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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15 views

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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80 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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41 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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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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19 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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37 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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50 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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38 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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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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73 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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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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65 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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90 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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74 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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45 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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48 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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81 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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87 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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57 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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80 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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185 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
502 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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46 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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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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37 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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67 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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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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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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111 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
117 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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47 views

Self Oscillating INA with Multiple Feedback filter

I'm working on a circuit to receive a signal in the 220Hz range. The signal is created from a small loop transmitter emitting a 50% duty cycle DC square wave of about 4.8 Watts. The receiver is a ...
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39 views

INA125 problems

I'm trying to measure a bridge sensor using an INA125 connected to my Arduino and Adafruit ads1115, but the output seems stuck on 5.88V (the power supply is 12V singl supply). Its connected as in the ...
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72 views

Operational Amplifier and Strain Gauge

My laboratory involves using a strain gauge and an instrumentation amplifier to amplify the signal from the strain gauge. The op amp schematic is shown below: Any assistance with the following ...
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1answer
35 views

XADC Current Sensing Reference Design

Please refer to this reference design for AC701 (snippet below). The schematics, specifically the current sensing sections in pages 34-36, show this: I want to understand why, for the REF output of ...
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42 views

INA125 gain problems

I'm trying to use an INA125 to read a load cell. Its connected as in the single supply diagram in the datasheet (see below). The gain should be 4+60K/Rg. However whatever resistance I make Rg, the ...
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41 views

Thermocouple chip & CJC compensation under 0°C

We are currently designing a "conditioning" module that takes a couple of sensors (T°, Pressure but also via digital bus) and repeats over CAN / also outputs them in nice and clean analog signals (0-...
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375 views

K-Type Thermocouple, Instrumentation Op-Amp and Arduino

I am Trying to read in a K-Type Thermocouple to a 0-5V Arduino Uno. I Can read my Thermocouple directly using a Fluke meter on temperature setting giving me the correct value of 21°C, but when I ...
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748 views

Not understanding how the gain works in the 1st stage of an instrumentation amplifier

For the following instrumentation amplifier, I am having some confusion understanding the gain process for the 1st stage. I understand that the 2 input amps are essentially 2 non-inverting amplifiers ...
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253 views

Why is a Instrumentation Amplifier Necessary for A Wheatstone Bridge (small signal circuits)

I do not understand why an Instrumentation Amplifier is Necessary for small differential signals? Why is it necessary that the initial inputs to the amplifier must be high impedance from the ...
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155 views

Why is an Instrumentation Amplifier Used Over a Standard Differential Amplifier? [duplicate]

I am having a bit of a hard time understanding why instrumentation amps are used over a single differential amp? For example, the differential signal that I have is very small and comes from a ...
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95 views

instrumentation amplifier with [2 opamp + ADC] vs [3 opamp + ADC]

I have an 16bit ADC able to do differential measurement with range -5V to +5V (ADS1115), do you think both circuits would work? It's required that the adc input is within -5V and +5V range, else it ...
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76 views

Why choose to tie the output to the non-inverting input of an op-amp?

I came across this schematic design of a driven-leg circuit, designed in order to enhance the performance of an ECG amplifier. As far as i can see, the solution provided here is a little bit ...
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84 views

Op-amp output wanders over the course of a few seconds

In one of our designs we are doing signal conditioning of a load cell (Wheatstone bridge) We have an issue where the main instrumentation amplifier an AD8224 has an output signal that wanders by ...
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380 views

Working of INA826 instrumentation amplifier for Pt100 RTD

The schematic below contains an INA826 used to amplify the resistance of the Pt100 RTD across J1. Gain is set to 10 through the 5.49K ohm resistor. Is this ciruit amplifying only the voltage across ...
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221 views

Can I use a simple voltage divider with an instrumentation amplifier to measure from 0 to 10V?

There is a design of a circuit proposed in the following way: simulate this circuit – Schematic created using CircuitLab The amplifier has a gain of 80, on R1 when the input voltage is equal ...
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122 views

Cascading Op Amps for Phototransistor Output Conditioning

I am working on a project in which I am using an IR phototransistor to detect changing low levels of light. Currently with very high load resistance I can get a reading of 40-60 mV but I would like to ...

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