# fluid level

#### picit

Joined Dec 14, 2007
7
I have a water tank (4'x4' x3' )that i want to bury up hill from my camp and fill it with a well pump and generator and then gravity feed camp so i won't need electric running.
My problem is knowing water level in tank. Is there a variable resistor that works on a cable, so i can mount one end on a float and the other end on top of tank?
Any other ideas would be helpful

thanks

#### beenthere

Joined Apr 20, 2004
15,819
Two float switches might be more simple. The lower turns the pump on when it falls, and the upper turns it off when it rises.

#### picit

Joined Dec 14, 2007
7
THanks beenthere

I'll try that if i can't find way to read the full swing 1/4,1/2,3/4 like a gas tank.

#### kammenos

Joined Aug 3, 2008
127
You want to know 1 or two levels? Or exaclty the level ? I mean, you could use a probe or two (like beenthere said) but if you want to have an analog signal, then you sjould consider using a pressure sensor. Water is what you will fill the tank?

#### thingmaker3

Joined May 16, 2005
5,084
One can purchase resistive water level sensors which function similarly to automotive gas tank sensors. Here is one example: http://www.wemausa.com/tank_sensors/tank_level_sensors.htm

They are a bit expensive, especially when compared to a ping-pong ball on a stick with a hand-full of scrounged micro-switches.

#### beenthere

Joined Apr 20, 2004
15,819
External hardware amy be hard to maintain, as the tank is going to be buried.

Question - is it important to know the fill level, or will it be enough to insure the tank is never empty?

#### SgtWookie

Joined Jul 17, 2007
22,210
Well, the S3U with a 35" vertical dimension is $69, and then the OP will need the$4 adapter plate for mounting it. It's made from 316 stainless steel, so he should get a long and trouble-free lifetime out of it - if the interface electronics are properly designed.
It has 240 – 30 ohm operation; that seems to be in the ballpark range of a typical fuel tank level sender. He wouldn't even have to build any electronic interface if he didn't want to - just run a couple of wires down to the camp, and use a multimeter set to read Ohms. 30 Ohms = nearly empty, 240 Ohms = full. Since a 4'x4'x3' tank holds 359 gallons, if the OP multiplies the Ohms x 1.5, they'll get a pretty reasonable estimate of how many gallons are left.

#### picit

Joined Dec 14, 2007
7
Thanks All

The tank will be underground but will be accessible. The S3U looks like it will fit the job as i already have 3 wires buried up to the tank.

Thanks again
Picit

#### SgtWookie

Joined Jul 17, 2007
22,210
I'd go for that solution myself. It'll be worth a few extra bucks for the extra reliability.

Don't forget that your wire that you ran will have some resistance to it. Exactly how much depends upon the wire gauge and the total length of the wire (round-trip). You'll need to subtract that wire resistance to get the actual resistance of the level sender.

If you're going to bury the connection at the water tank, better use waterproof heat shrink tubing; the kind with glue inside. Electrician's tape is garbage; it'll fall off in a few months. Silicone RTV is corrosive; it emits ascetic acid as it's curing.

#### thingmaker3

Joined May 16, 2005
5,084
Electrician's tape is garbage; it'll fall off in a few months.
Its not "garbage," anymore than a butter knife is "garbage" when a screwdriver is called for. Butter knives work quite well for spreading butter or jelly, just not for putting in screws. Electrician's tape is perfect for temporarily securing cables or wires onto a pull-string or fish-tape. The colored varieties are good for identifying cables. It should never be used as an insulator, though. Use "self-fusing silicon tape" for insulating.

#### SgtWookie

Joined Jul 17, 2007
22,210
Its not "garbage," anymore than a butter knife is "garbage" when a screwdriver is called for. Butter knives work quite well for spreading butter or jelly, just not for putting in screws. Electrician's tape is perfect for temporarily securing cables or wires onto a pull-string or fish-tape. The colored varieties are good for identifying cables. It should never be used as an insulator, though. Use "self-fusing silicon tape" for insulating.
Yeah, OK - it does have some minor (and temporary) uses; just not for what most people think it should be used for.

I found some guy last summer using electrician's tape on a homebuilt aircraft. I nearly had a conniption fit.

I personally love the self-fusing silicone tape, but it's difficult to find, and takes some practice before one can apply it properly.

The heatshrink with the glue inside is relatively easy to use, and won't leak for quite a while.

#### thingmaker3

Joined May 16, 2005
5,084
I found some guy last summer using electrician's tape on a homebuilt aircraft. I nearly had a conniption fit.
YIKES! Step away from the aircraft, Sir!

I personally love the self-fusing silicone tape, but it's difficult to find, and takes some practice before one can apply it properly.
Yes, now that you remind me of it, I do recall a bit of a learning curve for the silicon tape. For a one-off, the goo-tube would indeed be better.

For finding the self-fusing tape, try asking for "tommy tape" or "wrap fix" at your local hardware or farm supply store.