Wireless Strain Gauge Possibility 1

[ManOfSteel8357]

Hi all,

My knowledge of electronics is very limited and I'm just wondering about the feasibility of a certain setup before I hire a contractor to design the apparatus. What I have is a simple strain gauge (

http://tacunasystems.com/zc/index.p...ducts_id=14&gclid=CIitx_SY97ECFUlyQgodFH0AHA)

that will be adhered to an aluminium plate being pulled in tension. Ideally what I'd like is to have the strain gauge plug into a unit that can determine the strain from the change in voltage, and then emit this data over a radio frequency (probably need some sort of amplifier and microcontroller/antenna unit). The unit needs to be compact, and be able to run for a very long amount of time without replacing the battery. The idea is that I could essentially be standing across the room with my receiver, and at any moment I could send a signal to wake the device up,and then send me back information about the current strain of the system. In addition, I'm wondering about the price of what such a unit would cost if I had these manufactured in bulk (just manufacturing cost, not design cost). No need to go into too much detail with all of this, just anything to get me stared would be great.

Thanks!
Jeff

 

[cranky108]

I don't think there is anything wrong with your idea. Although I would not ask the transmitter to analize the data, just send it. A ground based computer can analize it.

Problems to avoid: There once was a gas pressure monitor on a live tank current interrupter, that would radio the pressure to a central operator. It work great, until we had to remove the high voltage to change the 9V batterys (There were three of them).

Another company which used a fiber optic cable to transmit current levels through an insulator, used a rechargable battery with a photo cell to obtain power for there sensor. Never bought one so I don't know how well it worked.

If this strain guage were used on say a power line I would suggest a CT as a power source. But it sounds like it is not.

I have been looking for such a device as you suggest, to provide real time indication of transmission line strain (a measure of line sag). This would need to be on a bar between the insulator and line at a line dead end. An alternate location could be between the insulator and the support structure, in which case it would not be in the high voltage zone.

 

[IRstuff]

If you are sufficiently adventurous, you could roll your own, but you'd need to write a bit of code to make it work.

An Arduino board with an XBee or Bluetooth shield could be used to collect and transmit data. The processor is sufficiently powerful enough that some level of processing could even be done on board.

Nonetheless, there appears to be plenty of existing wireless solutions:

http://www.dataq.com/products/hardware/di730.htm

TTFN
faq731-376

 

[VEBill]

OP: "...be able to run for a very long amount of time without replacing the battery. ..."

Making some assumptions about the size of the battery, and how long is "very long", this requirement probably precludes most off-the-shelf SBC-based solutions.

"...I could send a signal to wake the device up..."

Another point worth considering is that it's entirely possible that a receiver with a 100% duty cycle (for the wake-up function) might require more power than a transmitter with a (for example) 0.1% duty cycle.

You might want to look into the technology used for the remote outdoor sensors used in weather stations. The default repetition rate might not be suitable, but just about everything else is.

 

[mcgyvr]

You might want to look into the technology used for the remote outdoor sensors used in weather stations. The default repetition rate might not be suitable, but just about everything else is.

I've had one now for 6 years and haven't changed the batteries yet.. It sends data every 15 seconds and runs on 4 'AA' batteries.

To the OP, your request as stated is a piece of cake with a simple bluetooth module for communication. Any contractor should be able to whip that up in a day or so. Like IR said an Arduino/xbee or bluetooth would be a great way to DIY it yourself.

 

[itsmoked]

Manufactured, something like this would be a little south of a hundred bucks in quantity.

You'd probably want to skip the receiver function as mentioned. There are other ways to trigger the processing/transmitting that would depend greatly on details of the application.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[biff44]

Took all of 40 seconds to find this:

http://www.scanimetrics.com/solutions/wireless-strain-gauge-solutions/

I think someone even makes batteryless ones for embedding in bridges, where the vibration of the bridge is harvested to generate DC for the wireless link.

http://www.MaguffinMicrowave.com

Maguffin Microwave wireless design consulting

 

[ManOfSteel8357]

Thanks for the advice everyone...this is a great start! One more question, what if we were able to plug this unit into an electrical outlet. Would it be possible to provide a large enough wireless signal so that we could monitor these gauges from very far distances (imagine a beacon on top of a mountain...on the order of a couple hundred miles)? Someone suggested using internet, but this seems far more difficult and expensive. Thoughts?

 

[ManOfSteel8357]

For example, would it be possible for this unit to send a radio wave of data from Los angeles, and then have a receiver be able to pickup the signal in SF?

 

[VEBill]

Radio communication over any clear 'line of sight' path is basically "trivial" (a slight over-simplification). Going 'Beyond Line Of Sight' typically requires satellites or reliance on ionospheric refraction (HF). So it all depends on the path.

 

[VEBill]

You posted at the same time as I did.

LA to SF is not 'line of sight'. Thankfully, both are highly populated areas with commercial communications providers that make data transmission too easy.

 

[IRstuff]

Cellular phones can cover most metro areas.

TTFN
faq731-376

 

[cranky108]

It would be easy to insert the information into the radio signel. But not being a broadcast engineer I can't tell you how.

Many power companies, at one time, used a carrier wave to control remote capacitor banks.

However with a remote transmitter site I would think there would be a transmitter statis back to the controling location. So maybe over that service communications channel.