IE83391B1 - A moisture meter - Google Patents
A moisture meterInfo
- Publication number
- IE83391B1 IE83391B1 IE2002/0491A IE20020491A IE83391B1 IE 83391 B1 IE83391 B1 IE 83391B1 IE 2002/0491 A IE2002/0491 A IE 2002/0491A IE 20020491 A IE20020491 A IE 20020491A IE 83391 B1 IE83391 B1 IE 83391B1
- Authority
- IE
- Ireland
- Prior art keywords
- moisture
- moisture meter
- control circuit
- digital control
- meter
- Prior art date
Links
- 239000000463 material Substances 0.000 claims description 19
- 238000005259 measurement Methods 0.000 claims description 9
- 230000004044 response Effects 0.000 claims description 5
- 230000003213 activating Effects 0.000 claims description 4
- 239000011343 solid material Substances 0.000 claims description 2
- 239000000523 sample Substances 0.000 description 7
- 239000002023 wood Substances 0.000 description 6
- 239000011449 brick Substances 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 239000011505 plaster Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000001419 dependent Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 230000003252 repetitive Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 230000001702 transmitter Effects 0.000 description 1
Description
A moisture meter
INTRODUCTION
Field of the Invention
The invention relates to a moisture meter.
Prior Art Discussion
Our prior published British Patent Application No. GB2347220A describes a
moisture meter which has a digital control circuit driving an LED output display.
This meter has many advantageous features such as storage of readings and upload
to a host computer, and choice of a range of different materials having different
response characteristics.
In using a moisture meter for surveying a building it is desirable to hold the meter or
probe against a wall or other surface and to move it across the surface. In this way
the surveyor can see the trend in moisture readings as the meter moves from a dry to
a wet part of a wall or other surface, and can survey the extent of the dampness and
the size of the problem.
Use of a meter of the above type presents problems for surveyors as it is difficult to
track trends on the display as the meter is moved. Very often the surveyor sees
tumbling digits on the display, and not a clearly visible trend.
Another disadvantage of currently available moisture meters is that for some
applications user interaction is complex.
A disadvantage of some analogue moisture meters is that in some applications the
measuring locations are difficult to access and the operator may have to hold the
meter out of sight while taking a measurement. The scale reading may change if the
meter is then moved to a position where the scale can be read.
The invention is therefore directed towards providing a moisture meter to address
these problems.
SUMMARY OF THE INVENTION
According to the invention, there is provided a moisture meter comprising:-
a handheld housing comprising a user input interface, a user output interface
and a moisture sensor for sensing moisture in a solid material upon Contact
with that material;
a digital control circuit comprising means for processing output signals from
said sensor and for generating and storing moisture measurements; and
an output interface comprising a digital to analogue converter (DAC)
connected to the digital control circuit, and an analogue display device
comprising means for providing an analogue moisture display in response to
outputs of the digital to analogue converter.
In one embodiment, the analogue display device comprises a moving coil meter.
In another embodiment, the moisture meter comprises means for linearising
moisture readings.
In a further embodiment, the linearising means comprises a logarithmic amplifier in
the sensor.
In one embodiment, the logarithmic amplifier is connected between a sensor
amplifier and an analogue to digital converter (ADC) of the digital control circuit.
In another embodiment, the digital control circuit comprises an input interface
comprising means for allowing user selection of a desired material.
In a further embodiment, the input interface comprises a user button for selecting a
material.
In one embodiment, the digital control circuit comprises means for generating an
interrupt upon user selection of a material.
In another embodiment, the digital control circuit comprises means for storing a flag
indicating the selected material when the moisture meter is powered down, and for
activating with the same material at power-up.
In a further embodiment, the digital control circuit comprises means for locking to a
current reading in response to user selection of a hold function at the input interface.
In one embodiment, the digital control circuit comprises means for generating an
interrupt upon user selection of the hold function.
In another embodiment, the digital control circuit comprises means for operating in
timed loops of monitoring sensor signals, processing the signals, and outputting a
moisture reading.
In a further embodiment, the digital control circuit comprises means for powering-
down to a sleep mode after expiry of a timeout period for a single reading.
In one embodiment, the digital control circuit comprises means for activating a timer
when a timed processing loop generates the same reading as that for the previous
processing loop, whereby the timeout period is calculated from the time at which a
reading has not changed.
DETAILED DESCRIPTION OF THE INVENTION
Brief Description of the Drawings
The invention will be more clearly understood from the following description of
some embodiments thereof, given by way of example only with reference to the
accompanying drawings in which:-
Fig. l is a front view of a moisture meter of the invention;
Fig. 2 is a schematic diagram showing construction of the meter in more
detail; and
Fig. 3 is a rear perspective view of an alternative moisture meter of the
invention.
Description of the Embodiments
Referring to Fig. l, a moisture meter 1 comprises a hand-held plastics housing 2, an
input interface 3, and a moving coil meter display 4. The meter 1 is shown in more
detail in Fig. 2.
A sensor 10 comprises a transmit electrode 11, a receive electrode 12, a low
frequency generator 13 driving the transmit electrode 11, and a detector/ amplifier 14
connected to the receive electrode 12. Gain switches 15 are used to set the scale, in
this embodiment (1) wood, (2) drywall or roofing, and (3) plaster or brick. Referring
again to Fig. 1 user pressing of a Scale button 20 moves the scale selection between
these three, and an LED 21 is activated to indicate the selection.
Finally, the sensor 10 comprises a logarithmic amplifier 16 which linearises the
sensor output to provide a linear analogue sensor signal to a digital control circuit.
The digital control circuit comprises a PIC microcontroller 17 connected to:-
the Scale button 20, an On button 22, and a Hold button 23,
the LEDs 21,
a DAC (digital to analogue converter) 18, and
a sounder 19.
The DAC 18 drives the moving coil meter 4.
The microcontroller 17 controls/ processes all instrument functions and operations. It
also includes an 8-bit analogue to digital (A/D) converter which converts the
analogue moisture readings obtained from the capacitive sensor/ logarithmic
amplifier chain to digital. As it outputs an 8-bit word, it provides for 256 quantum
steps and hence an accuracy of better than 1%. The digitised readings are
mathematically processed and then outputted as serial data via a two-wire Inter
Integrated Circuit (PC) bus to the digital to analogue (D/A) converter integrated
circuit (IC) 18 which drives the moving coil meter 4 to display the moisture value.
The DAC 18 converts from 8-bit digital back to analogue.
The ON, SCALE and HOLD input ports are configured as interrupt requests, i.e.,
they have priority over all other microcontroller program operations.
Capacitive Moisture Sensor
The two co-planar conductive rubber electrodes 11 and 12 are mounted on the base
of the instrument case. To measure/ detect moisture, the electrodes are lightly
pressed onto the wood or material sample. The capacitance between the electrodes is
governed by the dielectric constant of the wood/ material sample, which is in turn
dependent on the moisture content of the sample. The low frequency generator
circuit provides a constant frequency/ constant amplitude 125 KHz unity mark space
square wave to drive the transmitter electrode which creates an alternating electric
field between the electrodes. This causes a very small AC current flow through the
material sample and into the receiving electrode. An operational amplifier IC
configured as a precision half wave rectifier/ amplifier detects and amplifies the AC
current and outputs a voltage which is proportional to the moisture content of the
sample. The relationship between the moisture content of the sample and the input
current to the detector/ amplifier is exponential and consequently, to maintain a
reasonable balance between detector sensitivity and dynamic range, it is desirable to
alter the amplifier gain to cope with the wide variation in dielectric constant band
between wood, wall and roofing materials. This is achieved by using the gain
switches 15, which are a triple analogue switch IC to set the amplifier gain. The
microcontroller 17 assesses the Scale button 20 input and switches on the gain setting
appropriate to selected scale.
Logarithmic Amplifier 16
The purpose of the logarithmic amplifier 16 is to convert the exponentially
proportional voltage output of the detector/ amplifier 14 to follow a linear
relationship with respect to moisture content. An additional benefit is that the entire
dynamic range of the detector/amplifier 14 can be used, i.e., the measurement range
is increased. Ultimately, this permits the display of the moisture value on the moving
coil meter 4 with an extended linear scale, which provides excellent reading
accuracy.
Illicrocontrollcr I 7
The instrument is powered by a 9 volt PP3 size Alkaline primary battery which
drives a low drop out (LDO), low quiescent current regulator IC to provide a
stabilised 5 volt supply for the microcontroller 17.
In the OFF condition, the
microcontroller 17 goes into a "sleep" mode and in consequence the total supply
current drain is only a few microamps. When the ON button 22 is pressed it
interrupts the "sleep" mode and wakes up the microcontroller 17 which then :-
Switches on the 5 volt supply to all the external circuits.
Starts a timer module on a 2 minute supply timeout sequence.
Checks a battery low voltage detector 25 input and if low (less than 6 volts) issues
a low battery warning by sequentially flashing the three scale LEDs.
Looks up the last use settings for the SCALE button 20 and restores these
conditions, i.e., sets the detector/amplifier 14 gain and switches on the
appropriate LED 21.
Looks up the last use setting for the HOLD button 23. If HOLD was selected,
the LED is put in a flashing mode and the previously saved meter reading is
outputted via the PC bus to the D/ A converter.
Starts a 0.25 second repetitive loop (if not in HOLD) for monitoring and
presentation ofmoisture readings, i.e., A/ D conversion, processing and IZC serial
data output to the D/ A converter.
. Compares current and previous readings every 0.25 seconds. If readings show
change above a preset differential value, the 2 minute supply timeout sequence is
restarted.
. Checks moisture value during each loop and if it exceeds 50 (on the relative
meter scale) commences the audible bleep alarm on the sounder.
. Services any button press (interrupt request) and restarts 2 minute supply timeout
S€q11€I1CC.
. Monitors status of timeout counter, issues double bleep warning at -10 seconds
and, at 0 seconds, closes down all operations and puts microcontroller in "sleep"
mode.
It will be appreciated that the meter 1 has the advantages of digital circuitry such as
the ability to store readings, but can also indicate a moisture trend. The linear output
of the logarithmic amplifier 16 allows all ranges for different materials, to be read on
one linear scale. This avoids the inconvenience of multiple scales and the danger of
taking a reading on a wrong scale.
The digital circuit provides a number of very useful features, including the ability to
store a reading until it can accurately read or recorded, an improved range from 5 to
% moisture content, push button scale selection, and power supply timeout. For
example, range changing can be done by push button instead of a switch. In an
analogue instrument having a number of different scales and a suppressed zero for
timber (5-30%) potentiometers are required to adjust the zero point whereas with the
PIC controller 17 can do this arithmetically.
The advantages of signal storage include, for example the storing and display of the
last reading after a timeout of the power supply, the extending of the timeout period
if the reading changes or a button is pressed. There is also an audible warning of a
high reading.
The advantages include the ability to take measurements at measuring locations
which are difficult to access and the operator may have to hold the meter out of sight
while taking a measurement. The scale reading may change if the meter is then
moved to a position where the scale can be read. With storage of measurements the
hold button can be pressed and the meter moved to a position where the scale can be
read without parallax errors.
It will be appreciated that the meter 1 has a large moving coil meter with a linear
scale for all materials by virtue of the gain switches 15 and the logarithmic amplifier
to linearise capacitive sensor output. The wood moisture measurement range is 5-
%, as compared with a range of 10-20% for prior analogue meters. The three
simple pushbutton controls, ON, SCALE and HOLD allow easy and simple
operation SCALE button selects: (l) Wood/Timber, (2) Drywall/Roofing, (3)
Plaster/ Brick, scales. The three LEDs (light emitting diodes) show the selected
scale, indicate if HOLD is selected, and provide a warning of battery nearing end of
useful life.
selected scale LED flashes to indicate HOLD is in operation. The automatic supply
The HOLD button freezes the moving coil meter reading, and the
timeout (2 minutes) conserves battery life and the supply timeout is automatically
extended if a change in meter reading is detected or if any button is pressed. The
meter 1 also provides a 10 second bleep warning on the sounder 19 prior to end of
the supply timeout period. The last used scale is memorised at supply timeout and is
automatically selected the next time ON button is pressed. If HOLD was selected
prior to supply timeout, the frozen meter reading is digitally memorised and restored
next time ON button is pressed.
Referring to Fig. 3 an alternative moisture meter 30 is illustrated. The meter 30 has
similar processing circuitry, however its housing 31 supports conductive rubber pads
32 and 33, which is turn each support four spring-loaded Contact pins 34. This
contact arrangement is particularly effective for concrete moisture measurement.
The invention is not limited to the embodiments described but may be varied in
construction and detail.
Claims (1)
1. A moisture meter comprising:- a handheld housing comprising a user input interface, a user output interface and a moisture sensor for sensing moisture in a solid material upon contact with that material; a digital control circuit comprising means for processing output signals from said sensor and for generating and storing moisture measurements; and an output interface comprising a digital to analogue converter (DAC) connected to the digital control circuit, and an analogue display device comprising means for providing an analogue moisture display in response to outputs of the digital to analogue converter. A moisture meter as claimed in claim 1, wherein the analogue display device comprises a moving coil meter. A moisture meter as claimed in claims 1 or 2, wherein the moisture meter comprises means for linearising moisture readings. A moisture meter as claimed in claim 3, wherein the linearising means comprises a logarithmic amplifier in the sensor. A moisture meter as claimed in claim 4, wherein the logarithmic amplifier is connected between a sensor amplifier and an analogue to digital converter (ADC) of the digital control circuit. A moisture meter as claimed in any preceding claim, wherein the digital control circuit comprises an input interface comprising means for allowing user selection of a desired material. A moisture meter as claimed in claim 6, wherein the input interface comprises a user button for selecting a material. A moisture meter as claimed in claims 6 or 7, wherein the digital control circuit comprises means for generating an interrupt upon user selection of a material. A moisture meter as claimed in any of claims 6 to 8, wherein the digital control circuit comprises means for storing a flag indicating the selected material when the moisture meter is powered down, and for activating with the same material at power-up. A moisture meter as claimed in any preceding claim, wherein the digital control circuit comprises means for locking to a current reading in response to user selection of a hold function at the input interface. A moisture meter as claimed in claim 10, wherein the digital control circuit comprises means for generating an interrupt upon user selection of the hold function. A moisture meter as claimed in any preceding claim, wherein the digital control circuit comprises means for operating in timed loops of monitoring sensor signals, processing the signals, and outputting a moisture reading. A moisture meter as claimed in any preceding claim, wherein the digital control circuit comprises means for powering-down to a sleep mode after expiry of a timeout period for a single reading. A moisture meter as claimed in claim 13, wherein the digital control circuit comprises means for activating a timer when a timed processing loop generates the same reading as that for the previous processing loop, whereby the timeout period is calculated from the time at which a reading has not changed. A moisture meter substantially as described with reference to the drawings. Llil) indicators sliow:~
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
IE2002/0491A IE83391B1 (en) | 2002-06-17 | A moisture meter |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
IEIRELAND08/03/20022002/0179 | |||
IE20020179 | 2002-03-08 | ||
IE2002/0491A IE83391B1 (en) | 2002-06-17 | A moisture meter |
Publications (2)
Publication Number | Publication Date |
---|---|
IE20020491A1 IE20020491A1 (en) | 2003-09-17 |
IE83391B1 true IE83391B1 (en) | 2004-04-21 |
Family
ID=
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US6747463B2 (en) | Moisture meter | |
US5551159A (en) | Scalable measuring apparatus and displacement display device, system and method | |
US5035064A (en) | Linear measuring devices | |
JP2592387B2 (en) | Tape measure | |
US5832417A (en) | Apparatus and method for an automatic self-calibrating scale | |
US4069716A (en) | Apparatus and method for use in determining conditions related to a plant | |
US7994773B2 (en) | Apparatus and method for in-field magnetic measurements | |
US4879546A (en) | Ultrasonic hand-held refrigerant leak detector | |
EP0979383A1 (en) | Tape measure with manual entry electronic measurement recording feature | |
US6141625A (en) | Viscometer module with crystal resonator-type sensor | |
RU2007101974A (en) | ELECTRONIC DISTANCE MEASUREMENT DEVICE | |
WO1992011529A1 (en) | Material monitoring device | |
US7786449B2 (en) | Device and arrangement for sensing and displaying radiation | |
US4718507A (en) | Electronic scale and length measurement apparatus including a digital readout | |
CA2624947A1 (en) | Hand-held instrument for measuring temperature | |
US4462246A (en) | Percent oxygen gauge | |
US5008665A (en) | Measuring device having transmitter | |
WO1998000683A1 (en) | Pedometer | |
IE83391B1 (en) | A moisture meter | |
IES83002B2 (en) | A moisture meter | |
IE20020491A1 (en) | A moisture meter | |
US20220236440A1 (en) | Apparatus, methods, and techniques of obscured feature detection with live wire detection | |
EP0884578A2 (en) | Portable viscometer with crystal resonator-type sensor | |
GB2172399A (en) | Device for converting cyclic motion into digital output | |
CN210242977U (en) | Measuring device of vibrating wire type sensor |