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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24
votes
13answers
6k views

Level of a water tank with a microcontroller

How do i measure the level of a water tank with a microcontroller?
23
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5answers
3k 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 ...
19
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4answers
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 ...
16
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12answers
32k 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 ...
16
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3answers
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 ...
15
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3answers
2k 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?
14
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7answers
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 ...
14
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3answers
1k 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 ...
14
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3answers
2k 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 ...
13
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5answers
74k 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 ...
13
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4answers
41k 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 ...
12
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2answers
12k 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 ...
12
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2answers
3k 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 ...
12
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2answers
3k 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 ...
12
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2answers
891 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 ...
11
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3answers
10k 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 ...
11
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6answers
3k 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 ...
11
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3answers
2k 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 ...
11
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7answers
5k 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 ...
11
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1answer
10k 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.
11
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4answers
12k 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 ...
11
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1answer
3k 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 ...
10
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6answers
17k views

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

I am just wondering 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 ...
10
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2answers
2k 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 ...
9
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4answers
3k 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 ...
9
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3answers
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 ...
9
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4answers
290 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?
9
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2answers
4k 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 ...
8
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5answers
1k 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 ...
8
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5answers
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 ...
8
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5answers
3k 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 ...
8
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3answers
1k 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 ...
8
votes
7answers
18k 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 ...
8
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2answers
31k 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 ...
8
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3answers
2k 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 ...
8
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5answers
6k views

Water level detection, where water is somewhat polluted and has significant dissolved salts

Found this excellent QnA here which provides several options for measuring or detection water-level. For my case, it is enough to differentiate 4 levels of water (very low, low, middle, full), of the ...
8
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3answers
1k views

Will this approach accurately measure capacitance and infer spacing?

I am interested in any feedback or caveats regarding the following capacitance measurement method before I begin setting it up. For an experiment, I have come across the need to measure and track the ...
8
votes
3answers
356 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 ...
8
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2answers
3k views

Connecting phototransistors or photodiodes in series

I am designing a velocity measuring device and want to use 2 strings of 30 photo-transistors in series. The strings are 15mm apart and are illuminated by separate collimated light sources. The ...
8
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2answers
1k views

Does it ever make sense to use a 50Ω input with 10X scope probe?

I'm at the point in my learning where one discovers measurement setup for a scope at RF frequencies is quite a bit more involved than I thought :) I see the importance of thinking about the probe + ...
7
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6answers
2k views

how do energy consumption (Ah, kWh) meters work?

How do devices which measure energy consumed work? For example the ones in solar regulators/chargers which display how many Ah went into the battery and how many went out? Do they just measure the ...
7
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1answer
2k views

How to set the oscilloscope to measure potential between two points that aren't ground?

We have to measure the voltage across a-b in this circuit with an analog oscilloscope, but neither of these points are grounded. How should we put the channels of oscilloscope to perform the ...
7
votes
4answers
46k views

Can't get a precise reading with PT100 temperature sensor

I am trying to get more precise temperature value from PT100 ( 2 wire ) sensor with Arduino. Here's how my circuit looks like : When the sensor is about 20 °C I get a value on A5 pin that is 432 and ...
7
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2answers
3k views

How is a 50Ω “back-termination” accomplished on a scope probe line?

I've just been watching Jim Williams' very excellent video on Measuring Switching Regulator Noise. At 1:58 Jim mentions a "50Ω back termination" in the probe setup that looks something like this (but ...
7
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2answers
17k views

What does pitch means in the context of the sizing of a breadboard?

I am trying to build an eagle-cad part for an Arduino Micro. (so I can make a PCB and stick the arduino on it) I was hoping to derive the distance between the two rails of pins from the fact that on a ...
7
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5answers
4k views

Predicting thermal equilibrium: what's wrong with my time constant?

I understand that this is arguably a peripheral electronics problem, but it seemed to fit here better than in physics. I've been doing some power electronics design work with large IGBTs mounted on ...
7
votes
1answer
622 views

What does sequences like 1-3, 1-10, 1-3-10 etc in a spectrum analyzer mean?

I have read in a paper explaining spectrum analyzer basic 'When selecting the RBW(resolution BW), there is usually a 1-10 or a 1-3-10 sequence of RBWs available. More RBWs are better because this ...
7
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2answers
3k 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? ...
7
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2answers
543 views

real time short distance range finder and visual output

I'm badly visually impared in one eye and find judging distances while walking downhill hard. My goal is to create a real time range finder than can display the distance of the next step(s) while at ...
6
votes
4answers
9k views

Precise Resistance Measurement Techniques

This question is inspired by some basic questions on resistors I've read here lately. What's the most accurate/precise technique for measuring the value of a resistor you can think of? What level of ...