Tech specs for clamp meter stumping me

[PetrosA]

I'm in the market for a new everyday meter as an upgrade from my Extech EX820. I'm leaning toward a clamp meter for the versatility it offers as well as a somewhat lower price (a good DMM from Dranetz-BMI or Agilent with an Amp clamp is way more money than I can afford to spend right now, even if they do offer excellent accuracy).

So this time around I'm really looking at the spec sheets for a few different clamp meters. The spec that I need help understanding is the accuracy during AC current readings. The format is generally something like "2% ?5 digits" or "1% ?10 digits". I understand that the 1% is going to be more accurate than the 2% but how does the "? x digits" affect the statement? Is "2%?5digits" more accurate than "1%?10digits"?

Thanks.

 

[Volta]

I don't know how to answer your question though someone surely will.

My input is to be sure it is auto-ranging. I didn't on my last meter, I like it fine otherwise, but it is very frustrating to need to set the range to the expected result each time I use it to test voltage. Grrrr.

 

[PetrosA]

I don't know how to answer your question though someone surely will.

My input is to be sure it is auto-ranging. I didn't on my last meter, I like it fine otherwise, but it is very frustrating to need to set the range to the expected result each time I use it to test voltage. Grrrr.

Yeah, I definitely want it to autorange for the voltage. From what I'm reading though, a clamp meter with low and high ranges for the Amp readings are more accurate in their respective ranges than a meter with a single Amp range. Another thing I didn't know is that most clamp meters aren't worth much until the current is at least 5% of the scale. So if you have a 1000A meter, the readings below 50A might be way off. That would make troubleshooting a lot of things very difficult.

 

[Volta]

Seems believable. I don't have any complaint with adjusting to the right amperage range, compared to voltage anyhow.

 

[mivey]

I'm in the market for a new everyday meter as an upgrade from my Extech EX820. I'm leaning toward a clamp meter for the versatility it offers as well as a somewhat lower price (a good DMM from Dranetz-BMI or Agilent with an Amp clamp is way more money than I can afford to spend right now, even if they do offer excellent accuracy).

So this time around I'm really looking at the spec sheets for a few different clamp meters. The spec that I need help understanding is the accuracy during AC current readings. The format is generally something like "2% ?5 digits" or "1% ?10 digits". I understand that the 1% is going to be more accurate than the 2% but how does the "? x digits" affect the statement? Is "2%?5digits" more accurate than "1%?10digits"?

Thanks.

Suppose you are on the 600 volt scale with a one decimal place resolution and read 10.0 volts.

2% +5 digits = 0.02*10 + 5 x 0.1 => ?0.7 volts (?7%)
1% +10 digits = 0.01*10 + 10 x 0.1 => ?1.1 volts (?11%)

Now for a 500.0 volt reading:
2% +5 digits = 0.02*500 + 5 x 0.1 = ?10.5 volts (?2.1%)
1% +10 digits = 0.01*500 + 10 x 0.1 = ?6 volts (?1.2%)

It is different if the accuracy is given as a % of scale (normal for analog meters).

 

[PetrosA]

Suppose you are on the 600 volt scale with a one decimal place resolution and read 10.0 volts.

2% +5 digits = 0.02*10 + 5 x 0.1 => ?0.7 volts (?7%)
1% +10 digits = 0.01*10 + 10 x 0.1 => ?1.1 volts (?11%)

Now for a 500.0 volt reading:
2% +5 digits = 0.02*500 + 5 x 0.1 = ?10.5 volts (?2.1%)
1% +10 digits = 0.01*500 + 10 x 0.1 = ?6 volts (?1.2%)

It is different if the accuracy is given as a % of scale (normal for analog meters).

Assuming this works the same for current as it does for voltage, I was able to take two hypothetical readings and use them for comparison. The choice has been made Thanks Mivey!

 

[mivey]

Assuming this works the same for current as it does for voltage, I was able to take two hypothetical readings and use them for comparison. The choice has been made Thanks Mivey!

Works the same. You're welcome.

 

[dbuckley]

And just in case its not obvious if you have a four digit display then the plus or minus so many count is a smaller error than on a three (or three and a half, ie a leading '1') display.

 

[PetrosA]

In case anyone else needs it, I found this guy's vblog. He explains things in a pretty simple style and his reviews of various multimeters are fun to watch. In this clip he explains the difference between resolution and accuracy in DMMs.

http://www.youtube.com/watch?v=U4JFeU-o2kc