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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85 views

Trying to increase resolution of ADC using an op-amp

We currently have a circuit measuring a thermistor in a water tank, passing through a couple of voltage dividers and then plugging into an 12bit ADC which eventually interacts with a microcontroller ...
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29 views

Selecting between 60V source and 1uV measurement

My goal is to perturb a sample with a 250us pulse of 100mA at 60V, then on the same probes measure the response over time in microvolts. The pulses will be repeating at about 100Hz, so most of the ...
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59 views

Reverse polarity protection on AD623 inputs used to measure low voltages on a sense resistor

This circuit used to measure low voltages on a sense resistor is part of my current meter in arduino that measures currents from 0.005ma to 5A. I configure the gain of the instrumentation amplifier ...
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98 views

Instrumentation amp vs buffered difference amp

The topology often used within integrated inamp packages often look like this (where the gain is conveniently set by a single resistor): There is another topology that looks more like a buffered ...
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56 views

Suitable op-amp and voltage regulator for 16-bit ADC

I would like to use the AD4008 16-bit ADC from Analog Devices to sample a load cell. I also need a linear regulator and driver amplifier and instrumentation amplifier. I am curious to know if these ...
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35 views

How to measure the voltage over a transducer? aka how to measure ultrasound

I want to measure ultrasound. For this task I bought a sensor, and an instrumentation amplifier. Apparently it doesn't work the way I thought because when I test it with a sample 40 kHz wave as input ...
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75 views

How to calculate the current / power consumption of instrumentation amp with op amp as an impedance converter at REF input

I have a measuring bridge and want to connect it to an ADC with an AD8227 instrumentation amplifier (Datasheet). For the reference voltage, I have connected a voltage divider to an LP358 as an ...
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2answers
67 views

AD623-Unable to change gain or reference voltage

I have an air flow sensor (FS1012-1100NG) with expected differential output voltages ranging from -1mV to 20mV and I need to 1) know the precise value (mV) and gain to correlate V with airflow 2) make ...
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30 views

Instrumentation amplifier & microcontroller ADC protection circuit

I have a couple questions related to protecting my instrumentation amplifier and the ADC of my MCU. The circuit is as shown in the image, with the input to the in-amp (an AD8223) being a very weak ...
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44 views

Instrumentation Amplifier Gain set resistors

We are looking for Instrumentation Amplifiers for an application.  At this stage, we have decided a certain gain value for our Instrumentation Amplifier. The datasheet of the product mentions the very ...
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47 views

DC offset before signal being fed into an instrumentation amplifier from a bio potential source

I am trying to design an instrumentation amplifier, having 2 bio-potential sources as its differential inputs, each having peaks in the order of 10's of uV and a frequency band of 3-50 Hz. One of the ...
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79 views

One milliamp current source for RTD

I am trying to design a one milliamp current source (Howland current source) with a precision of +/- 1 uAmp. The current source will be used to measure temperature with a 3 wires RTD sensor (H-T-01-12-...
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Instrumentation amplifier didn't fix my ADC crosstalk, and I don't understand why

A previous iteration of my circuit was as follows: I am sensing DC voltages across 6 variable resistors (1kΩ Pt RTDs) The 6 resistors are connected in series; the series is connected to a current ...
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22 views

What is the best TVS/ESD protection for Wheatstone bridge circuit?

I have 150K ohm on three legs of Wheatstone bridge, one leg on human body (skin), bridge excitation voltage is 5V, differential amplifier is be used to read the differential voltage of the Wheatstone ...
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1answer
61 views

What does Vaa mean?

I'm trying to understand this circuit. It looks like all the NCP chips are just voltage regulators, but I don't understand the VDD and VAA labeling, what do these mean. Also, any idea why the top ...
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Is it possible to replace the ref pin of AD620A with a fixed voltage?

I am trying to implement the below circuit (from) without ADuC842, I will use Arduino mega2560 ADC. the circuit generates -5V to 5V rail to rail voltages for ad620a and they control ref voltage via ...
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Switched-cap/charge pump only way to generate negative rail voltage for op-amp?

I need to design a daughterboard that gets mounted directly to a piezo mic to condition the signal before transmission. Part of the conditioning is a full wave rectification. Thus, as you'd expect ...
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2answers
85 views

Amplification Circuit for Generating High-Current Sinusoidal Signal to Feed a Coil

I am trying to implement a control algorithm using Arduino Due. I need to generate high-current constant-frequency sinusoidal signals to feed a coil using some batteries. The coil will generate ...
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1answer
46 views

Resistors in an instrumentation amplifier

I'm designing a circuit where I'm using instrumentation amplifier to amplify my input voltage The formula for the amplifier is $$\frac{V_{\text{out}}}{V_{\text{in}}} = \left(1 + 2\frac{R_1}{R_{\text{...
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971 views

What does m% stand for?

What does m% mean? Like in this datasheet from TI at the gain error graphs: http://www.ti.com/lit/ds/symlink/ina149-ep.pdf?&ts=1589388038122 Is it supposed to mean per-cent-mille (10^-5) or per-...
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23 views

Bias Input Current Compensation for Instrumentation Amplifier

What is the motivation to choose R1=R5=5k6 Ohm? If they are for bias current compensation and both OP Amps have same Bias input current, 10k should be taken in my opinion to eliminate common mode ...
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38 views

Instrumentation amplifier dealing with wire resistances

Can anyone please help me in understanding the output of this amplifier? According to me it is coming as (E1-E2)(1+(Rw/R)). I am more curious about knowing wheather Rw will come in the output ...
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Evaluation of multiple Wheatstone bridges using one instrumentation amplifier

I need to measure 8 different strain gauges. I am thinking about using just one instrumentation amplifier to evaluate all Wheatstone bridges (because of the high price of instrumentation amplifiers.) ...
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1answer
56 views

Measuring current, instrumentation or differential amplifier?

I want to measure current at the high side of circuit with 0.1 mV accuracy using a 16 bit ADC. for sensing the voltage drop over a 100 mΩ 1% resistor I need to use an op amp which is cheap and easy to ...
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mV variations even with a simple voltage divider

edit: After using a prototype pcb instead of breadboard, placing all possible electromagnetic sources away and unplugging all the equipment from the same line, my noise dropped 2 orders of magnitude. ...
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1answer
39 views

Unable to get instrumentation amplifier to work correctly

I have built an instrumentation amplifier using an LM348N quad op amp, supplied with ±9V. A simulation of the circuit is done as in the link - Simulation: But when I connect the circuit accordingly, ...
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398 views

Is AD7794 a good alternative to Hx711 for multi-channel ADC?

note: Electronics isn't my main background so I might make silly mistakes. I did read the datasheet but don't understand all the terms despite my effort. Suggestions are welcome. AD7794 (datasheet) ...
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77 views

Instrumentation amplifier - schematic review

I'm trying to make an instrumentation amplifier to measure a sine wave signal of 0 - 1Vpp (max) 50Hz that comes from a non-invasive current sensor (30A SCT-013-030). It gives 1Vpp at 30A current. ...
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25 views

How can I add an offset voltage at the input of an instrumentation amp?

I want to measure the voltage of an H-Bridge Sensor. However, due to the manufacturing process, the bridge has an offset several times larger than the useful signal (it can easily measured by ...
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1answer
73 views

Advice on generating a negative supply rail (-5V) in an embedded, mixed signal design

I'm designing a board that can take an input DC supply of between +8 and +36V DC (+12V nominally) and needs rails of +5V, +3.3V, +2.5V and +1.8V. My current design uses a step-down regulator (LMR23625)...
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1answer
115 views

Instrumentation amplifier, discrete or integrated?

Since integrated instrumentation amplifiers are so readily available, does it still make sense to incorporate an instrumentation amp discretely built from multiple opamps and resistors? Would one see ...
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84 views

Why use difference amplifiers over instrumentation amplifiers?

I know that instrumentation amplifiers are difference amplifiers with buffered inputs, and I understand why one would select an instrumentation amplifier over a difference amplifier circuit. But is ...
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1answer
73 views

Differential RC filter

I sometimes see differential filters like this: And sometimes this : Basically sometimes there are 3 caps (2 going to ground on each input), sometimes I only see 1 cap ( 1 differential cap, none ...
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54 views

Use a precision opamps or instrumentation amplifier for load cell application

I'm making a low power weighing scale with good precision. I'm contemplating if it'll be better to build a instrumentation amplifier with discrete OPAMPs of LPV821 which is low power (Iq 650 nA), high ...
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21 views

Error Propagation and Analysis on a experiment due to Voltmeter Constraints

I got a situation: at the moment I am unable to access both channels for Keithley 2182A nanovoltmeter using LabVIEW. However, for some odd reason, while I cannot access the channels at once, LabVIEW ...
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41 views

How to handle disconnected resistive sensor?

I'm trying to connect a PT100 thermo probe to an Arduino project to measure water temperature. After some research I have found and adopted a design using a Wheatstone bridge and an instrumentation ...
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2answers
82 views

Instrumentattion amplifier gain appears to change

I made a very simple circuit to amplify a ~1 mV signal up to ~2 V. The input is a 0~2 mV DC signal from a scientific instrument. The problem: I made the circuit, and it worked as intended. The 1 ...
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2answers
91 views

How to design two circuits with Instrumentation Amplifier to produce the same output?

I want to measure the current in a 5V circuit. The current is between 50uA and 2.5mA. The current is from a NTC and it changes slowly (10Hz measurement is fast enough). Here is the typical ...
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1answer
64 views

AD620 reference terminal problem

I'm trying to add a DC offset level to a sine signal through an instrumentation amplifier (as the figure below shows.) The problem is that, in the simulation, everything works perfectly, however, in ...
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2answers
100 views

Hall Effect Shielding

The objective of the circuit below is to get the difference of the hall effect output and a 1 volt reference, then amplify it. When I first built the sensor and tested it, it worked very well. This is ...
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2answers
196 views

Instrumentation Amplifier - circuit analyze

I found this schematic in LT1014 datasheet: What the pointed op amp (and the circuitry around it) is for and how it works? Why do we need to cancel the bias current? What's the application for such a ...
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1answer
794 views

AD620 Instrumentation Amp EMG circuit [duplicate]

I was looking at the datasheet of AD620 instrumentation amplifier. It had a circuit for measurement of EMG signals. The gain of 7, as written on the amplifier, is justified for this amplifier ...
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47 views

Sampling Capacitor In INA

I am looking at parts like the LTC2053 which use a sampling capacitor on their input. I had a few questions: Does the input impedance of this amplifier simply look like the sampling capacitor (1000pF)...
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20 views

Higher gain at higher frequency in instrumental amplifiers

I am using an instrumentation amplifiers (INA181). When the gain (G) is set to 10000 the behavior is as expected. However, when G is set to 1k there is an increase in the output signal going with the ...
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1answer
39 views

Cascading two instrumentation amplifiers to achieve higher gain

Is it possible to cascade two instrumentation amplifiers (for instance INA128)? let's say each has a gain (G) of 100 up to 100 kHz. Would this result in a G=10k up to the same frequency?
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83 views

Calculate the differential common-mode gain of instrumentation amplifier

I am trying to design an instrumentation amplifier with a CMRR of 50 dB. I have to target a differential gain of 60 dB. $$ CMRR(dB) = 50 dB = 20log(\frac{A_{vd1}}{A_{cm1}})+ 20log(\frac{A_{vd2}}{A_{...
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27 views

why is the reference of strain gauge changed depending on gains of amp? use ina128 and ad8542

I made a circuit for a load cell. It is available but when it is applied to the strain gauge, it has a problem. Reference voltage : 1.65 V When I measured value of load cell, I can see the change ...
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1answer
42 views

Servo drive in biopotential amplifier

I have to design a bio potential measurement system: AD converter and the connecting digital / software part an analog amplifier stage: basically a regular ECG amplifier composed of discrete ...
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1answer
119 views

What actually is the differential gain of an operational amplifier and why does its value change when we consider the common-mode gain?

Okay, this may be a stupid question, but at the beginning of my Applied Electronics course they taught us that the differential gain \$A_d\$ of an operational amplifier is ideally infinite; however, ...
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1answer
177 views

C0G vs polypropylene capacitors in signal filtering

Can anybody give me a comprehensive pros and cons list or explanation about the differences between C0G (NP0) ceramic and polypropylene capacitors? I would like to use them in signal filtering and ...

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