Process and instrument for moisture measurement

• US 20010030543A1
• Filed: 02/26/2001
• Published: 10/18/2001
• Est. Priority Date: 06/09/1997
• Status: Active Grant

• Current Assignee: University of PUNE (Government of Maharashtra)
• Original Assignee: Kalpana Keshav Joshi, Mahesh Pandurang Abegaonkar, Ravi Narhar Karekar, Rohini Chandrashekhar Aiyer
• Inventors: Karekar, Ravi Narhar, Aiyer, Rohini Chandrashekhar, Abegaonkar, Mahesh Pandurang, Joshi, Kalpana Keshav
• Granted Patent: US 6,407,555 B2
• Time in Patent Office: Days
• US Class Current: 324/643
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 33/025 Fruits or vegetables

Abstract

An instrument and process for measuring moisture content of an article. A microstrip resonator receives a signal from a microwave sweep oscillator. A holder holds the article wherein the article under test is placed over a substrate of the resonator and covers the resonator and provides orientation to the article under test in a desired direction to the sample. A detector receives transmitted as well as reflected signals from a resonator sensor for measurement of Q factor and frequency shift of the resonator. The moisture content of the article is determined by the change in effective permittivity of a cross-section of the miscorstrip.

Claims

1. An instrument for measurement of moisture content of an article such as grains, pulverised samples, fruits, nuts and dry fruits, industrial and food products, comprising

a microwave sweep oscillator,

a source of power supply in the microwave range;

microstrip or resonator means for loading and unloading the article;

microstrip or resonator means for providing orientation to the sample;

a sensor circuit and a detector for measurement of Q factor and frequency shift of the article.

2. An instrument as claimed in

claim 1

, wherein the said means for loading and unloading the article comprises a multilayer microstrip functional hybrid integrated circuits with dielectric overlay.

3. A process for the measurement of moisture content of an article comprising measuring the resonant frequency and quality factor of a microwave microstrip resonator and calculating the shift in the resonant frequency caused by the change in the effective permittivity of the microstrip structure where the change in the resonant frequency is governed by the relation

4. An instrument for measurement of moisture content of a solid and/or a liquid sample such as soil, paper, fruits, single grains, bulk grains, pulverised industrial and agricultural products like flours, soap/detergent powders, chemical fertilizers, sugar syrups and milk products comprising

a sample holder having the sample placed on it covering the entire area of the substrate;

a pulse generating source generating pulse inputs of picosecond resolution, said pulse generating input source being a time domain reflectometer;

microstrip, stripline or coplanar waveguide for measurement of moisture contents connected to the said pulse generating source through a coaxial cable;

means for calibrating the effective permittivity measured against the moisture content of the sample, the said means being microcontroller or a computer or calibrated graphs.

5. An instrument as claimed in

claim 5

, wherein the said sample holder is a microstrip patch covering the entire area of the substrate and extending beyond the end of the conductor and substrate or a sample of a smaller size than that of the length of the said probe.

6. An instrument as claimed in

claim 5

, wherein the said instrument optionally comprises spacer block placed over the said sample for putting pressure on the sample.

7. An instrument as claimed in

claim 6

, wherein the length of the said probe may be varied depending upon the material, dielectric constant of the material and moisture levels to be measured.

8. An instrument as claimed in

claim 7

, wherein the said substrate is a glass, ceramic or polymer or semiconductor substrate, preferably comprising copper gold conductor pattern with optional thin dielectric coating.

9. A process for the measurement of moisture content of a liquid or a solid sample using a time domain reflectometry assembly, comprising

calibrating a time domain reflectometer;

selecting microstripline, stripline or coplanar waveguide probe suitable for the type of sample;

connecting a coaxial cable to the probe;

positioning the sample on a sample holder;

transmitting a pulse signal of the kind used in time domain reflectometry through the coaxial cable;

commencing a measurement of time delay in response to the characteristic reference reflection;

calculating effective permittivity based on the time delay and

calibrating effective permittivity against moisture with optional electromagnetic software and a dedicated microcontroller or a computer or with calibration graphs and tables.

10. A process for the measurement of moisture content of a liquid or a solid sample as claimed in

claim 9

, wherein the said time domain reflectometer generates the pulse of picosecond duration.

11. A process for the measurement of moisture content of a liquid or a solid sample as claimed in claims 9 and 10, wherein the said sample is placed on a microstrip patch covering the entire area of the substrate and extending beyond the end of the conductor and substrate or substrate of smaller size than that of the length of the said resonator.

12. A process for the measurement of moisture content of a liquid or a solid sample as claimed in claims 9, 10 and 11 wherein to remove the air gap the said sample is optionally kept under a spacer block having permittivity of approximately 1.