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juicebiz
Joined: 31 Aug 2007
Posts: 1
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 31 Aug 2007 19:10 Water/Fuel Sensor: Resistance to Voltage Converter |
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I want to monitor the water level in my RV tanks. There are resistance sensors available that have a float on a tube. When depending on where the float is on
the tube, the resistance is different. Here are some examples:
http://www.wemausa.com/tank_sensors/tank_level_sensors.htm#Fuel_Water_Tank_Sensors
I want to convert the resistance to a voltage 0 - 10 VDC and put it on a sensor in order to monitor it on my laptop using this software:
http://www.dataq.com/products/startkit/di194rs.htm
Any ideas about how to approach this is greatly appreciated.
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prashar
Joined: 15 May 2007
Posts: 11
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| 31 Aug 2007 19:23 Re: Water/Fuel Sensor: Resistance to Voltage Converter |
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| hi, I too want to make a water level controller.will you please tell me how these sensors work? Is it just like a variable resistor giving different ohms between two terminals depending upon the position of the float? THANKS. PRASHAR. prashbh(at)gmail.com
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Rexypoo
Joined: 21 Dec 2007
Posts: 6
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| 08 Feb 2008 5:41 Re: Water/Fuel Sensor: Resistance to Voltage Converter |
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You should double-check my suggestions before putting electronics near a fuel pump. Just be cautious and make sure there's no risk of getting a short circuit.
One method of getting a specific output voltage for a given resistance is to use a constant current source.
The basic concept is described on wikipedia: http://en.wikipedia.org/wiki/Current_source
I would recommend using the op-amp and transistor circuit pictured here: http://upload.wikimedia.org/wikipedia/en/9/97/Op-amp_current_source_with_pass_transistor.png
The website you provided has very little information, so I used this site as a reference for the pump's operating resistance:
http://www.kupo-sensotex.com.tw/sfw.htm
assuming a 5.1v zener diode (http://www.radioshack.com/sm-more-product-information-for-the-1n4733a-1w-zener-diode--pi-2049726.html) you can use the following resistance values
for the sensor with a 0-180 ohm range the "sense" resistor should be a 910 ohm resistor
for the sensor with a 30-240 ohm range the sense resistor should be 120 ohms, however this sensor will not go all the way down to 0 volts
remember to avoid high voltage, the 12v car battery should be enough to power the circuit, or if you have to use a power jack plug in a 12v-15v adapter
in response to prashar's question of "how do these sensors work?" I suggest reading the wikipedia entry on level sensors
http://en.wikipedia.org/wiki/Level_sensor
I would expect a fuel sensor to be a pneumatic sensor. In this case basically the shaft contains a bubble which exerts pressure on the top based on how deeply it is immersed. This allows the electronics to be mounted outside fuel tank to reduce risk of electrically igniting the fuel.
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