Analog sensor long range

[BTCAD]

Hi,
     how can I read an analog sensor over km? Cable isn't a good way I think because of interferences and voltage drop into the cable. Does it exist a kind of wireless transmitter of wired transducer or converter? I saw a lot of device on the net but i don't know if it's realy reliable.
 
 
 
Any suggestions?
 
 
 

 

[CAI_Support]

Can you use a WC8 to read then WEBSET to your WC32 board or your server?

 

[rossw]

Hi,
     how can I read an analog sensor over km? Cable isn't a good way I think because of interferences and voltage drop into the cable. Does it exist a kind of wireless transmitter of wired transducer or converter? I saw a lot of device on the net but i don't know if it's realy reliable.
 
Any suggestions?

 
More information will help us. On the face of it, and in the absence of more data - 4-20mA loop is perfectly capable of reliable operation over that distance (and substantially more). (I've just shipped a whole bunch of my terminal/amplifier boards set up for 4-20mA input for just such an application)
 
In the past, I've used both radio and optical systems over distances around 10km, sending PWM or variable-frequency, to carry analog values. The WC8 can use input 1 as a frequency input.

 

 

[BTCAD]

PSAN-V01CV-Rc1/8 NPN from Autonics.
 
 
I want to read this 0-5v output over 1.5km aprox.
 
There is no energy source where the sensor will be installed. I can use a little solar panel and a battery. So the lower the energy cumsuption, the smaller the battery and solar panel.
 
I can use fiber optic and 2 media converter to read webset from a wc8, or coax over lan up to 6000' but i'm affraid by the power cumsuption. A wireless solution could be the best but radios need a lot of energy to work. 

 

[BTCAD]

http://store.iteadstudio.com/index.php?main_page=product_info&products_id=127
 
This is a little rf transmitter and receiver. I have 4 kits on my table. I d'ont know if I can use a wc8, the analog sensor and the transmitter to read and send data to the receiver. ?,,,?,,
 
 
A kind of binary code encoded from the wc8 and decoded from the wc32. I don't need something fast. only 1 refresh every 30sec should be perfect.
 
What do you think about that? 

 

[rossw]

I want to read this 0-5v output over 1.5km aprox.
 
There is no energy source where the sensor will be installed. I can use a little solar panel and a battery. So the lower the energy cumsuption, the smaller the battery and solar panel.

 
One of the major benefits of of 4-20mA loops is that you don't NEED any power at the sensor end, it comes down the line.
Your instrument however may require more than 4mA to operate, so you might need some extra power for it.
 
Converting 0-5V into a 4-20mA signal is straightforward. An example of a simple circuit that will do it is here:

 
At the other end, you may get away with something as simple as a 500 ohm resistor (two 1K/1% in parallel) will give you 10V out at 20mA
Using a smaller sense resistor and an opamp is preferable however. (I usually use 33R or even 100R).
 
Using an 8-bit binary coded signal reduces your resolution to only 256 steps which is getting pretty rough!

 

[BTCAD]

What do you mean by 256 step?

Is the total reading sepetate in 256? If so, it shoukd be correct for this apolication

 

[rossw]

What do you mean by 256 step?

Is the total reading sepetate in 256? If so, it shoukd be correct for this apolication

 
The analog inputs on WC8 and WC32 are 10-bit ADC. That is, they have 2^10 discrete voltages they can differentiate, or 1024 levels. So a 0-10V signal can be read to (near enough) to 10 millivolts resolution.
 
If you operate the 8 outputs, it can only present 2^8 discrete states (256 levels).

 

[CAI_Support]

What kind of connection do you have between the board and sensing location?  How often do you need to measure the analog input?  For 1.5km distance, it is hard to read analog input by place sensor that far away from input.

 

[BTCAD]

Every minutes could be correct. NOT MORE
 
 
I don't have acutally any link between remote sensor and wc32. 

 

[rossw]

I don't have acutally any link between remote sensor and wc32. 

 
The distance involved is easily done with a simple low-power radio. Keyed or FSK, one bit at a time, low bitrate. I have already written code to send multiple 16-bit words between WC8 boards at around 10 bits per second, could be easily adapted for your needs.
 
At the sender end, perhaps a little PICAXE chip (includes analog inputs), let it key a small transmitter to send low-speed serial data, and have the webcontrol receive it a bit at a time. Picaxe standby current is in the low-milliwatts to microwatts range. Sending values once a minute, I expect 3 AA cells would last months.

 

[BTCAD]

Interresting.
 
 
Rossw , can you share your code here?
 
Wich transmitter did you used??
 
 
PICAXE model number?

 

[rossw]

Rossw , can you share your code here?

When I get a minute, sure.
 
 

Wich transmitter did you used??

 
In my case, I was super-imposing an extra 100mA on the supply line (roughly). I had several devices on the far end of a power run, I could address each by pulsing the voltage between 12V and 24V, and the remote end could communicate back by loading (or not) the line a little, which I could read in the WC8 at the head end.
 
Because of the long cables, and filter capacitors etc, a few bits per second was as fast as I dared go.
 

PICAXE model number?

I was using 14M2 devices, because I was reading 3-axis accelerometers and operating PWM outputs etc, but an 08M2 would do your job fine.

 

[BTCAD]

Yes O8m2 have some analog input.

So if im right, i can use this mcu with a analog sensor then send the data to a rf transmitter. From the other end, receive data and send it to wc32. It will be a low comsuption system!

 

[CAI_Support]

If you are have two wires, you can run that over the I2C bus, since that can run on any clock speed, to transmit data.  SPI bus is also fine, one clock line, one data line.