Hi, I've been doing most of my automotive work (repairs, maintenance) and have been doing fine with most of that. But now I'm venturing into more electrical issues -- for example, I have been diagnosing some starting issues and have needed to take various electrical measurements and am trying to get a better understanding of circuits and the relationship of voltage, current, etc.
First of all the guides here are simply amazing. I can't believe this information is all in one place, freely available. Thank you!
My questions relate to the use of multimeters, I think I am starting to "get it" to some extent and would like to make sure I really understand some things that have happened and that I've read. For the most part I'm trying to answer my own questions but would like validation to see if I really do get it.
For some background, I've got 4 DMMs: a Harbor Freight cheap-o, 2 Craftsman, and an Equus 3320. The Equus I purchased recently, the others I've had for years. Well, after using them for a bunch of measurements recently I opened them all up and found that the fuses were blown in most of them so I think in years past I've probably done some stupid things without knowing what I was doing. I'm pretty sure I know "what not to do" now but would like to validate my understanding as well as test out the DMMs to make sure that they still operate properly and give valid results (once I replace the fuses).
With that, on to my questions!
1. For what types of measurements should I de-energize a circuit prior to attaching the meter? If I'm correct, it's:
- resistance
- continuity
- diode tests
Is that right? I can/have RTFM but I haven't found anything that explains "why" and that leads to my next question:
2. Why must the circuit be de-energized for the above and not for things like Voltage tests? Is it because the meter, in these modes, builds a low-resistance/impedance circuit within itself and essentially creates a short circuit?
3. Why is it OK to keep the Positive lead in the mA (low current measurement) jack when testing for Voltage even on high-current circuits? Is it because when in Voltage mode it creates a high-resistance circuit which is not the path of least resistance and therefore the majority of the current won't flow through the meter?
4. When the meter is connected in parallel, such as when measuring voltage, why does any current at all flow through the meter and therefore cause voltage to register? In other words, if the DMM is a high-resistance alternative path, why is it possible to get any kind of voltage reading if the current doesn't pass through the device?
5. I noticed the DMM still registers continuity and resistance, even though the fuse is blown. Does that make any sense? I would have thought there would be an "open" in these modes and that these modes would no longer work with a blown fuse.
6. Is the fuse (when in the fused positive jack) only crossed when the DMM is set to explicit current measurements or does it typically protect other "current-style" tests such as continuity, resistance, and diode? (Related to the above question.)
7. Is there anything other than the fuse that I can/should look at to see if my meter's been damaged by past, stupid errors?
8. What's the best way for me to validate all the meter functions, should I just check each function against known voltage/current sources and compare against another meter?
I should add, since I'm new to this forum, that if this is not an appropriate place to ask these level of questions please let me know.
Thanks!
First of all the guides here are simply amazing. I can't believe this information is all in one place, freely available. Thank you!
My questions relate to the use of multimeters, I think I am starting to "get it" to some extent and would like to make sure I really understand some things that have happened and that I've read. For the most part I'm trying to answer my own questions but would like validation to see if I really do get it.
For some background, I've got 4 DMMs: a Harbor Freight cheap-o, 2 Craftsman, and an Equus 3320. The Equus I purchased recently, the others I've had for years. Well, after using them for a bunch of measurements recently I opened them all up and found that the fuses were blown in most of them so I think in years past I've probably done some stupid things without knowing what I was doing. I'm pretty sure I know "what not to do" now but would like to validate my understanding as well as test out the DMMs to make sure that they still operate properly and give valid results (once I replace the fuses).
With that, on to my questions!
1. For what types of measurements should I de-energize a circuit prior to attaching the meter? If I'm correct, it's:
- resistance
- continuity
- diode tests
Is that right? I can/have RTFM but I haven't found anything that explains "why" and that leads to my next question:
2. Why must the circuit be de-energized for the above and not for things like Voltage tests? Is it because the meter, in these modes, builds a low-resistance/impedance circuit within itself and essentially creates a short circuit?
3. Why is it OK to keep the Positive lead in the mA (low current measurement) jack when testing for Voltage even on high-current circuits? Is it because when in Voltage mode it creates a high-resistance circuit which is not the path of least resistance and therefore the majority of the current won't flow through the meter?
4. When the meter is connected in parallel, such as when measuring voltage, why does any current at all flow through the meter and therefore cause voltage to register? In other words, if the DMM is a high-resistance alternative path, why is it possible to get any kind of voltage reading if the current doesn't pass through the device?
5. I noticed the DMM still registers continuity and resistance, even though the fuse is blown. Does that make any sense? I would have thought there would be an "open" in these modes and that these modes would no longer work with a blown fuse.
6. Is the fuse (when in the fused positive jack) only crossed when the DMM is set to explicit current measurements or does it typically protect other "current-style" tests such as continuity, resistance, and diode? (Related to the above question.)
7. Is there anything other than the fuse that I can/should look at to see if my meter's been damaged by past, stupid errors?
8. What's the best way for me to validate all the meter functions, should I just check each function against known voltage/current sources and compare against another meter?
I should add, since I'm new to this forum, that if this is not an appropriate place to ask these level of questions please let me know.
Thanks!