74
votes
Accepted
If I am measuring 2.3 V on a 1.5 V AA battery from Duracell, is my multimeter broken?
Most likely cause is that you need to replace the battery in your multimeter.
When the battery is very weak, the voltage drops to the point where the internal reference can no longer maintain ...
56
votes
How do we know that voltmeters are accurate?
These days, you build a primary voltage standard from a bunch of Josephson junctions and a microwave source. That generates a voltage that's dependent only on the defining constants of the ...
- 46.7k
48
votes
3.3M resistors not registering on multimeter - are they faulty?
Assuming you don't have a 20M range, put two of the identically marked 3.3M resistor in parallel on the 2M range, and you should read about 1.65M.
The "1" with the rest of the display blank means ...
45
votes
Accepted
Measuring current with a multimeter - What did I do wrong?
You placed an ammeter in parallel to a voltage supply, which created a short circuit through the meter and most likely blew the 10A fuse in the ammeter socket.
What you want to do is put the meter ...
- 1,330
45
votes
Accepted
Differences between oscilloscope, multimeter, and power supply voltage readings
When I set my power supply to 5V, the multimeter reads 4.995V and the
oscilloscope reads 5.02V rms.
5.02 V / 4.995 V = 1.005. That's a 0.5% difference. 5.00 V / 4.995 V = 1.001. That's a 0.1% ...
- 56.8k
40
votes
Why are multimeter batteries awkward to replace?
The internals of a well designed handheld multimeter are designed to contain any explosions that may occur from failing parts.
Imagine the following situation: you're holding a meter in your hand, ...
- 36.5k
37
votes
Accepted
Determine voltage drop over 10G resistors with cheap multimeter
Do what the ancients did ==== use a Wheatstone bridge. Like this
simulate this circuit – Schematic created using CircuitLab
Rotate the 10,000 ohm potentiometer for ZERO reading.
Then measure ...
- 34.6k
36
votes
Accepted
Capacitor Gaining Voltage Over Time?
What you've observed is called "dielectric absorbtion" or "recovery voltage phenomenon".
It's cause by kind of interia of the dipoles (ions) in the electrolyte while charging and ...
33
votes
Why isn't there any 9.5 digit multimeter or higher?
Four reasons:
Because modern meters have an autoranging function.
Because the dynamic range of the analog system would not support 91⁄2 digits, with a range of 1 V the noise floor would be in the ...
- 87.1k
32
votes
Why can't capacitors on PCBs be measured with a multimeter?
Why is this specifically a requirement for capacitors?
It's not. It applies to any and every component.
- 98.3k
30
votes
Accepted
What does the multimeter dial do internally?
This image (source) ought to tell you all you need to know about how it works. There are wiper contacts on the dial, shown at the bottom, that mate with pads on the meter's PCB.
These pads are ...
- 36.5k
30
votes
Accepted
Why can't capacitors on PCBs be measured with a multimeter?
If you do any measurement on a PCB, you are doing a measurement on the "whole circuit" instead.
If you know the schematics of your circuit, you will find some components where the influence ...
- 7,938
27
votes
Accepted
Can anyone identify this circut?
If you sum the capacitors to just one, then it looks like an envelope detector.
If you put capacitors in parallel then you can sum them together to just one.
$$C_{tot}=C_1+C_2+C_3+C_4$$
And then you ...
- 8,239
26
votes
How do we know that voltmeters are accurate?
From looking at the Wikipedia page for a voltmeter, it seems like something such as a Weston cell, which uses a reproducible and stable chemical reaction, is used as the ultimate reference voltage for ...
- 171k
25
votes
Accepted
When we should use only an "analog" multimeter?
You didn't ask for a complete exposition about the differences, so I'm not going to try and tabulate anything here. You asked about where an analog meter might be better (or should be preferred.)
...
- 78.5k
25
votes
Accepted
Why doesn't my multimeter show the correct Zener reverse voltage?
Because the limited current sourced by the meter is not enough to bias the Zener diode into the reverse avalanche region. Instead you are biased some where on the knee of the Zener reverse ...
- 57.6k
25
votes
Why are multimeter batteries awkward to replace?
It's a safety thing:
A multimeter needs to be safe to connect to the mains while holding in your hand, and there are stringent tests for this. One of the hardest to pass is that it must not spark to ...
- 7,854
22
votes
Why does most test equipment have 10 MΩ voltage input impedance?
Having worked with test equipment with a 100 MΩ input impedance, I can say that it does not only have advantages. It requires much more careful handling than normal voltmeters or scopes. For example, ...
- 321
21
votes
Accepted
Reasons not to use these leads
In addition to the excellent answer given by @JorenVaes there is also a simpler electro mechanical reason for this caution. If you take a close look at the lead connections for the 34xxxA multimeters ...
- 57.6k
21
votes
I am measuring a 9W LED with a clamp on ammeter. Why does it only draw 7.62W?
That user manual (which you should link to in your question) shows the following:
Figure 1. Just because it's digital, doesn't mean it's accurate.
You are measuring at the bottom end of the range ...
- 178k
21
votes
Accepted
Why does most test equipment have 10 MΩ voltage input impedance?
Remember that the actual ADC in the meter doesn't have infinite input impedance. It will source or sink some current on the voltage divider circuit. That means that raising the voltage divider ...
- 178k
19
votes
Accepted
Accuracy of a multimeter over 10 years period
Generally that figure is defined because you are supposed to calibrate your equipment annually.
If you don't.. all bets are off.
You can not extrapolate from one to the other, plus aging will not ...
- 46.9k
19
votes
What does the multimeter dial do internally?
An old analog meter may be easier to understand (source http://fourier.eng.hmc.edu/e84/labs/lab1/node1.html):
Since the gauge deflection depends on the current passing it, and the deflection/current ...
- 8,567
19
votes
5V LDO blowing up only when testing current draw
I think people are distracted by the PMOS, but the real reason is a voltage spike when the 24V is connected, due to inductance of the wiring that is even higher when the multimeter is connected, ...
- 2,715
19
votes
Accepted
What does the horizontal bar indicate in the DMM display?
That bar at the bottom of the screen simulates an analog meter - the length of the bar increases with increasing digital readings. It is often easier to observe a varying voltage by looking at the ...
- 60.2k
18
votes
why does my voltage regulator produce 5.11 volts instead of 5?
If you look in the datasheet you find that the output voltage of the 7805 can vary between 4.8 and 5.2 volt. This is the error margin of the output voltage.
Remember that in every design there is ...
- 3,940
17
votes
Is there any advantage to have a dedicated hole to measure milliamperes on a multimeter?
Meters are often left connected to voltage sources for purposes of monitoring them. Further, they often use the same knob for both mode selection and power on/off. If a meter uses the same knob to ...
- 47.1k
17
votes
Accepted
Please help me debug my circuit
You have diode D2 installed backwards:
The blue/green arrow points to the banded end of the diode as marked on the PCB. The red arrow points to the banded end of the diode as you have installed it.
...
- 73.1k
17
votes
Did a blown fuse in my multimeter damage my multimeter?
That's the whole idea of a fuse, to protect the device that it is deployed in. So no, tainted is all in your mind. Change the fuse and learn from the mistake, and welcome to the world of electronics!
...
- 1,609
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