Measuring the output of strain gauges
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- Опубликовано: 30 сен 2024
- In this video I show you what are the challenges of measuring the tiny changes in the resistance of a strain gauge. The resistance of an unloaded strain gauge is around 350 Ohm (at least the one I use in this video) and a loaded one's is 1-2 Ohms smaller or larger. This is a small change, it is difficult to measure it and it is even more difficult when it is a change in the resistance of something. To make this value into a more comprehensive one, I use a Wheatstone bridge to convert the change in the resistance into a change in voltage. The obtained voltage change is still tiny (few tens of microvolts), therefore I use the built-in PGA (Programmable Gain Amplifier) of an ADS1256 AD converter to resolve this tiny change.
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where did you get the strain gauges?
Please kindly visit my website and check the "Parts and tools" page. It is at the bottom in the miscellaneous items group.
I have a basic understanding of this having done some electronics in night college. Maybe this is a dumb question as I don't know much about strain gauges. Is the voltage output linear? If put 1 ounce of weight on a strain gauge and see 1 mv will I see 2 mv if I put 2 ounces of weight on the strain gauge. I'm trying to picture how a digital scale uses a strain gauge. Thank you.
It is not a dumb question. Strain gauge gives a linear output which is proportional to the applied strain. The response (sensitivity) depends on the parameters, and these parameters are provided by the manufacturer of the strain gauge. The final response of the strain gauge depends on the bridge used and the signal amplifier as well. Basically, you have to design the circuit around the strain gauge/load cell to get a predefined response. The material of the load cell also can affect response as materials with higher Young's modulus will deflect less (smaller strain, see Hooke's law) than those with low (steel vs. aluminium).
Great video! I just ordered a kit online for 4x half-bridge strain gauges that can be connected with HX711 to Arduino. My question is, your video shows only 2 wires for each strain gauge. The kit shows 3 wires coming out of each strain gauge... is that because it contains 2 strain gauges in each sensor (one in compression and one in tension configuration) to double the output voltage difference?
Hi and thank you! I think the three-wire strain gauge is what you just correctly explained! Usually, it is called a half bridge strain gauge. As far as I know, the most straightforward application of this is the cancellation of the temperature effect. One strain gauge is exposed to the strain to be measured but the other is not, so it is a "dummy" strain gauge and the change in the temperature will change the Wheatstone bridge in such a way that the temperature-induced effects will be cancelled out. But please notice that the "3 wire strain gauge" can be achieved either by two similar strain gauges wired in a certain way, or you can buy strain gauges where there is a special pattern of wires on the resin sheet and the geometry of the wires will result in a 3 wire configuration.
Hi. Which is the kit? Thanks
Hi Curious Scientist,
I have been watching your videos over strain gauges and found them to be very educational. I am looking to do my own personal project similar to your video "Measuring the output of strain gauges." I plan on subscribing to the Bachelor of Curiosity very soon, but I just wanted to ask if the code for the "4-channel data logger" can be purchased through the Bachelor of Curiosity or donations.
Hi!
The software is not shared on my Patreon. In general, I only share Arduino software, and computer software are not public.
However, I will soon start selling a data logger software for PC, but that is separate for Patreon.
@@CuriousScientist hi. Are you selling the Dara logger now? Thanks
@@co.m.sigmasrl2213 Hi! No, I am not yet selling it. I will announce a video about it, so you'll definitely see it if you are a subscriber. Cheers!
Is there any limitation to the length of the leads going to the gauge? In my situation I would like to have somewhere between 6 to 9 feet. Would there be any problem with that? Thanks
Noise could be an issue, but if you use shielded cables, it should be fine. Most of the equipment I use at work are packed with strain gauges (load cells), and they work just fine, even with longer wires. But once again, shielding and probably twisted wires, too, are a must!
@@CuriousScientist Thanks for the reply, much appreciated!
It's my pleasure!
@@CuriousScientist I have another question if you don't mind. I recently set up a test circuit and noticed that the temperature of the strain gauge is effecting the voltage output. The warmer it gets the lower the voltage drops and the opposite happens when cooled. Is that normal or a sign of a cheap/faulty strain gauge? Thanks for any help.
The strain gauge is super sensitive, so what you see is the thermal expansion and also the temperature coefficient showing up in the measurement. This is why you need at least a half bridge, which can be used to cancel out the thermal effects. It is not the faulty strain gauge, it is the nature. 😎
can we get that strain gauge gui software
Hi! Yes, soon, it will be available for sale on my website.
Thanks for this.. seeing you work with a breadboard made me confident in not needing the strain gauge manufacturers ridiculously expensive amplifier for testing while making our own..
Hi! I am glad that you found my video helpful! As long as you are not looking for extreme precision and high resolution, you can work with relatively simple circuits. If you want to improve the things, you might want a stable voltage source for the Wheatstone bridge, a high-resolution AD converter (16 or 24 bit) and some amplifier. But in my opinion the built in PGA of the ADS1115 or the ADS1256 is enough for "hobby purposes". Part of the high price of the professional equipment is that they need to fulfill different standards and they also work reliably on the field (noisy environment, or other stuff).
Hi,
Do you belive strain Gauge module which you showing would woork precisely?
It works precisely.
@@CuriousScientist but i have to use half bridge because i need more sensitivity. These circuits are not available for half bridge commonly if you found Pl let me know
You can desolder the corresponding resistor from the board and attach the cables from the strain gauge to its place.
Thank you for this
Plz can you send the circuit of DC power supply?
Hi! All resources can be found on my website.
Did you get drift if you held a static load? I did this with an hx711 ADC and it seems to drift upwards noticeably overnight. This is very linear and im thinking of using this ADC instead.
Haven't tested it, but I can test it in the near future. When I calibrated my 5 kN load cell for my tensile testing machine, I used a HX711 for the load cell and there was a drift. But the drift was within a few grams equivalent force, so I neglected it. Also, drift can also be a creep phenomenon and not necessarily drift.
@@CuriousScientist I'm looking for an application where we are weighing for 60+ days straight without calibration. Tried the HX711 a few times now with the prototype scale. The reading seems to continue to slowly move higher after successful offset and calibration. (With two different libraries).
Ordered an ADS1256 today to feed into an Nano 33 IoT. Will also be sourcing lower resistance, higher quality strain gages.
Another trick could be to "follow" the creep of the values. You can tare the weight in certain time periods. It might worth a try. But yeah, it might be better with a custom built Wheatstone bridge, power supply and AD converter. Then you really know what you are measuring.
What is the voltage source for the HX711? Could it be changing overnight.
Reason I say this is the HX711 has the ability to control an external transistor for a stable excitation voltage. This transistor won't get used if the voltage input is lower than the excitation voltage set with a potential divider. I did a video about it recently.
hi, thnaks for your video. it is really nice. how did you oder your 350 ohms resistor ? i found 330 ohms but not 350 ohms ? have you a seller reference ? thanks in advance
Hi! I bought it from Mouser.
How about wire? please could you tell me what kind of wire you are using, if give the link like other parts will be very good?
Hi! A simple 30AWG stranded wire with silicone insulation was used at the flexible part and some 0.2 mm^2 2-core shielded wire for the signal.
*PLZ HELP*. Given a pressure of 2kpa, nominal resistance of 120 ohm, diameter of strain gauge 0.1mm, a GF of 2. What will be the change in resistance value of the strain gauge?....in short I wanta formula to calculate the change in resistance of strain gauge for a given INPUT PRESSURE
I gave an answer under the other video. But please don't spam the same question under multiple videos. Next time, I will neglect them.
@@CuriousScientist ohu I apologize
You said its the via elongating causing the resistance change? I'm not so convinced. It is the thin copper traces in the polyamide that change their cross sectional area that causes the resistivity of the trace to change. An elongated via still has the same circumference.
Where do I say "via"? I said roughly the same as you wrote here...
@@CuriousScientist at 0:34 you say "a grid or more precise the vias elongate"
Wires, but not vias. And those wires which I was referring to are the thin constantane traces applied on the polymer carrier. 😉
@@CuriousScientist aah my bad, the accent tricked me 😅. Good video sir
No worries. I am not a native English speaker, so my pronunciation can be weird sometimes. 🙃
Hello,
How can you find the stress-strain response from that data If you have the elastic modulus of that rebar? Do we need to multiply or divide the resistance of that strain gauge with the strain values, which in this case is 350 ohm?
Hi! Read upon Hooke's law for the stress-strain correlation. Or just watch my strain gauge videos where I explain it.
Hi,, the module you showed containing the bridge and opamp, found it online , is there a point on having different nominal resistance strain gauges ? if yes do you reckon i can use this module with another strain gauge ?
Hi! If you use a different strain gauge, for example a 120 Ohm one, then the output voltage of the Wheatstone bridge will be different. If the onboard resistors are 350 Ohm and the strain gauge is also 350 Ohm, then the output voltage of the bridge is 0 V, since the bridge is balanced. If you bend the strain gauge and the resistance becomes 351 Ohm, the output voltage will be 3.57 mV. This 3.57 mV is amplified further by the OPAMP. However, if you replace the 350 Ohm strain gauge with a 120 Ohm (another typical strain gauge value), then the output voltage of the bridge will be 1.22 V, without any strain applied on the strain gauge. This is not good, since if you try to apply a 10x or 100x gain on this voltage, you would reach the rail voltage (+5 V) really quickly on the OPAMP's output. And you would still need the OPAMP, because the change of the voltage on the output of the bridge will be still small.
So, in general, if your bridge consists of 350 Ohm resistors, use a 350 Ohm strain gauge, otherwise you can mess things up. If you want to use a different value, maybe add a precision resistor in series with the strain gauge to compensate for the differences. But I don't really recommend it. Use the circuit with the proper strain gauge.
thank you please the link of software
Hi! Unfortunately, the software for the PC is not available.
@@CuriousScientist how can i get similar software??please i need it
Watch my videos, I cover a lot of topics which can help you to develop your own tool. My tool will be for sale later on, but i have to find time to make it flawless and bug free.
Hey could we have access to your software please?
Hi! The software is not available for free, sorry.
Hello, how was done the treatment of the raw value data obtained with the strain gauges to get the strain?
Hi!
Everything is answered in this video: ruclips.net/video/FWRiSIqF3f8/видео.html
I have a Question
I have 5 strain gauges now I want to connect them in a single amplifier which has 5 inputs for each strain gauge
Can you recommend any amplifier which has 5 inputs for 5 strain gauges???
Hi! I have never worked commercial products, so I cannot really answer this question. But why don't you buy five amplifier modules like I use in my videos then use an ADS1256 which has 8 channels? You can build your own circuit relatively easily.
@@CuriousScientist One more Question!!!
Can we use DAQ device in place of ADS1250??
Of course.
where did you get the arduino code?
I wrote it.
Can you please share the circuit Sir
Can you please watch the video carefully and read the description too?
hi! can you please tell me what software u re using in 11,29, and what materials u used to connect voltage circuit please ? last question please
Hi! That is my own software I developed for this application. I don't exactly understand what kind of materials are you referring to. Everything is discussed in the video.
@@CuriousScientistthank u for replay, I am asking the values of capacitors that u used in the power supply circuit and the resistances in the wheatstone bridge also how did u get the 12V in the power supply ? is it an extern battery ? and the software u ve developed how can i get it ? do u sell it ? how much cost ? thank u
I don't remember the capacitor value, probably some 10 or 100 uF. The source of the 12 V doesn't matter, can be anything. The resistor values for the Wheatstone bridge is very obvious, same as the strain gauge. If you're curious about the software, contact me in email.
Can I email you about a potential commissioned project using strain gauge? Looking to build an application that is around 1 inch wide, 6 inch long, and .5 inch tall. When bent it should vibrate (using a micro vibration motor). Should have a button that allows it to be calibrated so that it will only vibrate when deviating from the calibrated strain.
Yes, you can mail me, but keep in mind that I don't do projects for free!
@@CuriousScientist I understand that 👍🏼
@@CuriousScientist What is your email?
You can find it on my website in the contact section.
would it be possible to built a small wearable application of a strain gauge that can sense and react to small strain changes? A device about an inch wide and 6 inches long and 1/2 inch thick?
It is a bit vague description. Instead of the size, you should tell the function of it.
@@CuriousScientist I mention size because I’m not sure of the size of components needed, and want to make sure such components could fit in a device this size because the application must be worn beneath the shirt
@@CuriousScientist I tried sending you an email but it isnt showing uo in my sent folder. I sent two and neither of them look like they sent. Maybe check if you got an email from brandonbaunach
Sir can u make a video on testing a concrete block using strain gauge. Plz sir.
Sorry, but I don't make videos on requests. Also, I don't have the resources to test a concrete block.
@@CuriousScientist ok sir. 👍
Hi, how did you go about calibrating the strain gauge? What testing standards are you referencing?
Hi! I did not calibrate anything. If you buy the strain gauges from good sources, they are kind of calibrated, the manufacturer provides a precise gauge factor value for it. Also, I recommend you searching for "shunt calibration".
@@CuriousScientist Thanks for the quick reply, and good video! I think I am going to be using some strain gauges for my capstone experiment!
You are welcome and also thanks! Good luck with the experiments!
Can you recommend a pletier?
What number plates work cool and consume the least amount of power?
This video is about strain gauges and not Peltier coolers.
The smaller the current (last 1 or 2 digits of the TEC Peltiers), the smaller the consumption as well as the provided cooling power.
@@CuriousScientist Tec-? Good product quality
@@ValentineDay.ForYou. Depends on where you buy it from. Some sources are not too reliable. Other Peltiers can be very expensive, even several hundreds of USD per piece.
Thankyouuu for this :D Have you ever worked with a mems sensor system in any project? That would be a really cool video
You're welcome! Mems sensors is a bit too wide field. In which application do you mean it? There are mems pressure sensors or accelerometers...etc.
@@CuriousScientist Pressure would be cool! Mems tech seemed to be the cool new pressure sensors, but I can't seem to find many demos on it anywhere. Thought it might be interesting to see you take on a project with it ^_^
hello , i hope you'll see this , i'm struggling with my project and i need some help. could you give me your email or anu social media id ? Thank you in advance
It is given on my RUclips channel and website. But keep in mind that I am not a free support service.
Someone can pass me the diagram of this circuit?
Have you ever tried actually watching the video and checking the link in the description?
@@CuriousScientist Ya but i have just a question if you can help me, this circuit is made with amplifier operationals? or not?
I was using the built-in PGA of the ADS1256.
What a coincidence! I also use this method to measure strain on alloy specimens when conducting tension, compression and axial impact test on it. Yeah, I got very tiny changes too but I was unsatisfied with that result. Anyways, unfortunately, I have not sure if my calibration method is right or wrong? Can you show me how to do calibration?
What exactly do you want to calibrate? The manufacturer already did some sort of calibration which is provided via the gauge factor. The rest of it is just mathematics, substituting the measured voltage or resistance into the right equation. Check my other strain gauge videos on the channel.
@@CuriousScientistcalibration on data logger software @picolog before starting to bend the tab/record the strain changes. I want to set the voltage reading on picolog to zero, as you got 60V at first right? mine got 50V and 70V like that... but I want to set it to zero, can't I? OR I have to substitute the value into the right equation?
Sorry, I have never worked with picolog, I have no idea about it.
@@CuriousScientist ooh.. I think the concept is same with yours only different software that we used. Its ok... So are not you clear what I meant by the calibration that I asked just now?
I really have no clue about what kind of calibration you are talking about.
Great Work!
can you please share the code for Arduino??
It is shared...
@@CuriousScientist Thank you for your attention but i couldn't find it.
can you please share it in reply?
Take your time and you can find the relevant videos on my channel or on my website where you can find the code.
@@CuriousScientist And i have few more questions. if you can tell me please.
Thank you
Ask the questions here, but keep in mind that I am not a free support service.
can you please make a video of virtual circuit of the strain guage
What do you mean by virtual circuit? Also, sorry but I don't make videos for requests for free.
@@CuriousScientist i need this circuit in matlab
Matlab is not a circuit designer software.
@@CuriousScientist simulink 😅
Still not a circuit designer tool. To design a circuit, you need something like KiCAD.
what if using four strain gauges in bridge, can the circuit still be used?
Sure. That would be the optimal solution.
@@CuriousScientist so, all dummy resistors can be replaced with strain gauges?
Yes. But be careful about how you glue them on the work piece.
Thank you very much for the answer🙏
@@CuriousScientist how to input the output to arduino?
What type of wires are those? My wires are too large to solder to the gauge.
AWG30 (0.05 mm^2) cables with silicone insulation. So they are not only thin but also super flexible.
Dear Mr. Curious Scientist,
You are doing a great job which help students like me.
Now I would like to request/seek your guidance to know more on Wireless Transmitter and Receiver modules since I want to measure the Strain/Stress/Force acting on the moving and loaded mechanical component. So I want to mount Transmitter along with Strain gauge on the test surface of the moving element and receiver placed at a distance from the transmitter need to receive the measured data from transmitter data continuously. Could you please suggest me "tutorials/learning materials/Electronic components to be used" to get to know better? I am expecting someone who would have explained like you with my requirement.
Awaiting your positive response.
Thanks & Regards
Hi!
Just search for any wireless transmission technology and apply it for your project. Read the values of the strain gauge then pass it through WiFi or Bluetooth. Any popular wireless microcontroller could do the task. Esp32 or similar. I don't know any specific creator on the contents youre asking for, but you just need to search for it on Google.
@@CuriousScientist Thanks for your kind response!
Hi! Great video! Thank you for sharing this. There is an application where I wanted to experiment with a strain gauge so ordered a similar kit ( www.aliexpress.com/item/4000907686535.html?spm=a2g0s.9042311.0.0.5e384c4dzI2ikH ), but it didn't work for me the way I thought it should. I am saying "thought", because of lack of information regarding this circuit, so I kind of guessed that the output signal is an amplified voltage proportional to the strain gauge resistance and the potentiometer is used to set the '0' voltage.
Anyway, I was reading a constant 3.46V on the output pin, regardless of the strain gauge and not even affected by rotation of the potentiometer. So I thought that I was getting it wrong and the output signal was not amplified, so went searching the internet for some info regarding this board and found your videos from which I concluded that my initial guess was correct and so my board is faulty. I ordered 2 new ones. Thanks.
Hi! Thank you! I am glad to hear that my video helped you to solve the issues!
@@CuriousScientist Hi, I got the new kits, but still have the same luck with all of them: supply 5VDC and reading constant output voltage of around 3.5V on the OUT pin, regardless of how I bend the strain gauge or how much I twist the on-board potentiometer.
What kind of signal should be output from the OUT pin? Isn't it an amplified signal which can be measured with a standard voltmeter?
Hi! Before you'd think that I forgot to answer you, I will soon upload a short video answering you specific questions. It is easier to show the things and it is more informative for you and maybe for others too. Thank you for your patience!
Hi! The response video is uploaded!
Hi! Wow! I am so very sorry to miss your last response. It's been 2 years. Thank you so much for your incredible work and willingness to help out. I have checked your response video, it is like I expected. I guess I will respond under that video. Thank you again!