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Questions tagged [instrumentation-amplifier]

An instrumentation amplifier (InAmp) is an integrated circuit or operational amplifier topology that has high input impedance differential inputs and a low impedance single-sided output. Because of precision laser-trimming techniques for passive circuit elements, InAmps implemented as integrated circuits can achieve impressive common mode rejection ratios, while discrete OpAmp implementations can be disappointing in this regard.

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AD8232/AD8233 not working for sEMG

I am working on an sEMG circuit using the AD8232 and cannot figure out what is going wrong, the circuit isn't outputting the correct signal when connected to the forearm. I am using the 3 lead ...
user2608683's user avatar
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4 answers
97 views

Instrumentation amplifier input bias currents direction and error

I am trying to understand how the input bias currents flow in op amp and instrumentation amplifier circuits and what errors they create. I came across a circuit that looks like the following: ...
Robert's user avatar
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Wiring of INA128 instrumentation amplifier to Wheatstone bridge

Is there any issue with the wiring or calculations of my INA128 instrumentation amplifier to my load cell Wheatstone bridge? Currently I see no change in the output when connected to the oscilloscope. ...
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Removing DC offset from AD8220 output (Instrumentation Amplifier) in electromagnetic application

I'm using AD8220 to amplifying a very tiny signal, which is made by a electrode in a electromagnetic flow meter. In the voltage that is made by the electrode there is an DC offset, then this DC offset ...
Andromeda's user avatar
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2 answers
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Instrumentation amp output not matching voltage drop in LTspice

I am trying to sample the voltage drop across different components at high frequencies, and figured the best way to do it was with an instrumentation amp so there's not much additional load placed on ...
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What voltage comes from a standard 6.3 mm instrument cable?

I am designing an electric percussion instrument using various metal strings and objects that are hit my solenoids. Pickups record the sound.I need to know what kind of voltage and current instrument ...
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Power supply issue with virtual ground for the INA333 and AD630 amplifier

I implemented a circuit with the INA333 amplifier to read a sensor, then the amplifier sends the signal to the AD630, which plays the role of a lock in amplifier, as in the diagram I sent. I made a ...
Lilian Pereira's user avatar
2 votes
1 answer
153 views

INA125 Reference Voltage lower than expected

I am using a INA125 to amplify the signal from a load cell. When I connect everything according to the datasheet as seen below, the reference voltage drops when I connect the load cell. I am supplying ...
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high voltage moderate frequency galvanically isolated current measurement

Given a conductor carrying a sawtooth wave of anywhere between 0.1Hz and 855kHz up to +-1.5kV) and anywhere between +-(1µA...20A)(maximum 650W) i want to measure the current with about 5MS/s (so the ...
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Noises from Sequential Bipolar Montage

If Fp1 and F3 forms a differential V+, V- and F3 and C3 forms another differential V+, V- and C3 and P3 forms another differential V+, and V- and P3 and O1 forms another differential V+, and V- What ...
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Noises when unused inputs not shorted with common V-

Update. Manufacturer confirmed all the 4 red V+ inputs used same blue V- and ground. Now what would be the noises introduced if only channel 1 is used and the 3 other inputs are floating (all ...
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What is the purpose of the "REF" pin of LTC6915?

I am working with a LTC6915 and i don't understand what REF pin does. That like V+ - V- + Vref = Vout? Or something else? I don't understand the datasheet.
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How to share a single gain resistor among multiple op-amps in a circuit

I'm currently designing a circuit where I need to implement multiple op-amps, each configured with the same variable gain resistor using a single digital potentiometer. To simplify the design and ...
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Noises are measured over a bandwidth. Is 50Hz and 900Hz noise the same at 1kHz bandwidth? [closed]

They say noise is over a bandwidth. At a bandwidth of 1000Hz. Is the noise at 50Hz and 900Hz similar? If yes. Please made a quick drawing how the noise at 50Hz and 900Hz look like roughly so I can ...
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Single supply positive-only signal amplification using INA126 (two op-amp in-amp)

I need to amplify a 0.15-0.8 V very low frequency signal to the 0-10 V range of an ADC. I'm having a hard time figuring out why an INA126 does work as expected with dual supply but seems not to work ...
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Level-Shifting not working in Instrumentation Amplifier

I want to shift the measured EMG input signal to the positive side to use ADC. I used the REF input of AD8421 to add an offset of 2.5V. I simulated the circuit below from the AD8421 datasheet on ...
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Unexpected signal at AD620 module output when Vsupply is on

I bought an AD620 instrumentation amplifier module and below is the module schematic. Souurce - https://protosupplies.com/product/ad620-instrumentation-amplifier-module/ A problem shows up when I'm ...
Jack Huang's user avatar
1 vote
1 answer
60 views

Recommendation for type of switch [closed]

What type of switch would you recommend for the diagram below?
fluggy 55's user avatar
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Input impedance of instrumentation amplifier

I have a problem understanding which resistors set input impedance of an instrumentation amplifier. What is the input impedance of the circuit given and what is the purpose of R250 (10k to GND)?
cubix's user avatar
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Choosing a supply voltage for an instrumentation amplifier

I am using a Wheatstone bridge to measure a resistance and an instrumentation amplifier to amplify the signal. Specifically, I am using the INA121. According to the amplifier datasheet, the input ...
user386164's user avatar
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Instrumentation amplifier using folded cascode op-amp is not working

I made the sizing for a folded cascode operational amplifier, which is working well, however when I am trying to implement an instrumentation amplifier in LTspice using the blocks, it does not amplify ...
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Do we have to share the ground between a load and a sense-resistor based current meter?

I see in the datasheets of some current-meter chips, that the LOAD ground is also the same as current-meter chip (inAMP for example) ground. For example AD8293 inAMP: Or this model (INA3221) from ti: ...
Tirdad Sadri Nejad's user avatar
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LT1970 output changes when I probe the voltage

I'm using an LT1970 for current control. I read the current with a shunt resistor and an AD8421. When I connected the circuit to a 10 Ω load, the AD8421 read 134 mA, but when I tried to measure the ...
SASKEEEEH's user avatar
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INA828 monitoring current shunt charging and discharging question

I am designing a battery current shunt monitor that measures current while discharging and also charging. I am planning on using the INA828 amplifier feeding an ADC. My questions revolve around the ...
Barry Jensen's user avatar
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199 views

Instrumentation Amplifier improper frequency response

Followup to this question. I have an instrumentation amplifier. When conducting an AC Sweep, this is the response. There are two issues with this. Firstly, the signal magnitude is far too low. ...
HFOrangefish's user avatar
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3 answers
102 views

Common mode voltage with configurations of Opamp

I am reading this article (https://www.analog.com/media/en/training-seminars/design-handbooks/designers-guide-instrument-amps-complete.pdf) in order to understand more how traditional instrumentation ...
TSLee's user avatar
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1 answer
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Input common-mode range vs output voltage (INA826) interpretation

I'm starting a new design using INA826 and analyzing the input common mode limitation, I do not understand the differences between this curves; I mean, why in figures 11 and 12, gain and VS is not ...
Facundo Piñero's user avatar
4 votes
1 answer
115 views

INA114 vs INA826: why is the INA114 so expensive?

I have been using the INA114 in my design, but wondering if I can use the INA826 instead. I cannot figure out what the difference between these two instrumentation amplifiers is. The CMRR is nearly ...
Dillon Stewart's user avatar
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1 answer
85 views

Are these switches really necessary?

I'm analyzing the OpenBCI Ganglion board and I reasoned that switches SW1 through SW4 (part number CJS1200) might in fact be useless. The negative input for each channel (X_IN-) is connected via a ...
AlexanderCar's user avatar
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No output when testing the AD620 amplifier with a function generator

I have a problem testing the AD620 amplifier using a function generator. I'm injecting a 100 mV sinusoid, and with the gain of a 1k resistor. In this configuration I would have a 5 V signal at the ...
Lilian Pereira's user avatar
2 votes
5 answers
158 views

Asking advice for designing an analog circuit with amplifiers

This is my first time trying to create a circuit by myself. I have been learning different combinations of circuits such as a differential amplifier, some kind of basic circuits with an operational ...
TSLee's user avatar
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3 votes
1 answer
298 views

INA128: EMG signal output voltage shift when leg touch the ground

I followed this circuit to get the EMG signals (dual supply +-9 V). I set the Rg at 330 Ω (at 2.8 kΩ, I can't see any changes in the output, so i set the gain higher), and replaced OPA2131 with TL072 ...
MonhVuv Vu's user avatar
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2 answers
110 views

Advice on Designing a Low-Current Photodiode to Digital Pulse Circuit

I'm currently working on a project that involves converting very low photo diode current pulses, typically around 100nA, into digital pulses. The pulse-repetition frequency (PRF) is about 10 kHz, with ...
kakeh's user avatar
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1 answer
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Non-constant active filter gain

I designed an amplifier using an instrumentation amplifier and an operational amplifier. Here, I used a 2 Hz high pass and 100 Hz multi feedback low pass filter, but I could not get the efficiency I ...
atıf koçak's user avatar
1 vote
1 answer
86 views

ad8426 instrumental amplifier design

I'm having a problem with my AD8426 instrumental amplifier design. As I show in the image, I use a 3.3 V supply and after increasing my input signal, I use 1.8V virtual ground to make it oscillate on ...
atıf koçak's user avatar
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0 answers
88 views

How to interpret input common-mode voltage vs output voltage in INA823 Datasheet

First, a similar question was asked before Understanding common mode vs output voltage graph for instrumentation amps, however, I failed to understand it with regards to my use case and need more ...
tronhawk's user avatar
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71 views

Challenges in measuring the output voltage of an H-bridge using an instrumentation amp and resistive divider

Design a circuit that allows me to measure the output voltage of a full H-bridge. Essentially, I'm using a resistive divider for this purpose. The simplified design is as follows: I had issues with ...
WalterPH's user avatar
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1 answer
100 views

50 Hz noise on INA125 for Wheatstone bridge application

I am trying to measure mechanical deformations using a full Wheatstone Bridge. In order to do that, I connected the bridge to an instrumental amplifier (INA125PA). The amplifier is powered with a dual ...
Benjamin SCHMIDT's user avatar
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1 answer
170 views

Output voltage thermocouple amplifier decrease when temperature increase

To detect surface temperature of heating foil, I decided to use thermocouple of type K. To amplify the small signal I choose the thermocouple amplifier with cold junction compensation integrated, ...
stefyanna's user avatar
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4 answers
1k views

Wheatstone Bridge with Instrumentation Amplifier

I have set up this circuit: I measure an output of 0.61 V from the instrumentation amplifier. The gain of the amplifier is set to 21. The formula for the output is given by: Uout=(1+2R1/Rg)×(R3/R2)×(...
Eirik's user avatar
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1 vote
2 answers
106 views

Multiple 4-20mA Transmitters from Common Referenced Analogue Inputs

I'm trying to come up with a scheme for multiple loop powered 4-20mA transmitters controlled from seperate analogue voltages, which all have a common 0V reference. My inital thought was to use an ...
Dan Twining's user avatar
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0 answers
69 views

The output of my instrumentation amplifier (INA121) is not seen in the microcontroller (MSP430)

I am using an INA121 instrumentation amplifier, and its output is 156 mV, but it is not seen in the microcontroller, it is just giving 0 like: I increased its output voltage (gain) by decreasing the ...
Merve Özdaş's user avatar
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1 answer
204 views

INA333 strange output, it's the same w/ and w/o input

This is the EOG (Electroencephalography circuit I'm working with) The output is essentially noise when I hook up the electrodes to myself, hence I'm debugging each stage, hooking up to an ...
roaibrain's user avatar
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1 answer
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12 lead ECG electrode configuration in circuit

I have one little misunderstanding about this diagram, how are the 9 ECG electrodes attached to INAs input legs, as there are even number of them (respectively 10)? Additionally, I'm not sure where ...
Nika Abashidze's user avatar
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1 answer
260 views

Voltage reference vs voltage bias for EOG circuit

This is continuation of my previous question. I'm confused about the reference voltage and bias voltage. As seen in the image above, the supplies for the INA333 and OPA2335 are clearly 3.3V and ground....
roaibrain's user avatar
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1 answer
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Why does this instrumentation amplifier (INA110KUG) output 9.8 volts even when input voltage is 0V? What am I doing wrong?

I've tried removing the resistors from the upper side but there was no change in output voltage. Datasheet:https://www.ti.com/lit/ds/symlink/ina110.pdf
Andrei Grigore's user avatar
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1 answer
75 views

Instrumental amplifier outputs in 12 lead ECG [closed]

Currently we are trying to build 12 lead ECG circuit, so we just need to know the answers to couple of questions. Why do instrumental amplifiers on given circuit have two outputs? How are they ...
Nika Abashidze's user avatar
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1 answer
75 views

How to design gain based on input voltage and ADC voltage range?

What are the parameters to consider when designing gain amplification whether it be 2- or 1-stage (why one or the other?) when given an input and an ADC? I see for the same kind of signal (biosignal) ...
roaibrain's user avatar
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Why is does my INA121 instrumentation amplifier not amplify my load cell's signal at high loads?

I am applying a high load (150-200lbf) to a (mV Wheatstone bridge) load cell rated for 200lbf (link to datasheets at bottom), and amplifying the differential signal with the INA121 instrumentation ...
Eric's user avatar
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1 vote
2 answers
72 views

How to understand the noise specifications of amplifier?

LT6370 Instrumentation amplifier has specifications as below. How should I understand this specification? Why only 0.1 to 10 Hz is specified, why not high frequency values? Thanks in advance.
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