Are you fooling yourself?
The capacitance increase will only be one puff per cm.

Colin55 If you mean 1 pF it could be a lot more sensitive than that! Anyhow very small values of capacitance change is ok for heterodyne sampling or bridge sampling circuit. Just as long as error margins are kept to minimum!

If you want accurate measurement, get a washing machine float from the tip.

colin55 I suppose that would work so would washer fill diaphragm (which basically just weighs column of water) but I say capacitance method is less hassle cuz it needs only one small part to be safe for contact with potable water.

 

You can do it with a pressure tube and no parts are exposed to the water.
A pressure tube gives you a multiplication-factor.
"If you mean 1 pF it could be a lot more sensitive than that!"
HOW ???????
I have made caps out of twisted wires for the past 40 years. It is about 1p per cm. And your arrangement will be a lot less than 1p per cm.

 

suppose that would work so would washer fill diaphragm (which basically just weighs column of water)

You can do it with a pressure tube and no parts are exposed to the water.
A pressure tube gives you a multiplication-factor.

I like it!

Colin55 If you mean 1 pF it could be a lot more sensitive than that!

"If you mean 1 pF it could be a lot more sensitive than that!"
HOW ???????

In all fairness to @Aleph(0) , electronic calipers work on a similar principal (the details of which I ignore)-- The 'trick', perhaps, is in maximizing 'interface' area?

Best regards
HP

 

In all fairness to @Aleph(0) , electronic calipers work on a similar principal

What you are saying is This:
"In all fairness to @Aleph(0) , electronic calipers work on a similar head-master"

Put the calipers in the water if you think the concept is so wonderful.

 

What you are saying is This:
"In all fairness to @Aleph(0) , electronic calipers work on a similar head-master"

Tut! Tut!! Tut!!! -- The 'politic' title is 'Head Teacher' Golly! I've been usage corrected and microaggressed in a single sentence! -- Now I seem to have misplaced my Crayolas just when my need is nearest me! Wadda world!

Put the calipers in the water if you think the concept is so wonderful.

Feeling a bit 'owley' are we? -- My reference to electronic calipers was merely by way of an example of electrostatic metrics - again, I ignore the details, so my comment may be irrelevant after all - but there it is...

Slinking off to my safe space...

TTFN
HP

 

electronic calipers work on a similar principal

Are you sure about that? The ones I'm familiar with and have, work on a "magnetic tape" like principle. Like a piece of recording tape with a varying magnetic strength. The ones before that were optical, a glass strip with etched lines in it. But then again mine are old. Like me.

 

Are you sure about that? The ones I'm familiar with and have, work on a "magnetic tape" like principle. Like a piece of recording tape with a varying magnetic strength. The ones before that were optical, a glass strip with etched lines in it. But then again mine are old. Like me.

FWIW HERE'S a discussion of calipers employing 'the electrostatic metering scheme' - though I'm bound to say magnetic and optical encoding (as described in your post) would likely achieve greater stability

But then again mine are old.

'Blasphemous' tho it may be, it has long been my observation that 'retro technology' often equals superior technology -- Sadly, 'cheaper' sells without regard to quality

Very best regards
HP

 

The Inductosysn system was used for many years, in fact still is in some areas.

https://www.google.ca/url?sa=t&rct=...MzREx30rg&sig2=cXGnRNmHRNgXNpjtq81osQ&cad=rja
Max.

 

The question of the second conductor will be raised over and over by people like myself and Nick Bacon until someone points out just where this thing is conected in this scheme. OK, you can count the inner conductor as the wire, and the insulating jacket as the dielectric. However, you cannot define/use/guess the water itself is the second conductor until you tie the water back into your circuit.

This requires some mechanism. Some piece of metal perhaps. Something more substantial than a wave of the hand.

As far as being more expensive than an ultrasonic solution, they are probably evenly matched, especially in the controlling electronics.

Capacitive requires a single invasive connection for a rod assembly (two rods separated by the liquid, as has been used countless times) which can be an extension of a standard threaded pipe connector.

Ultrasonic needs one or two openings plus a port opening, plus some sort of protection for liquid egress. Ultrasonic may be done thru a vessel wall but required a much higher crystal frequency (1-3 MHz) to go thru the bottom of the vessel itself.

Do note I have worked on both types. The ultrasonic ones were definitely more interesting as service calls entailed a trip to a boatyard, security clearances, and a long 3 story climb down a ladder to the bottom deck of a Virginia class submarine.

 

The question of the second conductor will be raised over and over by people like myself and Nick Bacon until someone points out just where this thing is conected in this scheme. OK, you can count the inner conductor as the wire, and the insulating jacket as the dielectric. However, you cannot define/use/guess the water itself is the second conductor until you tie the water back into your circuit.

You raise an interesting point! -- Inasmuch as such systems are demonstrably viable, it would seem a matter of capacitive loading (i.e. 'return' by omni/multi-path E-field 'coupling'), as it were?... Definitely worthy of some experimentation!

Best regards
HP

 

The Inductosysn system was used for many years, in fact still is in some areas.

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiwrtG97Z7RAhVG6IMKHRf0D0QQFggjMAA&url=http://measure.feld.cvut.cz/en/system/files/files/en/education/courses/xe38szp/02-Position-c_0.pdf&usg=AFQjCNEkA6Ag6jT6UGSlDntV4MzREx30rg&sig2=cXGnRNmHRNgXNpjtq81osQ&cad=rja
Max.

Interesting! -- FWIW I find it reminiscent of the scheme employed by certian old 'drafting tablets'?

Best regards
HP

 

One must be careful with making a selection. Wire insulations often contain plasticizers, and lubricants including lead and other ROHS banned chemicals that are nasty if not dangerous. Even metals, brass for example, can be deceiving because they may be alloyed with lead.

 

Inasmuch as such systems are demonstrably viable, it would seem a matter of capacitive loading (i.e. 'return' by omni/multi-path E-field 'coupling')

HP that's right! It's really just variable surface area _antenna_!

Slinking off to my safe space..

HP I say while you're there you should resurrect EHT tutorial!

 

HP that's right! It's really just variable surface area _antenna_!

Or, more precisely, a variable surface area interface - hence, in effect, variable capacitive loading via a variable coupling

Best regards
HP

 

The question of the second conductor will be raised over and over by people like myself and Nick Bacon until someone points out just where this thing is connected in this scheme. OK, you can count the inner conductor as the wire, and the insulating jacket as the dielectric. However, you cannot define/use/guess the water itself is the second conductor until you tie the water back into your circuit.

Let me reassure that there is a conductor to connect water back to the circuit.

Probe 1. This is the insulated wire. Its end is sealed or taken out of water so is not in direct contact with water.

Dielectric mediums: The Insulating material around the wire that is used for the probe. (this is in contact with water)

Probe 2. This is the bare ligature wire (or any suitable stainless steel that is safe in drinking water) wrapped around a stiff rod (pvc pipe for this case). Water is in contact with this wire.

 

The arrangement :

 

It is easier and cheaper to use ultrasonics. The Tx / Rx is only $2.00

I have tried to use ultrasonic distance sensor (waterproof sensor from eaby). But it seems to be giving readings from the surrounding walls and base. For a moment I thought it penetrated water and did not sense the water level at all. My conclusion is that ultrasonic sensors does not work.

HP I say it's possible any polar liquid will work even without electrolytes ?

Electricity passes through the water that I am going to sense the level of. So I guess its conductive. But may not work for distilled water.

You can do it with a pressure tube and no parts are exposed to the water.

The tanks of which I am going to measure the water is about 25ft above ground. So I have to match its pressure for the pressure tube to work, right?

Alternatively considering a pressure gauge, If it would work, this would be the simplest method to measure water level. Also not having to climb up to the water tank . Get a pressure traducer, just plug in to a pipe line and whoa!.... (well would it be that simple). My guess is that it would be interfered as the taps open and close. Due to the surge pressure (water hammer) the reading would keep varying or at least oscillate until the wave subsidies. Other problem is to get a low pressure (15 psi pressure sensor)

One must be careful with making a selection. Wire insulations often contain plasticizers, and lubricants including lead and other ROHS banned chemicals that are nasty if not dangerous. Even metals, brass for example, can be deceiving because they may be alloyed with lead.

You are back to the point. This is what I was afraid of. I wanted to put a wire into drinking water. So is the wire “clean” enough for it. Clean in the sense, no harmful substance and chemicals that would leak during long term use.

 

Other problem is to get a low pressure (15 psi pressure sensor)

The water level sensor in a clothes washer is designed for only 2 or 3 feet of water pressure. That resembles 1.5 PSI. The sensor tube is normally filled with atmospheric air. That air transmits the pressure to the diaphragm without loss, but air is compressible, so some water does go up the sensor tube. You are not required to immerse the sensor tube in the water. It will sense if only air pressure is available. If you only need to detect water in the top 3 feet of the tank, you can use a clothes washer sensor without any modification. The output is a simple "click" switch.

The usual method of adjustment is a spring pressing against the top of the diaphragm. The adjustment in a clothes washer is a cam which pushes the spring by different amounts, depending on how far you turn the knob. I might say you can increase the range by using a stronger spring, but that depends on the internal structure. If the diaphragm is limited in downward movement by a mechanical stop, you can not break the diaphragm by increasing the spring pressure. If the diaphragm has no mechanical stop, I fear you might break it by trying to get it to sense with a 15 PSI spring. All this is moot if you only need to sense the top 3 feet of water.

 

I have used a pressure transmitter from USA Bluebook SKU 16295 for $111.00. I purchased this unit when my Pressure differential gauge was being repaired for $800.00. You can use any senor range above the level you are trying to read. The closer the scale is to you target height, the more accurate your readings will be.

 

I maybe missing something in this, wouldn't be the first time. If this is just for a water level for a drinking water system, why do you need to know all of the levels? Wouldn't a high level to shut the pump off, and a low level to turn the pump on, be enough? And the easiest and least expensive way would to be to use two automotive coolant level sensors. Drill and tap a hole at both levels and insert the sensor and wire them up. Just the first one I came across that looked like it would work - http://www.fozmula.com/product/capacitance-liquid-level-switch-s87/