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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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Measure small capacitance value

I need to measure C value continuously over time, and save the value to some text file (csv for example). Note that C changes over time, since the system is dynamic. C are small, varies between 50 to ...
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35 views

Accuracy of small changes

Suppose I have a low-noise DC signal at 5.000 V, and that I can measure it to 0.1% accuracy and 10 uV precision. Then suppose that the signal makes a step increase of 1 mV, so that it now holds at 5....
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593 views

Battery current measurement with shunt resistor

I want to use a shunt resistor to measure the current that flows from and in a battery. The current is set by power supply for charging(positive current) and by electronic load for discharging (...
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391 views

AD620 doesn't amplify signal between 1-60mv

I want to amplify a differential voltage signal between 1-60mV usign AD620. But I don't understand why it doesn't work. If I remove Rg I must have gain=1, instead I have a gain smaller than 1. I ...
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81 views

Replacing Multimeters with Megaohmmeters

Standard Digital multimeters can measure up to the ranges of 20 Megaohms. Then why should we use Meggers at all?
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480 views

How do I measure the error of my ohmmeter

I have to do an Ohmimetro to a college assignment, but I don't know how discover the measure error of my circuit. When we buy a multimeter, the equipment has a measure error calculated by the ...
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29 views

Practical verification of equations

This question is reffering to MOSFET. If you calculate drain current with a specific formula you can also verify that same value with measurement. But if you calculate partial or overall gain, you ...
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2answers
328 views

Op-amp with constant gain for small signal(mV)

simulate this circuit – Schematic created using CircuitLab I want to measure current using shunt resistor and I want to amplify the voltage over the shunt using an op-amp. The shunt resistor ...
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35 views

current measurement in series-parallel solar panel array

I have a solar panel array wired in series-parallel. I know the voltages in a series network will be the average voltage, and the current in a parallel network will be the smallest contributing ...
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125 views

Measuring mains - shifting ground from mains to bridge

The circuit below is a simplified and partial front end schematic of a solution that measures main voltages and takes action if over voltage, under voltage or "wrong voltage" (e.g. user plugged into ...
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0answers
127 views

Why does inside of my sphere appear to be getting darker?

This a fully enclosed sphere containing a web cam, white led and photo resistor in exactly the geometric arrangement shown. The led glows dimly (via fixed dropper resistor). It runs at about 9 mA. ...
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1answer
154 views

Measuring electric current in shield

I have noticed that there is some current (not dangerous levels) in the shield around the power supply in my computer. Would it be safe to measure the current (Amps) going through the shield with a ...
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403 views

cheap sub uH inductance meter?

Can a cheap RTL-SDR (with suitable software) plus a variable frequency digital output (for noise or square wave generation) be used to construct an inductance meter suitable for measuring values in ...
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518 views

Measuring noise on DC rails with active probe

I have a Tektronix P6245 active probe (allows only DC input) and wish to use it to see noise on various power supply rails. I've done this already on a +3.3V rail, and can get sufficient DC offset on ...
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96 views

load cell number and accuracy

I want to measure weight, so I use load cells, As far I know, commonly 4 load cells are used for this purpose, but I can not understand it's real purpose, maybe 2 will be more accurate than 4? Is it ...
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181 views

Proper way to measure an AC signal with an oscilloscope

Is there a correct way to measure an AC source with an oscilloscope? As shown in the schematic below, I've got a current transducer that is expected to output an AC current of about +/- 1 mA (approx.)...
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158 views

Contact-less liquid level indicator [closed]

I am developing a Liquid level indicator to be used for my lab breaker. The purpose is to get real time liquid level data on computer for analysis. I have searched for many liquid detectors, but ...
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3answers
3k views

Precision Power Supply / Elektor, December, 1982

Since this PSU was published by Elektor I assume that some of you might heard or read about this project. http://www.retro.co.za/zs1ke/projects/PrecisionPowerSupply/PrecisionPSU-Elektor-Dec-1982.pdf ...
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745 views

ADC and internal noise

Hy everyone, I have a question regarding AD conversion in a microcontroller. Before we go on, I use a dsPIC33EP64GS506 (link on its datasheet), 3.3 V power supply, ...
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1answer
774 views

At what test frequency should electrolytic capacitors be measured?

At different frequencies electrolytic capacitors have different capacitance. Suppose it is 50 uF 16V capacitor (type K50-16), then the measurement results are (using russian E7-14 RCL tester): ...
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1answer
95 views

ACS712 cutting out

I'm using an ACS712 based current sensor board (Exact here: http://tinkersphere.com/sensors/1244-hall-effect-current-sensor-breakout-acs712.html) For testing purposes I have connected Vcc and GND ...
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145 views

S-Parameter measurement of a balanced device

I want to measure at least the differential S-parameter of a balanced device. Unfortunately the device is a black box, i have two differential leads going into the device and two coming out of it (no ...
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1answer
1k views

Any way to measure distance through water?

I have a barrel of clear liquid which has sediment build up at the bottom of a barrel. Over time I want to measure the build up of this sediment. Nothing can touch the liquid and I can't place ...
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206 views

\$V_{BE}\$ decreasing with \$V_{CE}\$ at constant \$I_B\$ in a BJT common emitter?

I took measurements on a TIP31 common emitter BJT transistor. The circuit was the one in picture I observed a fact which seems quite unusual. Keeping \$I_B\$ constant, for different values of \$V_{...
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3answers
718 views

Should a capacitor be considered functional if it's capacitance reading is correct?

There are many different ways to test capacitors. Using a capacitance meter, using a DMM and an analog meter. In general, is it safe to assume that a capacitor is considered functional if it's ...
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112 views

How to estimate displacement error using accelerometer

I am using an MPU6050 and performing a double integration to obtain displacement, and this is to be placed in a vehicle that will be subject to about 2.5g. I cannot test it now, but how is it possible ...
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1k views

What is “Vref” of ADC in a microcontroller datasheet?

I'm kind of lost in the datasheet of the µC. I'm using an XMC4700 µC. I will connect a voltage divider to the input of the ADC to measure the voltage. I found the equations to calculate the result. ...
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86 views

Can a capacitor have high series resistance and low Q and why?

I measured with an LRC meter (Agilent 1731A) a capacitor at frequency \$1kHz\$, finding \$C=109.4 n F\$. Then I tried to measure the resistance and quality factor of the capacitor: here is what I got....
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3k views

Measuring the resistance of a real inductor?

Real inductors can be represented as perfect inductor plus a series resistance \$R_s\$. The impedance of this component is \$Z_{L+R_s}=R_s+j \omega L\$ therefore $$\frac{1}{Z_{L+R_s}}=\frac{1}{R_p}-\...
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1answer
85 views

Measuring current and internal impedance of current source

I am building a current source for an EIT project that I am doing. I have not reached the multiplexer part as I am still having issues with my current source. I am developed the current source as ...
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3answers
598 views

Understanding “dBc” in the context of IM3

Let's say I'm doing a two-tone test to measure intermodulation distortion in an RF power amplifier. I look at my spectrum analyzer1, and I see this: The tops of those main lobes are at -105dB, and ...
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1answer
377 views

When is it necessary to connect all scope probes to GND (instead of just one)?

Oscilloscopes typically have multiple input channels which have a common ground (which also happens to be earth referenced). The problem is that the probes can be connected to ground through a huge ...
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814 views

Verifying supercapacitor capacity

I have procured some supercaps. No datasheet was provided. The only data I have is what is printed on the caps themselves: "4.0F 5.5V cda®" Since my DMMs don't ...
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MEMS or other modern component electroscopes

I was looking for a component-style electroscope. I thought, "Surely there must be some MEMS-based electroscopes capable of 2- or 3-significant-figure potential measurements." But the only thing ...
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1k views

How to calculate internal generator resistance?

What's the formula for calculating generators internal resistance in a circuit with a load? I am given the load resistance and the voltage sources voltage. What's next? simulate this circuit – ...
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How closed loop temperate control works in Ecigarette / Vaporisers

I have been reading about the use of heating elements made from Nickel and Stainless Steel in Ecigarettes. They are used as their resistance changes approximately linearly over the temperature range ...
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4answers
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Is measuring noise as V/√Hz obsolete?

I've been quantifying the peak to peak level of noise on a 24V Zener diode. The noise distribution is log normal, consistent with the literature regarding avalanche effect. The apparatus is:- ...
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1answer
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How can I find out a components voltage rating and amperage draw?

I bought a whole bunch of components for mounting on a circuit board (I'm new to electronics and I'm just experimenting at the moment) - things like LED's, small microphones, buzzers, very small ...
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micro ampere measurements [duplicate]

This question is very basic but I could not find it among previous questions so here it goes: I am trying to measure the current of a very low power device with very short intervals of activity. I ...
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2answers
681 views

Digital temperature meter probe wire length

I bought a cheap Chinese digital thermometer like this one with this description Link to product Item specifics ...
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4answers
1k views

What is the noise level as read on my oscilloscope?

The above is what I'm seeing on my oscilloscope. It's zener diode noise. Scope's set for 0.5V/div vertically, and 1ms/div horizontally. The oscilloscope has a 20MHz bandwidth, but the noise doesn't ...
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1answer
55 views

Calibrating EMC Setup at University

My university owns a Teseq NSG4070-35 conducted immunity measurement unit, including a 6dB attentuator and M3-CDN. In the handbook and datasheet of the device it says that the power meter is ...
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1answer
94 views

IR signal strengh measurement

I have an application where I have multiple IR transmitters/receivers set up to read data. These are removable and can be set up in a lab environment where I can control distance, light, etc. I've ...
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54 views

Capacitor tolerance at high frequencies

I was measuring a 10pF 0603 +-5% (Johanson 251R14S100JV4S) using a network analyzer at 319.5MHz. The cap came in their high q/low ESR ceramic kit. It measured about 10.7pF. But after measuring a few ...
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3answers
972 views

Measuring the impedance of a speaker

I want to measure the impedance of a speaker (by different frequencies). The idea to test it was the following, I have the follow circuit: Now, in order to find the impedance I measured the voltage ...
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1answer
656 views

Calculation and measurement of input and output impedances of a Class-D amplifier

How would I calculate, from datasheet information or elsewhere, the input and output impedances of a Class D power amplifier, in general or for say a chip like the LM4670 or the TPA2000D1? {Note that ...
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2answers
4k views

What's the difference between sensitivity and resolution of an SMU?

In Keithley's Low Level Measurements Handbook, 7th ed the two terms are defined as: SENSITIVITY - the smallest change in the signal that can be detected. RESOLUTION - the smallest portion of ...
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495 views

Sine wave pwm signal measurement with digital oscilloscope

I am beginner in electronics and I would like to measure 12 kHz sine wave pwm signal on the output pin of my microcontroller. My problem is that I am not able to setup the digital oscilloscope RIGOL ...
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1answer
364 views

Measuring loop Gain and phase of of a flyback converter

I have a flyback converter based of the LT3798. The converter takes a rectified AC (120Vac,60Hz) and steps it down to 24Vdc. It uses a third winding on the transformer to power the IC and to generate ...
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1answer
276 views

Measuring power factor of a single phase motor on a three-phase service

I am trying to measure the power factor of a single phase, 208V compressor motor that is connected across phases B & C of a three-phase service and drawing 8-10A. My first attempt using a Fluke ...