Admittance level sensor principle

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seyyah

Joined: 07 Oct 2001
Posts: 578
Helped: 1

30 May 2009 16:55 admittance level measurement

I could not find enough information about this subject. This technology looks like the capacitive sensing tecnology but they say that it measures the resistance along with the capacitance and make some extractions to prevent false measurement etc. How can i find deep information about this subject, the principle etc. Thanks.

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FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

30 May 2009 17:33 r.f. admittance level measurement

I guess, you won't find much. The technique is pure empirical to my opinion. It depends on the electrode design (e.g. if the sensor uses insulated electrodes) and the sensed media's (typically a liquid) dielectric properties. Some relations can be easily predicted from general knowledge and technical tables of material properties, others have to be evaluated in practical tests. You may find some information in handbooks of industrial measurement or respective IEEE transactions and professional journals, but I don't expect much from this sources.

Or try to learn from commercial products that claim to use admittance sensing.

seyyah

Joined: 07 Oct 2001
Posts: 578
Helped: 1

02 Jun 2009 20:57 level sensor working principle

FvM wrote:

Does this use multiple electrodes according to your opinion?

PLCMentor.com

Joined: 26 Mar 2009
Posts: 23
Location: North Carolina, USA

03 Jun 2009 17:14 level admittance

There is usually just one probe. The circuit consists of a probe and is completed by the vessel wall. If the vessel is not conductive, then a conductive material must be inserted to complete the circuit. So in essence for most applications, the vessel could be thought of as a second electrode. I found this page with a quick search that you might find interesting:

http://www.omega.com/literature/transactions/volume4/T9904-13-RF-CAP.html

Russell
www.PLCMentor.com

seyyah

Joined: 07 Oct 2001
Posts: 578
Helped: 1

03 Jun 2009 20:39 working principle of level sensor

Hi, thanks but that page does not tell the difference between the capacitive and the admittance sensor.

PLCMentor.com

Joined: 26 Mar 2009
Posts: 23
Location: North Carolina, USA

03 Jun 2009 20:46 capacitor sensor principle

I would assume from the first line of the page that there is no difference. I quote:

"Capacitance level detectors are also referred to as radio frequency (RF) or admittance level sensors."

Russell
www.PLCMentor.com

wh00per

Joined: 14 Jul 2009
Posts: 12
Location: Canada

14 Jul 2009 17:50 capacitive sensor principle

Defining Terms
Admittance (Y): The reciprocal of impedance.
Immittance: A response function for which one variable is a voltage and the other a current. Immittance is a general term for both impedance and admittance, used where the distinction is irrelevant.
Impedance (Z): The ratio of the phasor equivalent of a steady-state sine-wave voltage to the phasor equivalent of a steady-state sine-wave current. The real part is the resistance, the imaginary part is the reactance.

Now, let's give an example on Aluminum Oxide Sensors. The sensors are formed when a layer of porous, moisture sensitized aluminum oxide is deposited on a conductive substrate and the oxide is coated with gold. The technology has been refined to take advantage of semiconductor manufacturing techniques and higher purity substrates (such as ceramic) to produce sensors with consistent responses to moisture changes in the oxide.

A typical aluminum oxide sensor is in essence a capacitor. The conductive base and the gold layer become the capacitor’s electrodes, forming what is essentially an aluminum oxide capacitor. Water vapor penetrates the gold layer and is absorbed by the porous oxide layer. The number of water molecules absorbed determines the electrical impedance of the capacitor. For example, aluminum oxide hygrometers respond to the vapor pressure of water over a very wide range of vapor pressures. The strong affinity of water for this oxide, combined with the large dielectric constant of water, makes this device highly selective toward water. It does not respond to most other common gases or to numerous organic gases and liquids.

In situations in which aluminum can be chemically attacked, silicon sensors with a tantalum metal base could be used as an alternative. Such sensors are the most inert, although their sensitivity is somewhat less. The oxide layer is generally described in the form of a mass of tubular pores running up from the metal base to the exposed surface. Change in the size of these tubules with time is presumed to be the cause of the slow shifts in calibration often experienced with these sensors. Water is absorbed in these tubules in amounts directly related to the moisture content of the gas in contact with it. The amount of water is sensed electrically by measuring the change in capacitance and/or admittance produced by this water. Because of the radius of the pores in the aluminum oxide, the sensor is virtually specific for water molecules.

So, if you measure capacitance with the sensor electronics .. you have a capacitive probe, if you measure admittance (the reciprocal of impedance) you have an admittance probe, if you measure both, you have a hybrid ..

Hope it helps ..

seyyah

Joined: 07 Oct 2001
Posts: 578
Helped: 1

13 Sep 2009 23:13 admittance probe

I have several ideas how to measure a capacitance but no clear idea of admittance or impedance or resistance? Do you know how?

kender

Joined: 19 Jun 2005
Posts: 1231
Helped: 88
Location: Stanford, SF Bay Peninsula, California, Earth, Solar System, Milky Way

14 Sep 2009 3:52 level sensor princip

seyyah wrote:

I have several ideas how to measure a capacitance but no clear idea of admittance or impedance or resistance? Do you know how?

If amplitude and phase have been measured, then both real and imaginary components of impedance can be calculated. Suppose, you know them, how are you planning to use them?

seyyah

Joined: 07 Oct 2001
Posts: 578
Helped: 1

14 Sep 2009 21:25 insulated water level detector

kender wrote:

seyyah wrote:

I have several ideas how to measure a capacitance but no clear idea of admittance or impedance or resistance? Do you know how?

If amplitude and phase have been measured, then both real and imaginary components of impedance can be calculated. Suppose, you know them, how are you planning to use them?

I think it would be difficult to measure the amplitude and phase of both the current and the voltage at RF frequency. I believe there is another way. Because the real values may not be needed only some proper and proportional values related to the measurement result. For example in a capacitive measurement, not the real capacitance is calculated but some relative values to capacitance are measured like the frequency or charge time etc.