Multimeter for instrumentation

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Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I'm in the market for a new multimeter or meters. I don't do a lot of instrumentation but enough that troubleshooting signals would help. Any recommendations for products or what to look for? This will be partly coming out of my pocket, so cost is important. I've been looking for something that I could use for 4-20mA signals. Any clamp meter I've seen that boasts something with that resolution is either more money than is worth it for me (Fluke 771) or some cheapo on Amazon that I do not trust.
Thanks.
 
Before I retired I had an great Fluke VOM with a 1,000 volt megger ( for testing motors ) for over 10 years. Dropped it off a 6 & 8' step ladder a dozen times with no damage so I think Fluke is best in c!ass. Please stay away from any meter made in china. We had too many problems with them.( flimsy test leads, short life, ). I own 4 clamp on amp meters, 30 year old think its a model 78 from Fluke VOM & a 5,000 volt megger all.made in USA.
 
Is it ever at all useful or accurate to put the leads of a DMM in parallel with a 4-20mA signal for testing? I know the proper way is to put it in series, but that obviously requires breaking the circuit.
 
It can be- you can measure voltage across the sensor and see the voltage drop change as the value/current changes. Or, you can measure voltage across the display/input device, which probably has a fixed resistor inside, and calculate the current.
 
The key word is trust. A lot of stuff works. Who knows what's inside. I'm sure many are fine, but you don't know. I bought a cheapo moisture detector thing with the small pierce probes -- I'm fine with that. I wouldn't buy that company's multimeter.
 
Electromatic said:
Is it ever at all useful or accurate to put the leads of a DMM in parallel with a 4-20mA signal for testing? I know the proper way is to put it in series, but that obviously requires breaking the circuit.
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The whole four to 20 milliamp signal will pass through the meter because it's basically a short circuit compared to an analog input for instance. So as long as that will not create a process upset for the short period of time you have the meter inserted it works pretty well and is a whole lot easier than trying to open up the circuit which also could create a process upset.
 
Once upon a time, the resistance for any device reading a 4-20mA signal was 250 ohms. Reading the voltage across that resistor will give you 1V for 4 mA and 5V for 20mA. But now you can't rely on that. If you can find a data sheet on the device, you can figure out the mA for the voltage drop. And the circuit just might be 0-20mA, too.

One way you can put a meter in series on a 4-20 mA circuit without interrupting the process is to put the leads across a fuse in the circuit (IF there is one JUST for that circuit) and then open the fuse. Be sure to close the fuse before removing the leads.
 
Recently saw that some of Flukes cheaper meters are made in China. Will never own or use any safety or test equipment made in China. Our company thought they did us a favor by purchasing the electricians a cheap made in China capacitor tester that also had a few volt scales. I left mind in the box to collect dust. Coworker who only used it a few times in first 6 months and it broke. For fun I called the company to ask about warranty & where to send it for repairs. Da warranty? Told me they were throw aways. Since I stopped using the great old Simpson model 260's meters back in the 1970's never had a made in USA digital meters break .
 
hillbilly1 said:
Yeah, the 1507 is made in China.
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Wow. Thought only a few on the cheapest Flukes were made in China. As a patriotic Viet Nam vet I do not want to bring politics into this great site but go to extremes to not purchase china products. Did a search and the 1507 VOM/Megger was selling for $800 at one site ( $325 for a used one ). Proud to say that I only own 1 tool made in China. A replacement Craftsman breaker bar that I exchanged 20 years ago that I never used because I have a few USA made ones.
 
ptonsparky said:
I found both the T+ and the 1507 to be very good. The 1507 has a low ohms scale that is great. Good enough to find a shorted winding in a 100 HP. Not ground faulted.

I'm glad I don't have to choose a new one. Too dang many choices.
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Good to hear, I just received my 1507 today. $700. Retiring my old hand crank Biddle. Used it three times this month, and hasn’t been calibrated in probably 10 years, so it was time!
 
zbang said:
Oh, not that again.


Fluke makes some of their meters in China and you just might have one. (Got a T+Pro? Made in China.)
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I have one too ... Works great for the last several years.
When testing a circuit got too close to the 4S box and got grounded ... Thought it was "Toast", but it came through with battle wounds.
 
At the large ( 5 million square foot medical campus ) that I retired from both of the JCI ( Johnson Controls ) and a smaller control contractor all used Fluke meters. Judging by how dirty the rubber bumper cases were bet these meters were over 10 years old.
 
Electromatic said:
I'm in the market for a new multimeter or meters. I don't do a lot of instrumentation but enough that troubleshooting signals would help. Any recommendations for products or what to look for? This will be partly coming out of my pocket, so cost is important. I've been looking for something that I could use for 4-20mA signals. Any clamp meter I've seen that boasts something with that resolution is either more money than is worth it for me (Fluke 771) or some cheapo on Amazon that I do not trust.
Thanks.
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I use the705, 771 and the 789. the 789 does it all. But the 771 clamp makes life much easier when you can't shutdown process.
 
On the eevblog forums they have a section for multimeter reviews, and I think they even have a comparison list between many different models. You can read their forums without signing up for an account. The biggest problem with the really cheap meters with unknown brand names is that they don't meet the voltage standards they say they do. Many of the users on that forum say they'll happily use a $10 meter from China, as long as they're only measuring a few volts, but they won't trust it not to blow up when used at a higher voltage that is still within the stated specs on the meter, because the stated specifications are not true, for the very cheapest meters.
 
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