DMM600 Duff Moisture Meter
6.3 Performance
Accuracy:
±
5% full scale range
Resolution:
1% volumetric water content
7. Operation
The DMM600 is cylindrically shaped with a sample chamber on one end and a
display on the other. Electronics for the water content measurement and serial
communications with a PC are housed in the central part of the cylinder.
7.1 Sample Chamber
The sample chamber holds the sample during measurement. The sample
chamber is accessed by loosening the chamber access thumbscrew, rotating the
sample chamber cap slightly counter-clockwise and lifting the cap away from
the sample chamber.
A piston located inside the cap is attached to the compression knob by a
threaded shaft. With the sample in the sample chamber, the compression knob
is turned to compress the sample for measurement. The knob is also used to
relax the sample for removal.
The bottom of the sample chamber is a printed circuit board containing a
waveguide attached to piston. A high frequency signal is coupled to the
waveguide from the electronics in the main cylinder. The presence of water in
the sample determines the response of the circuit which is converted to water
content using a calibration equation. The waveguide is attached to a piston
which moves against precision springs to obtain correct compression of
sample.
7.2 Electronics
The electronics for the measurement are located below the sample chamber.
The electronics for display and serial communications are located behind the
display.
7.3 Display End
7.3.1 Power Switch
A toggle switch that turns the DMM600 on and off is on the bottom of the
DMM600 next to the display. When the switch is toggled on, a single beep
indicates the DMM600 is turned on. To conserve battery power, the DMM600
will automatically turn off after about 5 minutes of inactivity. If the DMM600
is in the power-saving mode, toggling the power switch or compressing the
sample will restore the measurement mode.
7.3.2 Audible Indicator
The audible indicator uses a port to the side of the power switch.
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