Measurements of the current flowing through a circuit

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Analog output using a current-output DAC and resistors

Does it make sense to have a 4-20mA output DAC and use a precision (~1%) load resistor to convert this to a voltage output with the goal of having a selectable current/voltage analog output? For ...
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2answers
132 views

What's the best MOSFET for switching small currents?

What are the most important characteristics to look for in a MOSFET for switch a precision 50nA load? The MOSFET should be able to switch the load on or off within 1us. The overshoot/undershoot ...
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2answers
53 views

Transistor for 4-20 mA voltage drop resistor connection?

This is for converting a 4-20 mA current loop signal to a voltage. Is it okay to connect the resistor for measuring voltage drop with a transistor to allow for switching between voltage and current ...
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3answers
144 views

Working out mAh from current and time

If I know how many millamps I'm drawing, and also for how many milliseconds, how do I calculate this to mAh consumed?
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2answers
91 views

What will be the value of Vo

simulate this circuit – Schematic created using CircuitLab This ckt comes as a question in our previous year exam. what will be current " I " and voltage drop " Vo " . It'll be very ...
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1answer
83 views

How to measure car battery current precisely in wide range (starter current, charging)

I want to measure car battery currents in high resolution and in wide range and both directions (including engine start and charging currents). I don't need very high precision measurement, but I ...
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2answers
74 views

Stepper current measurement puzzle

The basic puzzle: how to conveniently view stepper motor current on a scope? Edit 2014-04-14: More-sophisticated schematic and description. I am building a test fixture to examine the behavior and ...
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1answer
37 views

Measuring smartphone's battery State-of-Charge during charging

I'm designing a mobile device that uses a Li-Ion battery. It is required to indicate to the user the State-of-Charge of the battery, similar to how it's done in smartphones. At first I considered ...
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1answer
70 views

Circuit to provide 0-5 V output proportional to 0-30 A from C.T?

I want to design a circuit to protect oveload current of 30A.I have a controller board(PLC) which accepts the voltage range of 0-5 as an input and C.T with 1:7000 turns which can maesure 0.5 -60 ...
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52 views

High-current monitoring circuit

I have the following circuitry: Battery Supply => Current Monitoring Circuitry => DC Motors Battery Supply: 4AA NiMH batteries - 4*1.2V (1.5mAh * 4) Current Monitoring Circuitry: Max 4378 chip ...
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1answer
58 views

Max output current per I/O pins from Basys2 (SPARTAN 3E) board [closed]

I am trying to drive IR leds out of spartan 3E fpga on xilinx's BASYS2 board. I will be using external current amplifier to drive the IR lEDs with control singal from the FPGA. I need to know the max ...
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3answers
70 views

Voltage dip on MOSFET switchable current shunt

I have the following circuit built up in LTSpice which will be used to switch in different sense resistors for current measurements. The mAEn signal switches the M1 transistor on at t=10ms which ...
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1answer
84 views

Current Transformer giving a reading when not clamped around a wire

A split core current transformers is currently clamped around a live wire. One end of the transformer's output wires are connected to the analog pin of an Arduino and the other end has a 2.5V bias ...
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42 views

Galvanic Voltage and Current strength

This is a mouthful! I have a copper pipe fixed with zink coated (galvanised) saddles. I want to ascertain what the voltage would be in the dissimilar metal galvanic reaction between zinc and copper? ...
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1answer
48 views

What determines the frequency range of a current transformer?

Per the title, what physical or construction parameters determine the frequency range of a current transformer? I happen to be looking at these two from mouser, but I'm sure the question is generic ...
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2answers
125 views

How to sense current being used by motors

I have an Arduino project that provides 12v power to run motors, etc... I want to be able to measure the current (amps) that the motors are using (0 to 500ma). 12v comes from a battery, but that ...
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2answers
261 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 ...
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3answers
118 views

Using built-in gain on ADC vs different current-transformer?

I'm looking to eventually build an energy monitoring circuit using a raspberryPi as the controller and some type of ADC as the collector. I'm generally following the architecture of the emonTx used ...
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1answer
79 views

How to measure the PWM current with a DMM

I have a Fluke 87V, which is a True-RMS DMM, and I would like to measure the current in my circuit. I have 2 motors being driven by a PWM so I wonder if the DC current or the AC current measurement of ...
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1answer
73 views

burden resistor and/or voltage divider in an energy-sensing CT setup

I want to (eventually) build myself a home power monitor using basic current transformers. While reading on various circuit designs, I've stumbled upon what must be a very basic question. If we look ...
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2answers
212 views

Why don't hall effect current sensors exist for low currents?

There do not seem to be hall effect current senors available for small currents, say on the order of 500mA. I'm guessing this is due to some technical or physical limitation. What is it?
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90 views

Isolation in Resistive Current Sensor

In resistive current sensor, can it have two different supplies for the voltage divider circuit and the differential op-amp circuit? Since the op-amp only gets the voltage difference.
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4answers
110 views

Check if electrical current exists in high voltage

I'm thinking about a simple home automation project, containing a Rasberry Pi, a Sainsmart SPDT Relay, I would like to switch the state of a ordinary bulb (ON , OFF) using both the relay and the old ...
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3answers
283 views

Home Current Meter - is this a good solution?

I want to build a simple current meter to measure my power usage at home, and have the data sent to my blog's database. (I know there are similar solutions out there, but this project seems engaging ...
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2answers
50 views

Current measurement maximum time

On my multimeter I have two current measurement connection. One for the mA and one for the A. On the ampere one there's a time limitation but not on the mA one. Also they mention in the manual a kind ...
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1answer
151 views

Measuring the Current Draw from a LIPO Battery

I have been working with LIPO batteries to power my portable projects for a while (mostly in RC aircraft), but when using them, I have always had to guess as to how much charge is remaining. Now, I am ...
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1answer
87 views

Current Transformer - example (basic) circuit request

I'm trying to setup an XBee to monitor power usage of a device. At the moment, I'm trying to get a basic circuit setup on a breadboard, without the XBee. I have purchased a ...
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48 views

Choosing the correct transimpedance amplifier for my application

Intro: I am to convert current to voltage using a transimpedance amplifier. I have some specifications and I need to know what op. amp. parameters I have to worry about and approximate values of ...
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1answer
163 views

Measuring 230V AC current with low sample rate

I have a resistive load of order of 1kOhm, on a 230V AC circuit. The load's resistance varies a little over time - the current draw may float between some 0.2 - 0.25A, slowly (order of minutes). I ...
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2answers
75 views

Input current in an ic

I know that measuring amperage in a circuit, makes sense when you have load, but what if you have an ic component? I want to power supply operational amplifier LM741 ...
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2answers
131 views

How to measure current with multimeter

I want to measure both voltage and current from an output expansion port, of the BeagleBoard-xM. I managed to measure voltage by putting measuring lead (red) to the expansion port and reference lead ...
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2answers
93 views

Correct calculation of conductance/susceptane and from there to admittance, impedance, resistance and reactance.

I am sending a sine wave through a unknown RC circuit. At the other side I have a current-to-voltage converter (transimpedance amplifier) measuring the current indirectly as voltage. I am using IQ ...
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2answers
107 views

Accuracy when measuring current (mAmps) and small voltages

I'm looking at a circuit (part of a bigger circuit) that consist of a 10 ohm resistor and a red LED. It's running on 2.05V (checked with 2 different multimeters, ranging from from 2.047V to 2.05V). ...
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126 views

Battery measurement after charge

I got a Ni-Cd battery (8 AA) 9.6 V, 700mAh. After a 2 hours charge by an AC/DC adaptor (9.6 V, 250 mA) I take the following measurements by the multimeter: Voltage: 11.28 V (DC) Current: almost 10 A ...
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1answer
102 views

Clarify multimeter current reading range?

I'm a bit confused about the range on my multimeter. I have connected the multimeter to a 5V USB wall charger rated at 1.3A. When I'm measuring voltage, everything makes sense. It shows a 1 for 200m ...
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2answers
251 views

Checking for a short in a circuit with a large capacitor?

I'm developing a small testing application for my company that tests various hardware and software functionality. I do however have a problem developing a simple way to check for short circuits in ...
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2answers
165 views

Wide range current conversion transimpedance amplifier

I am struggling trying to think out a solution to design a transimpedance amplifier (TIA) which can convert 100 nA to 10 mA. This is 5 decades. I want to be able to amplify these to 1.5V minimum. (3V ...
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1answer
85 views

Digital potmeter in transimpedance amplifier feedback

I am considering using a digital potmeter with, e.g., I2C interface as the resistor in the feedback loop of my transimpedance amplifier. I am concerned about this. Will this add any additional noise ...
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1answer
270 views

PLC to act as or simulate 4-20 mA transducer

I have a PLC Control system that measures a few 4-20 mA pressure sensors. Today we test these with loop calibrators on each channel. I want to set up a PLC that simulates these pressure sensors so I ...
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2answers
282 views

Why does a multimeter put more voltage to measure a smaller resistance?

I noticed this behaviour on two different multimeters (different models and brands as well). At first I did not put a multimeter in the way to measure how much voltage changed for the different scales ...
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3answers
162 views

I'm looking for a low budget current sensors for AC

I'm looking for a low budget (< 10$ per sensor) sensor for measuring AC current up to 20 A. I found many current transformers but they go up to 5 or 10 A. Any idea what types would fit? ...
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1answer
261 views

Reading AC signal from a XBee analog input pin

I'm trying to use a ACS756SCA-100B - 100A Hall Effect-Based Linear Current Sensor IC (SCT-013-030) with a precision of 20 mV/A. My objective is to read input voltage coming from the sensor into the ...
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2answers
146 views

What is the minimum current a current transformer can sense?

Datasheet of AS-100 mentions a maximum current it can sense before saturation, but what is the minimum current it can sense. For instance, if I put 10 mA 50Hz through a conductor passing through the ...
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109 views

Calculating reflections

I just solved a problem in my homework. I had to calculate the reflection waves and I was given the following data: // Resistance R0 = 120 Ω line impedance Ri = 90 Ω resistance at input Rb = 1 ...
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94 views

Hall Effect Current Sensor IC Data Sheet

I'm feeling like an idiot here. I've found this great little IC that will do the job I want but I can't seem to figure out what the max voltage is that can be supplied for sensing. The IC runs on ...
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3answers
176 views

FPGA Power measurement

Are there any methods by which one could measure the current being drawn by an FPGA in real time i.e., when it is actually deployed in a working system? Where can I get some information about them?
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1answer
113 views

Split-Core Current Transformer - Disconnecting secondary load questions

I have heard that disconnecting the secondary load from a current transformer while the primary line is passing current causes a huge voltage spike (from a question about CTs that I can't find again). ...
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442 views

How to measure max current of a power supply

I have a 220V to 12V adapter. According to the adapter label, the max current can reach 1.5A. But I want to measure the max current it can reach without depending on the information written on the ...
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210 views

Current transformer as Sensor, can it sense rectified DC current?

I have been using an inductor around a 230V AC wire ground-side of the switch to check for current in a wire, it is part of control mechanism. I have to add a rectifier now, so occasionally the ...
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2answers
268 views

Low side Current sensor design

I need a suggestion on a good amplifier design for a current sensor. The requirement is: Operating voltage between 2.7 to 6.0V Able to output 3.3V when a 10A current is flowing through sensing ...