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Questions tagged [measurement]

Measurement is the assignment of numbers to objects or events. All measurements consist of three parts: magnitude, dimensions (units) and uncertainty.

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29 votes
3 answers
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Can an oscilloscope be used as an EKG?

I was at my doctor's office and noticed an EKG machine that looked like a standard oscilloscope. In fact, its case was almost identical to my dual channel Tektonix 1104b. The main difference was that ...
user148298's user avatar
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25 votes
5 answers
5k views

Help learning from a mistake connecting an oscilloscope

I have built this circuit to dim a lamp with a PWM signal. It had an issue where the MOSFET was getting really hot. So I wanted to know what was happening on the gate of the MOSFET. I turned the PWM ...
cyrili101's user avatar
  • 409
24 votes
13 answers
6k views

Level of a water tank with a microcontroller

How do i measure the level of a water tank with a microcontroller?
mad_z's user avatar
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20 votes
13 answers
10k views

Why only sine waves?

I have already read a few EE texts where a sine wave is often seen. Why is the sine wave often used as a test function for a circuit or a system? Why don't we use any other signal instead of sine? ...
DSP_CS's user avatar
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20 votes
5 answers
4k views

Why is this meter giving different readings depending on its orientation?

My newly-restored (re-capped) 1950s vacuum tube voltmeter is now operational...but there's one further issue. The meter gives correct readings when lying on its back, but when oriented vertically- as ...
Simon Owen's user avatar
19 votes
3 answers
4k views

Why do digital scopes sample signals at a higher frequency than required by the sampling theorem?

In the quest for a not so expensive PC scope/logic analyzer, I have found a nice little device it looks very well done and I know it will do the job. However looking at the specifications, I ...
LuisF's user avatar
  • 649
19 votes
4 answers
2k views

How can I measure the temperature wirelessly inside a piece of meat?

For a cooking experiment, I'd like to be able to measure the temperature inside a piece of meat while it's being cooked. Due to the mechanics of the cooking process, it's going to be difficult to use ...
Rocketmagnet's user avatar
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18 votes
6 answers
8k views

Why are oscilloscope input impedances so low?

My question is two-fold: Where does the input impedance come from? I'm wondering where the input impedance of your average multimeter or oscilloscope comes from? Is it just the input impedance to ...
PersonWithName's user avatar
18 votes
1 answer
3k views

How does the network card determine the cable length?

I have an older Gigabyte Technology GA-MA770T-UD3P motherboard with an on-board network card described like this: ...
U. Windl's user avatar
  • 333
17 votes
3 answers
5k views

What kind of oscilloscopes are qualified for measuring USB 3 Super Speed Signals?

I understand that they probably will be very expensive. But I have little idea of what kind would qualify. How much bandwidth? At what sampling rate? Any other parameters?
J.L's user avatar
  • 173
17 votes
7 answers
129k views

Physically determine unknown wire's gauge

Is there any way to easily and accurately determine the gauge of stranded wire by measuring it? I know you can pretty easily determine the gauge of solid-core wire with just a pair of calipers by ...
Connor Wolf's user avatar
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17 votes
4 answers
67k views

How do I measure differential signals (like RS-485 or DMX) on an oscilloscope?

I've encountered differential signals in a few places, such as a differential output audio amplifier and now in a project working with DMX which is similar to RS-485. (Here's a similar question about ...
JYelton's user avatar
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16 votes
12 answers
47k views

Ways to determine polarity (dc) without a meter

I came across this question about how to figure out the polarity of a cell phone charger without a meter. This made me think of what methods you could use to figure out the polarity other than using a ...
Garrett Fogerlie's user avatar
15 votes
3 answers
3k views

How can I measure gate capacitance?

Is there an effective way to directly measure the gate capacitance of a power MOSFET, like say the IRF530N? The way my circuit is behaving would indicate that the effective gate capacitance is ...
scanny's user avatar
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15 votes
2 answers
19k views

What are the differences between a x1 and a x10 oscilloscope probe

I've heard pros of x10 oscilloscope probes a lot. Now I need to know the cons, but I couldn't find a clear explanation. Some people say x1 probe is for small signal. How do you decide either x10 or x1?...
ryunika's user avatar
  • 153
15 votes
2 answers
6k views

How do you calculate the noise of an op-amp circuit?

I think I know how to do this, but you can find a lot of different instructions and calculators online that contradict each other. I have yet to find a clear, concise procedure for calculating the ...
endolith's user avatar
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15 votes
2 answers
1k views

Why am I getting odd inductances from home made inductor?

This question is related my my previous question: What to do about very hot planar inductor? What I'm trying to do I am trying to make a planar inductor (made from the tracks of the PCB, and ...
Rocketmagnet's user avatar
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14 votes
7 answers
2k views

Measuring small movements of a needle and syringe

My question is how to measure very small movements of a needle and syringe when injecting. When doctors inject local anaesthetic, they always aspirate (suck back) first to make sure they are not in a ...
Mark Stoneham's user avatar
14 votes
3 answers
15k views

Methods to measure inductance with high (1%) precision using standard equipment?

I am modeling the fine behavior of interacting oscillatory circuits. I have looked up a couple of methods for measuring inductance. I believe I am following the procedure faithfully, but the values I ...
KBL's user avatar
  • 313
13 votes
4 answers
3k views

Why does it take time for electronic scale to measure?

If I am standing on a digital scale or measuring the weight of my luggage, the display doesn't show the weight immediately - it takes a few fractions of a second. Why is that and can you overcome it ...
Sharon G's user avatar
  • 147
13 votes
7 answers
22k views

What does a half-digit mean in case of accuracy?

What does it mean when somone says something like "3 and 1/2 digit" in case of accuracy of test equipments (or maybe A/D converters?) Can somone explain this a bit with some numbers as ...
Dumbo's user avatar
  • 3,284
13 votes
2 answers
15k views

How do you get eye diagrams?

I understand that eye diagrams give an indication of the quality of a signal. But I don't understand how they are displayed on an oscilloscope. With proper triggering shouldn't you get either positive ...
Peter Galleyn's user avatar
13 votes
7 answers
6k views

Soil moisture measurement

Background To kick-start my longstanding ambition of getting back into electronics, I decided to try and make a device that measures the soil moisture of potted plants to determine whether they need ...
drxzcl's user avatar
  • 3,785
13 votes
1 answer
4k views

Measuring ferrite core parameters

I have large amounts of inductors and transformers from power supplies or other undocumented sources. They are of course completely unmarked and I have no idea what kind of ferrite material they are ...
jpc's user avatar
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12 votes
6 answers
6k views

Why can't capacitors on PCBs be measured with a multimeter?

While looking at this article, it mentioned that one cannot test the capacitance of a capacitor while it is on a PCB. The explanation given is: The reason is, that when a capacitor is inside the ...
HFOrangefish's user avatar
12 votes
4 answers
5k views

DIY Oscillosope probes

I am interested in making my own cheap (somewhat disposable, or permanently attached to prototypes) probes for my oscilloscopes. In complex circuits, and dense PCBs sometimes it may be difficult to ...
Fotis Panagiotopoulos's user avatar
12 votes
6 answers
4k views

Measuring frequency of a signal above 5V with a microcontroller

I want to measure the frequency (up to 300 Hz) of a rectangle signal, that varies between 0V and Vtop, where Vtop is anything between 5V and 15V. Because I cannot apply more than 5V to the ...
PetPaulsen's user avatar
  • 2,343
12 votes
4 answers
17k views

Digital bathroom scale circuit - how it works?

I'd like to understand how the digital bathroom scales work. I was able to gather that there are four three-wire load cells connected into the Wheatstone bridge as suggested below. The load cells have ...
YSN's user avatar
  • 299
12 votes
2 answers
4k views

Measuring average current with uC and current shunt

This is my first post. I'm a software guy trying to do hardware so be gentle :) Circuit I'm designing a small circuit (see pic, and sorry for messy schematic) that plain and simply is a bunch of ...
ltj's user avatar
  • 163
11 votes
3 answers
16k views

How to measure electrical noise?

Another question I asked about Power Supply Noise pushed me to ask this question. The background is as follows: I have a design with PD (Photodetector) and Opamp at medium frequency (couple hundred ...
Frank's user avatar
  • 2,862
11 votes
2 answers
4k views

Audible difference between "audio grade" capacitors in the same range?

The following is a list of prices for some capacitors sold by Mundorf, a massively audiophile-approved component company. Each capacitor is within the same product range ("EVO"), and apart from some ...
abza's user avatar
  • 664
11 votes
1 answer
13k views

How does autoranging work in a multimeter? What is the circuit?

I was curious how this is done. It seems you would have to vary the voltage and current to measure resistance from 1ohm to 10Mohm.
Bill's user avatar
  • 2,496
10 votes
2 answers
2k views

Reasons not to use these leads

I found the following note with a set of test leads we use for our Agilent 34461A[1][2]: This Test Lead Set is designed for use with the Agilent 34xxxA Multimeters, and also the U274A, U3401A, and ...
Mast's user avatar
  • 1,305
10 votes
3 answers
12k views

Understanding capacitance in oscilloscope probe tip

I am trying to understand the capacitance and resistance in oscilloscope probe tip. In the above attached image, that 9Mohm resistance is used for that 1x and 10x setting that divides the input ...
user avatar
10 votes
3 answers
3k views

How do I measure the current flow to a component?

I'm building a hexapod robot using simple servos and I was wondering how feasible it was to measure the current flow to each servo (5-6V DC to a maximum of 0.25-1A (I haven't found the spec for the ...
Len Holgate's user avatar
  • 1,078
9 votes
5 answers
2k views

Circuit that measures the speed of sound in concrete

I need a circuit to measure the speed of sound in concrete to 1μs or better. This is for a school demonstration where students who study construction will use this circuit to measure the speed of ...
FlaSh's user avatar
  • 261
9 votes
7 answers
20k views

Measuring 0 - 1MHz ( 0.25Hz resolution) Squarewave using an MCU

I need to measure the frequency of square-wave that can vary between 0 and 1MHz, and has a resolution of 0.25Hz. I havent decided on which controller yet but It will most likely be one of the 20pin ...
volting's user avatar
  • 897
9 votes
2 answers
53k views

What color is positive on a multimeter?

I bought a multimeter with attached leads. I would think red is positive but when I take a reading it only works if I use black as positive. Was it assembled wrong? There's nothing in the manual. It's ...
Jeffsbach's user avatar
9 votes
8 answers
1k views

Measuring the activation time of a solenoid

I'm trying to measure the activation time of a pull-type solenoid. When the solenoid doesn't have a load connected to it, you can measure its activation time through the current it consumes. At first,...
Florian Humblot's user avatar
9 votes
4 answers
396 views

How are high-speed circuits tested if test equipment doesnt exist?

How was testing done for Ghz to THz range circuits and devices before fast enough scopes and frequency counters existed?
FourierFlux's user avatar
9 votes
3 answers
420 views

Measuring force developed by a robot

I've been playing around with a Lego Mindstorms NXT robot, gearing it for speed and power. To my dismay, when geared for power, it wasn't any harder to stop than when geared for speed -- I suspect ...
Clinton Blackmore's user avatar
9 votes
2 answers
4k views

Can continuity test cause component damage?

In order to test some tracks on a mounted PCB, I would like to use a multimeter for continuity test. However, then I measured the open-circuit voltage of two multimeters at hand, and the results were:...
EquipDev's user avatar
  • 579
9 votes
1 answer
340 views

Why does the measured capacitance value of some ceramic capacitors keeps on increasing?

The capacitance of two ceramic capacitors were measured using an LCR meter (Agilent E4980A) at 1 kHz. The measured capacitance values of 100 pF and 100 nF capacitors are shown below. The value of 100 ...
arjun.ar's user avatar
9 votes
2 answers
5k views

How to use SCPI on HP33120A via RS232?

I have old Hewlet Packard 33120A function generator (it should be the same type as Agilent 33120A) and I would like to control it with MCU (ATMega). The generator has RS232 and use SCPI commands. I ...
vasco's user avatar
  • 957
9 votes
3 answers
7k views

How to measure the quality of a USB charging cable?

I have a set of USB cables (data and charge) and I noticed that, for a given charger, the charge time differs by cable. What would be a good way to measure the charging fitness of a USB cable? ...
WoJ's user avatar
  • 527
8 votes
5 answers
2k views

Word or phrase to describe how frequently a value is measured

When writing software for instrumentation, it is often required to specify a small gap of time between taking measurements. Say for example that 250 voltage measurements must be taken, and they must ...
Snoop's user avatar
  • 601
8 votes
6 answers
4k views

Are there any tricks for measuring high voltages (~1000 V) efficiently?

The simple way to measure voltages above VDD is to use a resistor divider. However, once you get into the 100s of volts these dissipate significant power. For example, one of my current designs ...
Drew's user avatar
  • 7,119
8 votes
5 answers
4k views

Does it make sense to measure components in-circuit in order to prove non-functioning?

When an electrical circuit is not working properly does it make sense to use a multimeter to measure/test the individual components in-circuit (without soldering them out), e.g. measure transistor ...
MRalwasser's user avatar
8 votes
4 answers
2k views

Measuring cpu load of interrupt routine

I have an isr that is updating a display at a fixed frequency. I would like to tune my routine to minimize overhead and keep as much cpu time as possible open for other processing, but I don't have ...
captncraig's user avatar
  • 2,054
8 votes
3 answers
4k views

Measuring resistance of a capacitor - unexpected results

I'm trying to measure the impedance (\$R_x\$) of C1 in the RC circuit shown below, but I'm getting some results I can't explain. simulate this circuit – Schematic created using CircuitLab ...
Alex's user avatar
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