# Questions tagged [measurement]

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

747 questions
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### Level of a water tank with a microcontroller

How do i measure the level of a water tank with a microcontroller?
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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.
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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?
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 + ...
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### 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 ...
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### 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 ...
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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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? ...