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Hi,

i am trying to measure the water level with using a pressure sensor:
http://www.meas-spec.com/product/t_product.aspx?id=2894

It has 4 pins : supply(+ and -), output (+ and -)

how can i connect this transducer to arduino.
It tried this configuration >>
supply +    to  5V
supply -    to  GND
output +   to A0
but i am getting always this result on screen (serial monitor):
although the water level is constant i get the value between 1023 and 0 which is allways repeating like a sinusoidal form.

then i tried this configuration :
supply +    to  5V
supply -    to  GND
output -  to A0
this time i get always the value 103 in serial monitor. what does that mean?

could you help me please?

thanks



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What is the model of the sensor ? It should be something like this: US381-000005-500PG
The model specifies which type it is. They are made with 4 different connections and for a number of pressure ranges.



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thanks for instant reply.

yes u are right.
it is US331-00005-500PG.

i saw 4 cable in this model but not sure all of them are available.
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If it has 4 wires it should be with mV output, US321
If it is US331, it should have 3 wires.
I'm sorry, but I don't understand why you have 4 wires, and I don't know why you have such readings.
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i want to comment in a different view.

i am observing 103 in serial monitor when i connect it with arduino. so i think that means:

sensor range is : 0 to 30 bar= 0 to 300 meter water level
sensor output is : 0.5V to 5V

arduino analog range: 0 to 1023 = 0 to 5V
i observed the value:  103 which means 0.5V in sensor output == 0 bar == 0 meter water level..   CORRECT 

but i think so this sensor is not suitable for me with respect to RESOLUTION :
0.5 V to 4.5 V == 0 bar to 30 bar
133mV == 1 bar == 10 meter water level
133 / 5 mV  == 27 unit  == 10 meter water level
2.7 unit ==  1 meter water level

so when the water level changes 1 meter, serial monitor in arduino show a change of 2.7 .    come on, which is not a good value to observe in serial monitor. It is so difficult to attain this resolution.

Am i right???





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Am i right???

Yes. There is a basic trade-off of range of primary measurement and resolution limited by the arduino 10 bit ADC converter. You can select a sensor with a lower total range or use an external ADC converter that has better resolution (more bits of conversion).

Lefty

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Am i right???

 You can select a sensor with a lower total range or use an external ADC converter that has better resolution (more bits of conversion).

thank you for ur precious reply.
- i think the pressure sensor resolution is 13.3mV for 1 meter water level, but arduino has 5mV resolution.
So it is difficult to capture the water level of 0.1, 0.2, 0.3 meters?

- what do u mean by external ADC converter, i dont know it?
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Quote
Am i right???

 You can select a sensor with a lower total range or use an external ADC converter that has better resolution (more bits of conversion).

thank you for ur precious reply.
- i think the pressure sensor resolution is 13.3mV for 1 meter water level, but arduino has 5mV resolution.
So it is difficult to capture the water level of 0.1, 0.2, 0.3 meters?
That is correct, the 10 bit ADC limit does not allow you the resolution you desire. Solution, sensor with smaller range or ADC with better resolution.
- what do u mean by external ADC converter, i dont know it?

Something like this: http://www.adafruit.com/products/1085
Lefty

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Isn't sea level air pressure around 1 bar?

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Isn't sea level air pressure around 1 bar?

10meter  water level pressure = 1 bar

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Isn't sea level air pressure around 1 bar?



Depends on if the sensor is a PSIG or PSIA type. Gauge pressure sensors will read 0 bars at sea level, Absolute pressure sensors read 1 bar at sea level. All pressure sensors really have two sensing legs, one an internal reference port and one brought out for user's connection to his/her process.

 A gauge pressure sensor's internal reference is whatever the actual ambient pressure is and a absolute pressure sensors has it's reference port evacuated to as complete a vacuum as possible and sealed. A differential pressure sensor brings out both sensing ports for user's use.

Lefty
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That pressure gauge is used for HVAC and needs to measure how much vacuum a pump is pulling in a line, how close to ZERO pressure, ie vacuum.

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10meter  water level pressure = 1 bar

Why would that gauge return pressure minus 1 atmosphere?

Same way I learned in school:

Quote
P = a+l*g*h
where
P = water pressure (hydrostatic)
a = atmospheric pressure at water's surface
l = water density
g = gravitational acceleration
h = water height

9.81 meters under fresh water the pressure should be 2 bars on a 1 bar atmosphere day.

I live in close to 1 bar atmosphere here at over 1200 ft alt (more than 300m). But today we have high pressure weather, 30.2 inches with standard day at sea level at 29.9 inches.

To get water depth right regardless of weather/altitude you will need two gauges. One just for the correct air pressure as that pushes down on the water and ADDS to water pressure.

That should change your scale at the very least.




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could you please help me on cable CONNECTIONS please?

the pressure gauge or absolute is not a problem for me, i just want to learn how can i connect this type of sensor in ARDUINO....

 
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I'm just going to keep the datasheet open....

I see a cable with 4 wires and no connectors with 4 pins.
The cable with 4 wires is the mV cable and then you need to know what length to get the CODE # and still on page 4 there's reference to Code 8 while neither Table 1 or 2 has a Code 8.....

maybe ask them for a decoder ring. I sure don't know.

Best I can see is +Out (Green wire?) should be Output. -Out is N/A all but the 10mV/V, maybe a test line.

Output --- the Green wire
10mV/V (ratiometric)
0.5 – 4.5 V (ratiometric)
1 – 5 V
4 – 20 mA

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