50 channel strain sensor help!

[Fieryfire]

Hello guys,

I have a project that requires that I have a sensor network with 50 sensors that are to be converted to adc and preferably sent via wireless packets to a cloud. I must say that I am using a pre-built sensor for for measuring strain, I need to understand how I must proceed with purchasing the remaining units and as efficient and simple as possible. Via ADC, WiFi transmitter, cloud storage, etc. It's relatively simple I guess but could anyone kindly help me to decide the best possible approach to go about this project. It will be really helpful. Thank you

 

[Les Jones]

You will need to provide more details. First when you say you have pre-built sensors do you mean just the strain gauge or a strain gauge with an amplifier ? If it includes the amplifier what is the signal level output from the amplifier ? Will all the sensors be connected to a central point and then the data sent via Wi Fi or will each sensing point have it's own Wi Fi connection. Are the sensors just to be scanned in sequence or will the central unit send out random requests for a reading ? How quickly do you need each reading to be taken ? That is all the questions I can think of at the moment but there will probably be more as people come up with possible solutions.


Les.

 

[Fieryfire]

Thank you Les for the reply. At the moment i just have the strain gauges without any kind of amplifier and it is resistive based. so i suppose that a kind of wheatstone's bridge is necessary to measure the voltages from each of the 50 strain gauges??? After that i am unsure of how to proceed. My requirements are that the acquisition speed/frequency should be at 1000Hz. and the sensors must all be sending the information simultaneously through the wifi(preferably) to a cloud or serially captured to an excel file. It could be a trigger based or a continuous acquisition. Could you kindly help me out ?

 

[Les Jones]

The method of reading the load cels that I was thinking of suggesting (HX711 24 bit A to D converters.) would not be fast enough to give the 1000 readings per second from each load cell. Their maximum speed is only 80 readings per second. There are other people on this forum that have experience in the use of load cells that will probably be in a better position to help you.

Les.

 

[Reloadron]

You are looking at what will become an expensive project. Here is an example of an inexpensive DT85 Data Acquisition System which is a cheap 48 analog channel unit. Personally I would break the project down and start with the data acquisition portion. You will need 50 analog channels and based on your sample rate a 50 kHz sample rate. For high speed scanning I would look to Agilent Data Logger Systems and use their software, that or write your own. With your requirements, be it in a cloud or wherever you are going to generate a huge pile of data. I would store it locally and then at intervals move it to a cloud. You mention WiFi? Why is WiFi required? There are WiFi data acquisition systems but unless you need to move data using WiFi I would avoid it. I would look at data acquisition systems which offer solutions for completing and exciting your strain gauge sensor bridge. You are looking at a costly system so before going very far what is the budget? Anyway, I would get an Agilent applications engineer or you could try an Omega applications engineer. National Instruments is another possible hardware and software solution and they also have very good applications engineers worth a call.

Ron

 

[Les Jones]

Hi Fieryfire,
I'm not sure that you undersatnd how weighing systems normaly work. A load cell (which measures the force.) normally uses four identical strain gauges arranged in a wheatstone bridge. Two of the strain gauges are positioned on part of the structure that is compressed when the load is applied and two are positioned on parts that are stretched when load is applied. This increases the sensitivity. This arrangement also cancels out resistance changes in the strain gauges caused by thermal effects.
Hi Ron,
I've just had a look at the link that you posted and noticed that the maximum sensing speed is only 25 HZ. I have no practical experience of strain gauges but my feeling is the Fieryfire's requirement of 1000 readings per second from each load cell will be difficult and expensive to achieve.

Les.

 

[Reloadron]

Hi Les and I very much agree this will be an expensive endeavor. My first link was a cheap example, once we get into the Agilent and NI solutions there will be considerable cost.

Ron

 

[ronsimpson]

1000Hz. and the sensors must all be sending the information simuoltaneously through the wifi(preferably) to a cloud or serially captured to an excel file.

Are all the sensors at the same location? or they feet or miles away?

We must know what resolution you need to measure. (Resolution and speed) One example, from above, 24 bit at 80hz. But at 16 bit you could measure 100,0000 time a second. Resolution = 101 or 100.1 or 100.01 or 100.001 ????? Cost = resolution X speed X number of channels. At 16 bit you can only measure to 65,000 so you can see the difference between 65,000 and 64,999. 24 bit = 16,777,216 max count. Big difference.