High Burden Voltage, how much of an issue? (BK Precision BK2709B) - Page 1
Forum section: electronics / beginners

author: tryton8
author_rank: Contributor
timestamp: March 02, 2011, 08:24:54 pm
content: Hello!I have recently burned a very cheap multimeter and I wanted to get something better this time.I've watched entire $100 shootout and I liked BK Precision BK2709B the most due to fast autoranging and responsive continuity check. What puzzled me though is it's very high burden voltage. It has 500 ohms shunt resistor on the microamps range and 6 on the milliamps range, which is 5 to 10 times more than most others, making it a second worst on the shootout in this respect.Can somebody explain under what circumstances would this be an issue? I am still getting my feet wet with electronics so while I sort of understand what burden voltage is I don't have the knowledge to figure out in what cases it could become an issue.Also do you think this is big enough of a problem to go for Uni-T UT61E instead, which also has fast autorange and responsive continuity test?I will mostly be measuring battery powered circuits (3 to 5V) I build for school projects and as a hobby.Thanks in advance.

author: saturation
author_rank: Super Contributor
timestamp: March 02, 2011, 09:36:28 pm
content: The burden voltage on this B&K, from the users manual, is reported as 0.4V on 660uA, 66mA, 10A ranges and 2V on 6600uA, 400mA ranges.http://www.fluke.com/Fluke/sves/comunidad/fluke-news-plus/ArticleCategories/Electrical/BurdenVoltage.htm

author: tryton8
author_rank: Contributor
timestamp: March 03, 2011, 12:26:07 am
content: Hi saturation. Thanks for digging up those numbers but I'm afraid they don't help me much. And while the article was great and it did make the issue a bit clearer, I still am not sure when and how often (and how much) would any of this matter in real life.Dave made this seem like a big issue when he compared it to other meters (that had 5 to 10 times lesser shunt resistor values), but then he still declared that BK a winnerTo give you an idea of my current level of knowledge I am 14 and i had to google up ohms law 2 weeks ago.I got myself a book about basic electronics and I want to learn everythng about it because its what interests me, and thats why I want to buy a good meter that I can grow into.So Id really appreciate if someone would be patient enough to answer questions from my first post.

author: Simon
author_rank: Unknown
timestamp: March 03, 2011, 07:56:11 am
content: when you measure current in a circuit with a multimeter you put it in series with the circuit under test. So your putting a resistance in series with your circuit that will rob (burden) some voltage for itself due to the ohms law you recently found out about. Multimeters are designed to have as low resistance as possible so as to have as low voltage drop (burden voltage) when measuring current, it has to be something in order to make the measurement but as little as possible.Say you were measuring the voltage in a 5 V digital circuit. if your multimeter had a max burden voltage of 0.5V you would be loosing up to 10% on the voltage that gets actually supplied to your circuit. in the case of TTL logic it may fail to work as TTL chips have strict working tolerances.The specified burden voltage is a maximum. Because the amps range basically turns the DMM into a resistor (as seen by the circuit) the more current you are measuring the more the DMM will burden the circuit and have more voltage fall across it.

author: EEVblog
author_rank: Unknown
timestamp: March 03, 2011, 12:11:18 pm
content: Read the full article I wrote here:http://www.alternatezone.com/electronics/ucurrent/Yes, it got declared the winner, because in most general circumstances burden voltage is not hugely important, so it didn't rank high enough to count against it.Dave.

author: tryton8
author_rank: Contributor
timestamp: March 04, 2011, 02:42:48 am
content: Thannk you Dave and Simon! I had a feeling this doesnt matter much except in some specific situations, and even in those there seem to be ways to get around it.So I still ended up ordering BK, too many things i liked about the little thing.Cant wait to get it.