What they lack is good quality and features:  their probes break easily and don't always make good connection--it is easy to damage them electrically or mechanically, etc.  The more expensive meters give you ruggedness and features such as auto-off so you don't waste batteries when you leave them on. 

If you can't calibrate your wattmeter with the DMM you have, it may not be due to inaccuracies in the meter but something else.  I'd hate to see you drop a hundred bucks on a Fluke meter only to find it reads the same!

Ask around and find a ham with a meter he trusts and try that before your ham radio dollars go to something you may not need...

73,
Glenn AC7ZN


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KE3WD
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Posts: 5694




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« Reply #5 on: July 05, 2012, 04:47:31 AM »

Hi Stan,

Even the cheapest DMMs these days have very good accuracy.  The ones you can get for less than five dollars at Harbor Freight have a basic accuracy of 1%.  What they lack is good quality and features:  their probes break easily and don't always make good connection--it is easy to damage them electrically or mechanically, etc.  The more expensive meters give you ruggedness and features such as auto-off so you don't waste batteries when you leave them on. 

If you can't calibrate your wattmeter with the DMM you have, it may not be due to inaccuracies in the meter but something else.  I'd hate to see you drop a hundred bucks on a Fluke meter only to find it reads the same!

Ask around and find a ham with a meter he trusts and try that before your ham radio dollars go to something you may not need...

73,
Glenn AC7ZN

My advice is to pay heed to what Glenn said here, took the words right out of my mouth. 

That Walmart DMM should be quite good enough to calibrate most Amateur Radio projects. 


73
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N4NYY
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Posts: 4742




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« Reply #6 on: July 05, 2012, 05:19:45 AM »

I use an Extech 430 True RMS. Has capacitor, freq measurements. Comes with Thermocouple for temp. I paid like $69. The nice thing is that it is kind of a jack of all trades. I used the temp to see if my A/C air was too warm.

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AA4PB
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Posts: 12683




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« Reply #7 on: July 05, 2012, 06:00:39 AM »

I have a hard time believing that the WalMart DMM is not accurate enough to calibrate the Ten-Tec 1225. The manual says that the voltages should be set within 5% of the specified value. Don't be concerned if the meter doesn't have as many digits as the value in the manual. Just get it as close as possible and check that the reading is withing +/-5% of the manual's value.

If you can borrow a good wattmeter from someone you can also do a comparison check to give you a "warm and fuzzy" feeling that what you have done is accurate.
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AE7UT
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Posts: 60




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« Reply #8 on: July 05, 2012, 02:12:45 PM »

Thanks for all of the replies.

I think the Walmart DMM is working OK but I had a hard time holding the probes on the right places while sending a signal through and making adjustments.  I think I'm looking not only for a good DMM but also one with interchangeable probes to help my clumsy efforts. I also plan on building more and also using test instruments more in my shack.

Thanks again.
Stan
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KE3WD
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Posts: 5694




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« Reply #9 on: July 05, 2012, 02:49:23 PM »

Thanks for all of the replies.

I think the Walmart DMM is working OK but I had a hard time holding the probes on the right places while sending a signal through and making adjustments.  I think I'm looking not only for a good DMM but also one with interchangeable probes to help my clumsy efforts. I also plan on building more and also using test instruments more in my shack.

Thanks again.
Stan


Better to invewt a small amount of pocket money in a package of alligator clip test leads. 

Even Rodeo Shark sells 'em.  In between the cellphones...


73
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