Long range wired >1km pressure sensors

Hi All,

Wondering if I can get some help.

I am trying to set up a series of pressure sensors (about 15) over a long distance (about 1km)

Since I will not have power at these points and I need reading over a long period of time, a wired solution is preferred.

What wire can I use? Is there a one wire sensor that will work? What other factors do I have to consider?

first thing to consider is what he range of the sensor should be, furthermore the frequency of readings. for 1 KM RS485 is probably the way to go, it is serial in a robust way.

That is too long to send an analogue signal over unless you have some conditioning at the far end. For example encoding the sensor information with a 4-20mA current loop. That means having electronics at the far end and supplying power to it. That means at least having a 3 core cable connecting the two.

I would not use RS485 because that would involve having an Arduino at both ends.

I would look at an RF solution with a system that will set up its own mesh, Xbees would be my drink of choice here. Use small solar cells to keep batteries charged and only broadcast the sensor readings as often as needed. wade

Any idea how many Xbees it would take to cover a distance of 1K?

I would say that depends on the Xbee or Zigbee model being used: http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/

4..20 mA sensors do only need a 2 wire cable. But we are talking industrial sensors here and the do not come cheap. Here is a paper how to conatruct one yourself http://cache.freescale.com/files/sensors/doc/app_note/AN1303.pdf Here is one for purchase: http://www.omega.com/pptst/px182b.html

Thanks.

Nilton61

Do you think I would get away with something like this? how could I connect several sonsors on one cable?

Thanks!!

http://www.digikey.com/product-detail/en/MPX5100DP/MPX5100DP-ND/464060?WT.srch=1&WT.medium=cpc&WT.mc_id=IQ66882679-VQ2-g-VQ6-53963506155-VQ15-1t1-VQ16-c

nilton61: 4..20 mA sensors do only need a 2 wire cable. But we are talking industrial sensors here and the do not come cheap. Here is a paper how to conatruct one yourself http://cache.freescale.com/files/sensors/doc/app_note/AN1303.pdf Here is one for purchase: http://www.omega.com/pptst/px182b.html

If the sensors are closer to each other that to the receiving point you could use a common supply wire. The number of wires in the cable will then be NumberOfSensors+1

Grumpy_Mike: Any idea how many Xbees it would take to cover a distance of 1K?

I have gotten a strong signal at 1,000 yards with the 100 mW 900 MHz units with a simple dipole, rubber duck, antenna.

When it matters the XBees work very well and are worth it.

wade