tank pressure sensor any electronic engineers on here ?

Entropy would suggest otherwise. Over time, the air will tend to dissolve into the diesel, or otherwise escape ... the general trend is that over time, the pipe will become full of diesel.
 
I only have a v. vague idea about entropy and on a slightly different context, so I'll just pass and fit the sensor at the bottom just like the water one (no big deal)

cheers

V.
 
In the industrial world of level measurement you have a choice of dry leg or wet leg measurement and the option of sensor positioning as in, at the base of the tank or above the tapping point at some easily accessable location. In my experience, mounting the transmitter sensor level with the tapping point for connection for the sensor is by far the most reliable and accurate. Even if this location is less accessable than higher up, the increased reliability will mean you don't need to access it again. Trust me, been there, done it for 50 yrs.
 
greeny said:
In the industrial world of level measurement you have a choice of dry leg or wet leg measurement and the option of sensor positioning as in, at the base of the tank or above the tapping point at some easily accessable location. In my experience, mounting the transmitter sensor level with the tapping point for connection for the sensor is by far the most reliable and accurate. Even if this location is less accessable than higher up, the increased reliability will mean you don't need to access it again. Trust me, been there, done it for 50 yrs.
Click to expand...
my only concern is that we are talking a 1200lt diesel tank (granted it's rarely above 700lt but still a lot of diesel)
IF something silly happens while I'm away, I'll be pumping all that lot in the sea through the e/r bilge pump which is not nice.
That's the only reason for considering the top sensor approach...
 
Vas,

increasing pressure air volume diminishes.
Try this: bottle with little water – two glasses -, insert sensor hose as you did, hold hose firm, mark level of water in the hose. Fill the bottle, check again the level in the hose.

Rgarside,

I think all is correct in the attachment. But the “Head” is the distance h - l.
What we need is the pressure as a function of h, and l varies with pressure.
I am trying to obtain how l varies but it’s a long way and to night it’s too late.

You too could do it if you have time.
I'll report if I succeed.

Cheers

Sandro
 
vas said:
my only concern is that we are talking a 1200lt diesel tank (granted it's rarely above 700lt but still a lot of diesel)
IF something silly happens while I'm away, I'll be pumping all that lot in the sea through the e/r bilge pump which is not nice.
That's the only reason for considering the top sensor approach...
Click to expand...

Use quality fittings and pipe made off correctly and there should be minimal risk of leaks. Even if you mount the sensor above tank level there will be a connection at the base of the tank for the sensor take off. The main take off to the engine must be down at that level, do you worry about that leaking? Even if a leak ensued it is more likely to be a weep/drip and not a catastrophic failure resulting in 1200ltrs in the bilge.
Sometimes we overthink these things and just need to keep it simple.
You should always fit at valve at the tapping point for maintenance and maybe to close when you're away, but then of course you're adding more fittings and more potential for leaks.
Note to self, stop overthinking it.
 
Sandro said:
Rgarside,

I think all is correct in the attachment. But the “Head” is the distance h - l.
What we need is the pressure as a function of h, and l varies with pressure.
I am trying to obtain how l varies but it’s a long way and to night it’s too late.
Click to expand...

In my sketch, h [head] is the level of liquid in the tank. The results and plot show the air pressure in the tube as a function of the level of liquid in the tank. I have ignored temperature effects, leaks and gas diffusion/absorption. One way to eliminate those concerns is to use the well known Pneumopress approach, where you pump some air down the tube first, so that the level of liquid in it is at its lowest point.
 
rgarside said:
In my sketch, h [head] is the level of liquid in the tank. The results and plot show the air pressure in the tube as a function of the level of liquid in the tank. I have ignored temperature effects, leaks and gas diffusion/absorption. One way to eliminate those concerns is to use the well known Pneumopress approach, where you pump some air down the tube first, so that the level of liquid in it is at its lowest point.
Click to expand...

I completely agree that if, by Pneumopress, you push the water level in the tube down to its starting position, the pressure in the tube (and in transducer on top of it) is equal to the pressure at the bottom of the tank, thus giving an exact measure of head from water level to tank bottom.
But if, filling the tank, the water level in the tube is allowed to raise - as it will do -, the pressure measured is that at this level, lesser than the correct bottom pressure by the water head from bottom to the level in the tube, l in your sketch.

In your attachment - an Excell leaf I suppose - one can not see calculations. May be the variation of l is already taken into account.

I am trying to work out the whole matter but things don't yet square.
If and then I can give something clear I'll report.

Sandro
 
Sandro said:
But if, filling the tank, the water level in the tube is allowed to raise - as it will do -, the pressure measured is that at this level, lesser than the correct bottom pressure by the water head from bottom to the level in the tube, l in your sketch.
Click to expand...

Sandro,

I still don't understand why if you have the sender plugged in at the top of the tube, filling the tank the water level will rise.
Of course if the tube is open, water will rise, but that's not the point imho.

cheers

V.
 
I am mostly with Greeny. Installing and calibrating pressure transducers on tanks is an important part of my day job of installing automation systems. Some things i have learned.
  • in the dip tube type system, over time air will dissolve into the liquid and mess up the calibration hence the wide use of bubbler type systems Bubbler Tube System for Level Measurement – Operating Principle. The downside is the accuracy limitation. Often used for "near enough" level measurement for flammable and combustible liquids as the transducer itself can be placed outside the hazardous zone.
  • Google Bubbler level transducer.
  • In some applications i have used a submersible pressure transducer. These put a water proof transducer down inside the tank and hanging from its own cable. The cable includes a really small breather tube for the air side of the diaphragm. These can be installed in a stilling tube so they don't slosh around.
  • Best Accuracy is a pressure transducer at the bottom exterior of the tank.
    • You should always use an isolating valve on any tank fitting.
    • Don't install an elbow so as to be able to screw the transducer in vertically. If there is liquid in the elbow and the valve to the tank is shut, as you screw in the transducer you can generate hydraulic pressure in excess of the transducers diaphram rating.
    • For similar reason, don't shut the valve to the transducer and go home. The heat of the next day can generate thermal expansion in the trapped liquid that can destroy the instrument.
      • NB, commercial units generally have an overpressure rating that is huge in comparison with the measurement range. Even when the diaphragm is damaged by overpressure, they are unlikely to actually leak.
And as for anything, you generally get what you pay for! Pressure transducers essentially are a strain gauge attached to a diaphragm and the pressure causes minute changes in resistance. Temperature also causes changes in resistance. Different diaphragm materials also affect linearity. So Industrial units are physically robust and give a linear result over wide temperature ranges - at a cost.
 
thanks for the Bubbler tube system pointer JtK, too complicated for a boat tank tbh.
Plan to tee off the stop cock at the bottom of the tank going to the open top sight gauge tube and add my pressure sensor at the bottom there.
Just have to remember that off season, boat going nowhere, I can close that stop cock and there wont be any cause for concern

V.
 
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Right answer Vas. All the previous controversy and conjecture is eactly why I recommended that method in the first place, as would any other industrial instrumentation engineer.
 
Sandro said:
In your attachment - an Excell leaf I suppose - one can not see calculations. May be the variation of l is already taken into account.
Click to expand...

See post #18 - the values in the attachment are the results of solving the simultaneous equations that include the height the liquid rises in the tube, denoted as "l" in the sketch.
 
ok guys, how do i wire this up

hsc-series-ssc-series-installation-instructions-50044171-f-en.pdf - sorry don't seem to be able to set up a link :(
page 9
bottom dual sensor = SIP AA: Dual axial barbed ports, opposite sides
4 pins, can work out which side is 'front'
page 15 so no 1 pin on the left
2 = supply
3 = ? signal of which side of the sensor
4 = ? signal of which side of the sensor

and is it going to matter which side i connect the water tank outlet too ?
 
Hold it with the labelling print to the front, pins pointing downward and pin 1 is on the left.

Port 1 is the port pointing towards you when you have the device in this orientation and is the connection to your tank or the item you want to measure pressure in.
Port 2 is the reference side and in the case of measuring liquid level in an un pressurised tank it can be left un connected (at atmospheric pressure the same as your water tank).

For the analogue version:-
pin 1 - NC - not connected.
pin 2 - supply voltage
pin 3 - voltage signal out
pin 4 - ground or 0 volts.

This is not a device to measure 2 different presures and give 2 ouputs. It measures the difference between port 1 and port2 and gives an analogue output to show that diffential.
 
vas said:
Sandro,

I still don't understand why if you have the sender plugged in at the top of the tube, filling the tank the water level will rise.
Of course if the tube is open, water will rise, but that's not the point imho.

cheers

V.
Imagine doing this:
We dip the open tube in water in the tank. Levels inside and outside the tube are same level. Pressure at the level is atmospheric pressure. (0 bar relative, 1 bar absolute)
We plug the top of the tube with the sender.
We add water in the tank until 1 m higher. The water pressure in tank at the old level outside and inside the tube is now about 0.1 bar relative, that is 1.1 bar absolute).
Inside the tube the water surface is pushed down by the air at 1 bar and is pushed up by the water at 1.1 bar. What can it do but to raise?
It will raise until air pressure (increasing because of the shrinking volume) reaches the value of the water pressure, which will be some less than at the starting level, having a lesser head. Here we have balance between the two equal pressures.
Do you agree?

If you wish you can carry out the experiment suggested in post #25 and see what happens.

Cheers
Sandro

P.S.
Practically, as others said and as you say in post #32, if you manage to fit a tee and the sender at the output tube at the bottom of the tank every issue is overcome.
Click to expand...
Click to expand...
 
It won't to any great degree. As you fill the tank the head pressure will cause the "air" in the tube to compress slightly. Thus the level in the tube will rise slightly. If yo want to do it this way then you need to set it up with an empty tank to start with then fill it up. If you ever take off the tube at a later time and the tank is part full you will have problems setting it up again .
Why bother! Keep it simple. I'll say it for the last time, put the sensor at the bottom.
I'm out of here.
 
greeny said:
It won't to any great degree. As you fill the tank the head pressure will cause the "air" in the tube to compress slightly. Thus the level in the tube will rise slightly. If yo want to do it this way then you need to set it up with an empty tank to start with then fill it up. If you ever take off the tube at a later time and the tank is part full you will have problems setting it up again .
Why bother! Keep it simple. I'll say it for the last time, put the sensor at the bottom.
I'm out of here.
Click to expand...

Completely agreed.
It's up to everyone to judge how much "slightly" is suited to his own application.

Cheers
Sandro
 
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