Porous medium sensor
A porous medium sensor apparatus includes a sensing portion at least partially insertable in the porous medium. The sensing portion has a housing with a gas exchange aperture defined therein and a water-repellant membrane mounted in the gas exchange aperture, the water-repellant membrane preventing water communication through the gas exchange aperture. The sensing portion also has a parameter sensor mounted in the housing for measuring a parameter of the porous medium in which the sensing portion is inserted.
1. A porous medium sensor apparatus comprising: a sensing portion at least partially insertable into a porous medium, the sensing portion having a housing with an outer wall and a gas exchange aperture extending through the outer wall in a section in contact with the porous medium when the sensing portion is at least partially inserted therein and a water-repellent membrane mounted to the gas exchange aperture, the water-repellent membrane preventing water communication through the gas exchange aperture; and a parameter sensor mounted in the housing for measuring a parameter of the porous medium in which the sensing portion is inserted.
2. The porous medium sensor apparatus as claimed in claim 1 , wherein the sensing portion comprises an internal chamber in gas communication with the porous medium in which the sensing portion is at least partially inserted through the water repellent membrane.
3. The porous medium sensor apparatus as claimed in claim 1 , wherein the water repellent membrane is in direct gas communication with a port of the parameter sensor and is porous and gas permeable.
4. The porous medium sensor apparatus as claimed in claim 1 , wherein the water repellent membrane has a first face contacting the porous medium when the sensing portion is at least partially inserted therein and a second face, opposed to the first face and extending in the housing, gas pressures on the first and the second faces of the water repellent membrane being substantially equal.
5. The porous medium sensor apparatus as claimed in claim 1 , wherein the water repellent membrane comprises a material selected from a group consisting of: porous hydrophobic polypropylene and porous hydrophobic polyethylene.
6. The porous medium sensor apparatus as claimed in claim 1 , wherein the sensing portion comprises a matrix water potential sensing portion and the parameter sensor comprises a pressure sensor having a first port in fluid communication with the porous medium and providing an indication of liquid pressure in the porous medium and a second port in gas communication with the water membrane and providing an indication of atmospheric gas pressure.
7. The porous medium sensor apparatus as claimed in claim 6 , wherein the second port and the water repellent membrane are in gas communication through a gas channel extending in the housing.
8. The porous medium sensor apparatus as claimed in claim 1 , wherein the parameter sensor is selected from a group consisting of: an electrical transducer, a pressure sensor, a H+-selective transducer, an ion-selective transducer, a temperature sensor, a humidity sensor, a liquid sensor, and a gas sensor.
9. The porous medium sensor apparatus as claimed in claim 1 , wherein the water-repellent membrane prevents water infiltration in the housing through the gas exchange aperture and allows gas communication between atmosphere and the housing through the porous medium; the porous medium sensor apparatus further comprising:
a porous tip mounted to the housing, insertable into the porous medium simultaneously with the housing, having pores fillable with liquid solution, and the pores being in gas communication with the housing through a one-way flow control member, gas communication between the porous tip and atmosphere being allowed via the one-way flow control member and the water-repellent membrane; and wherein
the parameter sensor measures a quantity in said liquid solution, the pores of the porous tip being in fluid communication with the sensor, said quantity being representative of said parameter in said porous medium.
10. The porous medium sensor apparatus as claimed in claim 9 , wherein the housing comprises an internal chamber, the water-repellent membrane preventing water infiltration in the internal chamber through the gas exchange aperture and allowing gas communication between atmosphere and the internal chamber, the pores of the porous tip being in gas communication with the internal chamber through the one-way flow control member.
11. The porous medium sensor apparatus as claimed in claim 9 , wherein the housing comprises a gas exchange channel having a first port connected to the one-way flow control member and a second port connected to the water-repellent membrane, the water-repellent membrane preventing water infiltration in the gas exchange channel through the gas exchange aperture and allowing gas communication between the porous medium and the gas exchange channel, the pores of the porous tip being in gas communication with the gas exchange channel through the one-way flow control member.
12. The porous medium sensor apparatus as claimed in claim 1 , wherein:
the water-repellent membrane covers the gas exchange aperture, prevents water infiltration in the housing therethrough, and allows gas communication with atmosphere through the porous medium; and
the parameter sensor has a reference port in gas communication with the water-repellent membrane.
13. The porous medium sensor apparatus as claimed in claim 12 , wherein the water-repellent membrane is porous and gas permeable and inserted into the porous medium when the housing is inserted therein.
14. The porous medium sensor apparatus as claimed in claims 12 , wherein the parameter sensor comprises a pressure sensor having a first port in fluid communication with the porous medium and providing an indication of liquid pressure in the porous medium and a second port in gas communication with the water-repellent membrane and providing an indication of atmospheric gas pressure, the second port and the water-repellent membrane being in fluid communication through a liquid free chamber defined in the housing.
15. The porous medium sensor apparatus as claimed in claim 1 wherein the parameter sensor comprises:
a pressure sensor mounted in the housing and having a reference port in gas communication with atmosphere through the water repellent membrane, a liquid port in fluid communication with the porous medium when the housing is inserted therein, the pressure sensor providing an indication of a matrix water potential by comparing liquid pressure in the liquid port and gas pressure in the reference port.
16. The porous medium sensor apparatus as claimed in claim 15 , wherein the sensing portion comprises an internal chamber in gas communication with the porous medium in which the sensing portion is at least partially inserted through the water repellent membrane and in liquid communication with the porous medium in which the sensing portion is at least partially inserted through a porous tip, the water-repellent membrane extending over the gas aperture and preventing water infiltration in the housing.
17. The porous medium sensor apparatus as claimed in claim 1 , wherein
the water-repellent membrane is in direct contact with the porous medium and allows gas communication with atmosphere through the porous medium;
the parameter sensor comprises a pressure sensor mounted in the housing and having a reference port in gas communication with the water-repellent membrane; and
the porous medium sensor apparatus further comprises a porous tip mounted to the housing, insertable into the porous medium simultaneously with the housing, having pores fillable with liquid, and the pores being in fluid communication with the pressure sensor, the pressure sensor providing an indication of the matrix water potential by comparing the pressures in atmosphere through the reference port and in the porous tip.
18. The porous medium sensor apparatus as claimed in claim 1 , wherein the water-repellent membrane is recessed in the gas exchange aperture and spaced-apart from a lateral wall of the housing.
19. The porous medium sensor apparatus as claimed in claim 1 , wherein the water-repellent membrane is in direct contact with the porous medium when the sensing portion is at least partially inserted therein.
20. A porous medium sensor apparatus comprising: a sensing portion at least partially insertable into a porous medium, the sensing portion having a housing with a gas exchange aperture defined therein and a water-repellent membrane mounted to the gas exchange aperture, the water-repellent membrane preventing water communication through the gas exchange; and a cover mounted to the housing and covering the gas exchange aperture, the cover substantially preventing granular material to obstruct the gas exchange aperture while allowing gas communication between atmosphere and the gas exchange aperture; and a parameter sensor mounted in the housing for measuring a parameter of the porous medium in which the sensing portion is inserted.
21. The porous medium sensor apparatus as claimed in claim 20 , wherein the cover comprises a peripheral wall abutting the housing with a tightness substantially preventing granular material to infiltrate in between while allowing gas communication and having a recess defined internally therein in register with the gas exchange aperture.