I have to measure current/voltage of an unknown circuit. So why should I start with the highest rating and gradually come to a smaller value to identify the current/voltage? What's wrong if I start with the small value to measure that current/voltage?
\$\begingroup\$
\$\endgroup\$
2
-
2\$\begingroup\$ I have a pot of soup. I wish to store it. I have a range of containers ranging from the very large to the very small. I will see if the soup can be contained in the containers by pouring it in. So why should I start with the largest and gradually come to a smaller value to identify the size of container? What's wrong if I start with the small value to find the best container. \$\endgroup\$– Russell McMahon ♦Commented Sep 26, 2012 at 2:23
-
2\$\begingroup\$ I have a valuable vase. I wish to display it in a shop window. I have some display stands. Some are very strong. Some are very weak. To find a stand that works OK but is not too too strong I will try several. So why should I start with the strongest and gradually come to a smaller value to identify the required strength? What's wrong if I start with the small value to measure that strength? \$\endgroup\$– Russell McMahon ♦Commented Sep 26, 2012 at 2:25
Add a comment
|
1 Answer
\$\begingroup\$
\$\endgroup\$
4
High voltage applied to a low voltage range may destroy the meter - and also may destroy you.
Low voltage applied to a high voltage range will not damage the meter, or you.
High current applied to a low current range may destroy the meter - and also may destroy you.
Low current applied to a high current range will not damage the meter, or you.
Added:
Note this stack exchange question which was asked about 15 hours after this one.
How do I choose the right replacement fuse for my multimeter?
Note that replacement is not trivial - as correctly advised by AndrejaKo.
answered Sep 26, 2012 at 2:27
-
3\$\begingroup\$ Most meters have built in protection circuits so it doesn't really matter; both over-voltage protection and over-current protection. The meter will display "overload" until you switch to a higher range. \$\endgroup\$ Commented Sep 26, 2012 at 4:09
-
3\$\begingroup\$ You don't know what multimeter he has. I, for one, burned one's ammeter function thinking that it has protection. It wasn't a "needle" one. It's always good practice to be safe first, just saying. \$\endgroup\$– VladCommented Sep 26, 2012 at 8:12
-
2\$\begingroup\$ @trav1s - MOST modern lower costs multimeters will, at a minimum, blow an internal fuse if overloaded by less than 2:1 on their 200 mA or below ranges. On the 10A or 20A rranges typical on cheap meters there is usually NO over-current protection. Note that few people have 200 mA fuses to hand and many people will not realise that a blown internal fuse has stopped all current ranges under 200 mA working. Thos who do replace the fuse may use more available 1A or 2A ones. Next time the meter itself may be damaged. \$\endgroup\$– Russell McMahon ♦Commented Sep 26, 2012 at 8:14
-
\$\begingroup\$ @trav1s - note that multimeter is not mentioned in the question - this may be a few simple analog ammeters/voltmeters of different ratings, an old analog multimeter, or a cheap digital multimeter with no proper internal protection (plenty of them exist) Without knowing exactly what he is using or what voltages/currents are being measured I think it's very important to err on the side of caution. \$\endgroup\$ Commented Sep 26, 2012 at 10:37