Advice on a new DMM

[jaimeroldan]

Hi guys
This is my first post here, and would like to say "Hola" to everyone.
I'm an undergraduated Electronic Eng. , and i would like to buy a new multimeter.
My budget is about a 100-120 bucks.
Features in order of magnitud are:
- Micro-Amps and Mili-Volts
- Decent accuracy for dc volts and ohms
- Relative Mode
- Autoraging
- Acceptable Capacitance acuraccy
- Freq. measurement to at least 1Khz
- Temp measurement (no a must, but a big plus)

Pluses:
- Computer Interface
- True RMS
- AC+DC (volts or/and amps)
- Inductance or Transistor gain (hFE) measurement


Thank you all for advice

[EEVblog]

If you want PC interface for $100 or so, you'd be looking at the Chinese brands like Uni-T

Dave.

[IanB]

If you are on a budget you might put the Radio Shack 22-812 on your shortlist, details here:

http://support.radioshack.com/productinfo/DocumentResults.asp?sku_id=22-812&Name=Search+Results&Reuse=N

It costs about $70 in Radio Shack stores typically, but it has in the past been offered at $50 for limited periods. It doesn't tick all of your boxes, but it hits many of them.

You can either use the computer interface software provided, or I wrote a simple logging program for Windows you can get here:

http://www.candlepowerforums.com/vb/showthread.php?261833-Playing-with-the-RadioShack-22-812-Meter&p=3326583&viewfull=1#post3326583

My code will work fine on Windows 7, but the Radio Shack software may not. The interface protocol is documented so if you feel like it you can modify my code or write your own.

[Tony R]

I once wanted a DMM with a computer interface, and i got one it cost me $80 or so after shipping, and i loved it for a while, but i found i never really used the computer interface part of it that much. and then it broke shortly after a year.

I looked at the radio shack one, i ended up getting one online from www.circuitspecialists.com, and looking back i would not recommend them anymore.

The radio shack one does not have an isolated PC connection, and it being a cheep DMM i would not trust it not to take out your computer.

ultimately, i reconsider the PC interface requirement, its good if you want to test how a battery drains, but i don't think you will find any use for it any time soon. Im not sure how many low end DMM will have a uA range.

I am a big fan of Fluke, the 89 is a good meter and hits everything in the required section (i got mine new for 314.44 on amazon.) No PC interface, is True RMS, does not have a AC+DC but its not hard to get that without the feature built in, and idk about anyone else, i don't trust the hFE tester on DMM, are you really going to use it that much anyways, plus what is hFE? its Ic/Ie, nothing you cant find without it

You may also find a used 189 or 187 on ebay for under or a little over 300, i know its above your budget, but it will do data logging and everything else you require.

[Kiriakos-GR]

an isolated PC connection

Are you talking about the IRDA to USB modem ?
If yes, some latest Mastech ones uses this too.

[IanB]

The radio shack one does not have an isolated PC connection

That is not true. The 22-812 has an optically isolated serial port with a thick plastic shield separating the serial port module from the rest of the meter. There is no electrical connection between the two parts of the meter.

Also the PC interface cable is included with the meter. I just looked at the (admittedly nice) Amprobe AM-270 and the PC interface is a $50 extra cost option.

and it being a cheep DMM i would not trust it not to take out your computer.

Does it go tweet tweet then? 

I think you are being rather unfair. It is not an expensive meter compared to some, but the construction is tidy and the case is solid. For instance all the case screws are captive so you can't lose them and they screw into metal inserts. And it comes with spare fuses for the mA and A ranges included inside the case.

Another thing, the meter uses a 9 V battery and the battery lasts forever. I just measured the current draw at 0.95 mA. I've had the same battery in there for months and taken hours of computer logging measurements and it still reads 9 V.

[Tony R]

That is not true. The 22-812 has an optically isolated serial port with a thick plastic shield separating the serial port module from the rest of the meter. There is no electrical connection between the two parts of the meter.

It is always possible i am wrong, i do not see any documentation saying it is isolated, the serial cable hooks directly up to a standard dsub 9 connector, unless they have internal isolation which they should state if they do. Every other DMM i have found had a optical coupling between he meter and the computer. As far as i can see, this does not, and it is still going to take out a computer if that meter experiences any high transients. Can you please show me documentation as to this being electronically isolated?

Does it go tweet tweet then?

You know its one thing to debate and disprove on the facts of ones arguments, its another to point out simple spelling errors, yes I make a lot of spelling errors.

[elliott]

That is not true. The 22-812 has an optically isolated serial port with a thick plastic shield separating the serial port module from the rest of the meter. There is no electrical connection between the two parts of the meter.

It is always possible i am wrong, i do not see any documentation saying it is isolated, the serial cable hooks directly up to a standard dsub 9 connector, unless they have internal isolation which they should state if they do. Every other DMM i have found had a optical coupling between he meter and the computer. As far as i can see, this does not, and it is still going to take out a computer if that meter experiences any high transients. Can you please show me documentation as to this being electronically isolated?

I have one that is 10 years old, it is definitely optically isolated, I've had the thing apart numerous times to change fuses. The main board stays with the front half of the case, the serial port stays with the back half and there are no wires connecting them, just an LED.

[IanB]

That is not true. The 22-812 has an optically isolated serial port with a thick plastic shield separating the serial port module from the rest of the meter. There is no electrical connection between the two parts of the meter.

It is always possible i am wrong, i do not see any documentation saying it is isolated, the serial cable hooks directly up to a standard dsub 9 connector, unless they have internal isolation which they should state if they do. Every other DMM i have found had a optical coupling between he meter and the computer. As far as i can see, this does not, and it is still going to take out a computer if that meter experiences any high transients. Can you please show me documentation as to this being electronically isolated?

You can either go by my first hand knowledge stated above, having taken the meter apart and examined it, or you can believe some sales blurb found on the net somewhere. I am telling you it is isolated. The serial port module is on the back case of the meter, surrounded by a plastic shield, and connected only with an LED through the transparent plastic window. There is no electrical connection between the two halves of the meter.

[SgtRock]

Dear IanB and Tony R:

--It may be that your are both right. I am not inclined to disbelieve IanB's eye witness testimony. In as much as IanB's unit is 10 years old, perhaps Radios Hack has changed the design. Check out this current picture:

http://www.bz1-img.com/images_customers/04/41/4972737_46353_raw.jpg

--I have not yet figured out how to post a picture. If someone could point me to a post which explains how, I would appreciate it. In any case, it seems the current model 22-812 does not have optical, isolation. See the below link for the current manual:

http://support.radioshack.com/productinfo/DocumentResults.asp?sku_id=22-812&Name=Search+Results&Reuse=N

To IanB:

--In this case I have chosen to believe you and "my lying eyes".


"Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP Labs

Best Regards
Clear Ether

[IanB]

Dear IanB and Tony R:

--It may be that your are both right. I am not inclined to disbelieve IanB's eye witness testimony. In as much as IanB's unit is 10 years old,

It is elliot's unit that is 10 years old. Both of my units are new.

perhaps Radios Hack has changed the design. Check out this current picture:

http://www.bz1-img.com/images_customers/04/41/4972737_46353_raw.jpg

--I have not yet figured out how to post a picture. If someone could point me to a post which explains how, I would appreciate it. In any case, it seems the current model 22-812 does not have optical, isolation.  See the below link for the current manual:

I can find nothing in any of the documents linked there that say "the 22-812 does not have optical isolation". In fact, as Tony points out above, optical isolation is a standard feature that you expect to find in a meter.

http://support.radioshack.com/productinfo/DocumentResults.asp?sku_id=22-812&Name=Search+Results&Reuse=N

If you look at the exploded diagram at that link, the serial interface module is part 21 and the plastic insulating shield is part 6. There are no wires or connectors going to the serial interface module.

To IanB:

--In this case I have chosen to believe you and "my lying eyes".

Your confidence is heart warming, but unnecessary. It is widely documented across the Internet by owners of this meter that it has optical isolation. I am not the first to report it.

[SgtRock]

Dear IanB:

--Your answer is a nonsequitur. Sir, would you please look at the picture link I posted and tell me what you see?

"Three weeks in the lab will save you a day in the library every time" Stanley Williams, HP Labs

Best Regards
Clear Ether

[IanB]

Your answer is a nonsequitur. Sir, would you please look at the picture link I posted and tell me what you see?

I did look at the picture. It shows a meter that looks rather similar to the one I own alongside a collection of USB and Bluetooth adapters.

You need to be more specific with your comments. What conclusion would you like me to draw from that picture?

[gregariz]

I use the serial function rarely to log temperature over time but I have one of these when I do

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_117373_-1

It is also optically isolated, the aquisition rate is slow - but for my purposes that is fine.

[SgtRock]

Dear IanB:

I would expect you to draw the conclusion that I am an ass, and you would be correct. I was confused by the fact that your link to the manual is a dead link. The one I provided is working, but their is no legend explaining the parts in the exploded diagram. Also I can find no place in the manual where it says anything about optical isolation. But I did finally find a sale listing (see below) where it officially mentions optical isolation.

http://milo.com/pc-interface-46-range-digital-multimeter

--I am very glad I keep a civil tongue in my mouth as it makes eating crow so much easier. Finding no mention of isolation in the manual I assumed there was none. It it kind of an important feature to neglect mentioning.

--"If it weren't for Philo T. Farnsworth, we'd still be eating frozen radio dinners. Johnny Carson

Best Regards
Clear Ether

[ziq8tsi]

unless they have internal isolation which they should state if they do.

Quite the reverse.  Anyone buying a handheld DMM with PC interface should be entitled to assume that it is optoisolated.  In the extremely unlikely event that the design is an accident waiting to happen then there should be very stark warnings to that effect all over the documentation.  ("Keep hands clear of the lethal Dsub during use.  Never attach the PC interface when the common probe is at any non-ground potential.")

[IanB]

I was confused by the fact that your link to the manual is a dead link.

I didn't know it was a dead link, I've fixed it now. Thanks for pointing that out.

The one I provided is working, but their is no legend explaining the parts in the exploded diagram.

It is true there is no legend, but as I have taken the meter apart I was able to describe in my post which items on the diagram are the computer interface as an aid to the viewer.

[Tony R]

I shall admit that they it is optically isolated, it is not your standard isolation that most DMM have. I still stand by what i said earlier though. I would save the money and go for a good brand.

[SgtRock]

To All:

--Ding, ding, ding...The winner and still standing after ten rounds, by a KO, the Battling Brit from California, Ian the Bruiser B.

"Marconi invented the radio but he had to wait years and years till anything decent was on." Johnny Carson

Best Regards
Clear Ether

[Kiriakos-GR]

To All:

--Ding, ding, ding...The winner and still standing after ten rounds, by a KO, the Battling Brit from California, Ian the Bruiser B.

Add in the losses the original thread starter ... LOL 

[jaimeroldan]

Well i'm here.
But i didn't like how this thread turn out ...
On topic ...
I saw yesterday the Uni-Trend UT61C, for about 69 USD. Keep in mind that i live in Colombia (South America)
It meets almost every single criteria, the downside is that it doesnt have true RMS, but well i can live without it.
Theres a second hand fluke 189, for 320 USD, but its wayyyyyyyyy over my budget.
I will keep searching!

[Kiriakos-GR]

Well if you plan to work with battery powered devices, yes you do not need True RMS.

[Tony R]

Quite the reverse.  Anyone buying a handheld DMM with PC interface should be entitled to assume that it is optoisolated.

Excuse me for not assuming things are isolated, I for one do not assume the power is turned off because I want to cut a high voltage line, why would i assume its isolated? People get hurt all the time because they assume things.

but on topic again,  you mentioned the UT61C for 69 found one for cheaper... http://www.dealexcel.com/unit-modern-digital-multimeters-ut61c-dmm-dvm-dtm_p368.html and if i am reading it right it will be $15 to ship it to Colombia so that makes about 65... so not much cheaper

This one is like the cheap one i used to have http://www.radiolabs.com/products/electronics/meters/digitalmultimeter.php, one thing with the one i used to have the continuity buzzer started to fail and the buttons lost there sensitivity, but maybe they fixed it in this one...

Even cheaper: http://www.amazon.com/TekPower-TP4000ZC-RS232-Interaced-Ranging-Multimeter/dp/B000OPDFLM but i do not see anything about optical isolation, and i don't want to assume that it is. On the plus side it gives a pretty good documentation if you wanted to write your own data collection software.

http://www.amazon.com/Tekpower-Digital-Multimeter-Interface-DT9602R/dp/B000E2422G is another one, but i do not see that it comes with software, and i do not see anything saying how it transmits the data.

[Wartex]

Hi guys
This is my first post here, and would like to say "Hola" to everyone.
I'm an undergraduated Electronic Eng. , and i would like to buy a new multimeter.
My budget is about a 100-120 bucks.
Features in order of magnitud are:
- Micro-Amps and Mili-Volts
- Decent accuracy for dc volts and ohms
- Relative Mode
- Autoraging
- Acceptable Capacitance acuraccy
- Freq. measurement to at least 1Khz
- Temp measurement (no a must, but a big plus)

Pluses:
- Computer Interface
- True RMS
- AC+DC (volts or/and amps)
- Inductance or Transistor gain (hFE) measurement


Thank you all for advice

Amprobe 38XR has ALL that (except hfe).

[Lightages]

Based on my experience with UNI-T, I would not recommend them without reservation. I have a UT71E, their supposedly top of the line at around $200, and its accuracy was worse out of the box than my UT33C which cost me $16.

I have no experience with Protek, but this one:
http://www.tequipment.net/Protek608.asp
is only $9 more than your budget and meets everything you want as far as I can see. It also seems to get some positive comments where I have been able to find any reviews. As far as its build quality and safety I cannot comment. If it actually meets its specifications and has decent build quality, it is a bargain.

Oops: I see it does not have transistor HFE, but otherwise it has everything I think.