Hi.
Im planning to connect water probe to my arduino uno.
This probe uses just two wires and resistor values are from 1 - 190 Ohm ( based on slider movement )
What would be a best way to connect this to arduino ?
One line to analog input , one line to gnd. ?
Do i need to add something...
Arnix
These values are rather low, so it's best to measure with a low voltage, to reduce current draw.
I would connect the sensor between analogue input and ground.
And use a 750ohm (2x 1k5 in parallel) pull-up resistor between analogue in and 5volt.
The sensor voltage will then vary between ~0 and ~1volt.
Then read the sensor with analogReference(INTERNAL); in the setup.
That will use almost the full range of the A/D.
Write/use a sketch that displays the A/D value on the serial monitor.
Leo..
Maybe it would be better if I more details.
I am planning to use this probe as some kind of alarm.
The probe should trigger alarm when water level starts to drop faster then it suppose to do.
The water tank is holding water for few hours, then it starts to empty itself under some predefined conditions. This is the process that i need to monitor.
Arnix
I would use a 100 Ohm pullup resistor, and even that won't work well when the sensor resistance is less than 10 Ohms.
"This probe uses just two wires and resistor values are from 1 - 190 Ohm ( based on slider movement )"
That range is unusual. Can you verify that with an ohm meter.
Would it be easy to switch to a probe with higher resistances (1k-30k range)?
I can imagine that 1 - 190 Ohm may present some obstacles with arduino.
I can add some LM358 circuit so i can get higher voltage range but i dont know how precise will this be.
Something like 24V input / Vout ( 1-24V ) / probe.
On the other hand, in this case i need additional HW.
I can verify resistor values but i think that this is correct range.
A.
jremington:
I would use a 100 Ohm pullup resistor, and even that won't work well when the sensor resistance is less than 10 Ohms.
The way I have explained it you will have at least FIVE digital steps per ohm.
So 1ohm is easy to detect.
Leo..
This could be a fuel sensor, used to drive an analogue meter directly.
Why would a 750ohm - 190ohm resistor divider be a problem.
Leo..
Can you provide us a web page for this probe?
Are you interested in measuring the full range of the probe, or are you interested in a sub set of that range?
I had a small (300 gallon) water tank I wanted to check. After all considered, I decided to put a float switch at max level, at low level, and just for good measures at mid range. Three on/off switches for my needs.
But if you want to tell how fast it is filling or emptying, that probably would not work for you.
The way I have explained it you will have at least FIVE digital steps per ohm.
So 1ohm is easy to detect.
Not really, considering noise.
jremington:
Not really, considering noise.
Digital values can jump +/- one digit, but please explain what you mean with noise.
Leo..
Edited:
There one more thing with this probe. I have test it with LM385 pcb and directly.
Regardless if the measuerment is defined as voltage or resistor value, there is one problem.
If the slider moves slowly, multimeter can not detect changes ( maybe arduino will detect this ).
This happens regardless if the slider is on the bottom or the middle or the top.
When i look this, then i have a big problem. I can loose quite big amount of water before i can detect that something is wrong.
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@wava & jack_wp
Link to datasheet
The probe can be used as fuel probe but at the moment we are planning to use it in water tank.
Future project can include fuel level measurements.
Are you interested in measuring the full range of the probe, or are you interested in a sub set of that range? *** Main goal is to track down if the water / fuel "leaks" down faster than it soposed to do. E.g. if your tank if 20% full and you know that tank releases cca 1 litre per hour, then anything faster then that should trigger alarm. It's important to write that the "leaking" process depends on few things so it will not be the same every time and in every tank.
Maybe the fuel tank would be a better example. You are driving with your 50% full tank.
At some point fuel level starts to sink faster then normal ( this part must be calibrated ).
If the program reads this state, alarm should trigger.
Test scenario:
Tank full --> flow rate ( 1 litre under 10 minutes )
Tank full --> flow rate ( 3 litre under 10 minutes ) --> alarm
Btw. i have created one external pcb with LM358N. If i hook up 24V to this PCB and probe on the other end, i can get Vout from 1-24V. Maybe this would solve the problem. Unfortunately it will raise the production costs....
A.
Datasheet:
"The sender gives several equal steps to the gauge"
What does that mean.
Is this a digital sensor.
How many steps can you count.
Leo..
edit:
found this page.
The magnet switches a series of reed contacts.
http://www.wemausa.com/sensors/level-FuelWater.shtml#.VcMpP_nCfao
Not sure if your sensor is the same.
http://www.wemausa.com/sensors/level-FuelWater.shtml#.VcMpP_nCfao
Yes, this is the probe that i have. But it's SE standard ( 0 - 180 Ohm ).
S5- E250
A.
Seems that all these sensors have reed contacts, with a spacing of 10-40mm depending on the sensor length.
S probably stands for stainless, and E for the European resistance 0-180ohm standard.
These sensors seem to work in STEPS, not lineair.
There are also lineair capacitive sensors from that brand.
http://www.wemausa.com/sensors/level-Capacitance.shtml#.VcM39_nCfao
Leo..
You may want to keep this sensor, but one suggestion:
since your main concern is how fast the water is dripping, maybe a pair of stainless steel wires in the water tank, and measure the change in resistance as the water drops, and how fast.
Thank you for your suggestion.
I can not add additional measuring parts because i have to use this kind of probe.
I will contact the manufacturer to see what they mean about whole situation.
Nevertheless, how would you connect this probe to get optimal reading values (including the values under 10 Ohm)...
btw. if we decide to go with CLS version, what then. How to connect that probe ?
"Btw. i have created one external pcb with LM358N. If i hook up 24V to this PCB and probe on the other end, i can get Vout from 1-24V. Maybe this would solve the problem. Unfortunately it will raise the production costs...."
I suggest this method to give accurate, and safe input. You should be able to adjust the gain on the 358 to give the voltage range that the analog pin can accept (0 - 5v), so no voltage divider needed there.
I use an ultrasonic sensor to measure water level. It has worked reliably for me for 2 years now.
@dougboy
Thank you for your suggestion. Unfortuntaly, the probe should work in water and fuel systems so i have to go with such solutions. Anyway, your project is quite interesting !
@jack_wp
I have contact the reseller and this is the answer that i got:
Hi
You can use the CLS senders :
The Capacitance Level Sensor (CLS) is used to continuously detect fuel level by measuring the capacitance variation as the level changes. It is ideally suited for anti-siphon, fuel-theft detection, and fleet management applications. The CLS should NOT be used for measuring water level, or levels of other conductive solutions and if you would like stay with the kind of sender you have, we can make a float sender with a linear output and we also make senders with 4-20mA , 0-10volts, 0-5 volts. I have attached a custom sender sheet for you to fill out and send back.
Arnix