Pressure transmitter for tank's water level measurement

Guys , I am looking for a pressure transmitter with following specs :

Measurement type : Gauge pressure
Range : 0.0 bar - 0.2 bar
Output : current or voltage

I want to use this with an Arduino board to display the level of water in a tank .

While there are many available out there , but I need a one that is inexpensive ( available in India for less than 500 Rupees ) .

Please suggest if you have came across one .

Thanks

500 rupees is 7.5 dollars.
200 mbar is 20 kPa or 200 hPa.
A gauge pressure sensor measures the pressure relative tot the normal air.

Do you want to submerge the sensor, or are you using a tube and measure the pressure at the top of the tube ?

Instead of a gauge pressure sensor, perhaps you could try two BMP085 or BMP180 chips. One in the tank/tube and one outside the tank for the air pressure. Calculate the difference.

On Ebay are many MPS20N0040D for less than 2 dollars. But you need to amplify the output.
Perhaps you can use the outputs for a very rough indication of the pressure, or you might use the internal analog amplifier of the Arduino Leonardo and Arduino Mega 2560 (the Arduino Uno doesn't have the internal analog amplifier).
The internal analog amplifier is not used a lot, you probably need some help to program the registers, and I have not used that yet.

On Ebay are also many pressure sensors for cars, for under 10 dollars.

Koepel:
...or you might use the internal analog amplifier of the Arduino Leonardo and Arduino Mega 2560 (the Arduino Uno doesn't have the internal analog amplifier).

I have a Mega, and would like to know how to use the "internal analogue amplifier".
Which page of the datasheet.
Leo..

Open the "Complete" datasheet from here : http://www.atmel.com/devices/atmega2560.aspx
Go to page 283.
It is a lot like a instrumentation amplifier, two high impedance inputs, positive and negative and a programmable gain can be set to 1x, 10x or 200x. The internal reference of 1.1V can not be used in differential mode. The resolution will be less than 10 bits. The voltage should be calculated with a factor of 5.0 / 512.0 instead of 5.0 / 1024.0.

Keep the pinmapping page nearby : https://www.arduino.cc/en/Hacking/PinMapping2560
ADC0 and ADC1 are A0 and A1.
ADC2 and ADC3 are A2 and A3.

It is a nice feature, I wonder why it is not used more often.
This makes it hard to understand : "The 16 channels are split in two sections of 8 channels where in each section seven differential analog input channels share a common negative terminal (ADC1/ADC9), while any other ADC input in that section can be selected as the positive input terminal. If 1x or 10x gain is used, 8 bit resolution can be expected. If 200x gain is used, 7 bit resolution can be expected.

BMP085 or BMP180 are very good options for short length data connection , however the water tank is located about 20 mtrs away from the Arduino .

I intend to place the sensor in the tank ( submerged or tube ) and use long wires ( 20 mtrs ) to power it and to transfer signals .

20 meters is not possible with the normal I2C bus. There are special chips for I2C over long wires, or you have to use another bus.

If I see any more cross-posts of this topic or thread-hijacks, there'll be a forum timeout.

Clear?

AWOL, please explain.
The cheapest pressure sensors contain only a wheatstone bridge, and some ATmega chips have an internal differential gain (so an external OpAmp is no longer needed), and many new Arduino users think that the I2C can be used with long cables. So far nothing out of the ordinary.

What's to explain?
I've deleted two copies of this topic in other unrelated threads.
If I see any more, the OP gets a forum timeout.
Simple enough?

Yes, thanks for explaining.

Koepel:
It is a nice feature, I wonder why it is not used more often.
This makes it hard to understand : "The 16 channels are split in two sections of 8 channels where in each section seven differential analog input channels share a common negative terminal (ADC1/ADC9), while any other ADC input in that section can be selected as the positive input terminal. If 1x or 10x gain is used, 8 bit resolution can be expected. If 200x gain is used, 7 bit resolution can be expected.

It is a problem of noise floor. At 10X don't expect to read better than 1:256.
For 200X don't expect to read better than 1:128.
Note also that resolution is not the same as accuracy.
Dwight

It would be good enough if a cheap solution is required. The numbers in the datasheet are without averaging. Small changes can still be detected I think with software averaging.
I see many of these on Ebay and dx.com and Banggood and other websites : http://www.ebay.com/itm/131546887010

This is a tutorial for them : http://langster1980.blogspot.nl/2014/11/how-to-use-pressure-sensor-with.html
In that tutorial a OpAmp is used, but a instrumentation amplifier should be used instead. A OpAmp disturbs the wheatstone bridge of the sensor.
I think that using the internal differential gain would result into about the same accuracy as that circuit.

Why not use a capacitive sensor?
You should only need a wire loop hanging in the tank.
Dwight

Is BMP 180/280 waterproof sensor ? How can I submerge it inside water ?