DMM600 Duff Moisture Meter Revision: 11/12 C o p y r i g h t © 2 0 0 2 - 2 0 1 2 C a m p b e l l S c i e n t i f i c , I n c .
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Table of Contents PDF viewers: These page numbers refer to the printed version of this document. Use the PDF reader bookmarks tab for links to specific sections. 1. Overview......................................................................1 2. Cautionary Statements...............................................1 3. Initial Inspection .........................................................1 3.1 DMM600 Packing List.........................................................................1 4.
Table of Contents 7.7 Drying Samples and Calculating Volumetric Water Content............ 16 7.7.1 Conventional Oven Method ....................................................... 16 7.7.2 Microwave Oven Method........................................................... 16 8. Maintenance ..............................................................17 8.1 8.2 Changing the 9-Volt Battery.............................................................. 17 Cleaning the Sample Chamber ...........................
DMM600 Duff Moisture Meter 1. Overview The DMM600 Duff Moisture Meter is the product of collaboration between Campbell Scientific and USDA-Forest Service, Rocky Mountain Research Station, and Missoula Technology and Development Center. This portable, battery-powered duff meter accurately measures moisture content in duff material, which is critical to those conducting scheduled burns as well as those attempting to battle out-of-control fires.
DMM600 Duff Moisture Meter FIGURE 3-1. Ships with equipment 4. Quickstart This section describes the process for getting a water content measurement. Information about the sensor components, using the software, and calibrating the sensor is located in Section 7, Operation. 1. 2 Unscrew the compression knob completely and loosen (don’t remove) the chamber access thumbscrew. Remove the sample chamber cap by turning slightly counter-clockwise and lifting (see FIGURE 4-1).
DMM600 Duff Moisture Meter Compression Knob Chamber Access Thumbscrew Sample Chamber Cap Chamber Removal Thumbscrew Sample Chamber FIGURE 4-1.
DMM600 Duff Moisture Meter 2. Place duff in the sieve and place the sieve atop the sample chamber (see FIGURE 4-2 and FIGURE 4-3). FIGURE 4-2. Duff placed in sieve FIGURE 4-3.
DMM600 Duff Moisture Meter 3. Finger-work the duff in the sieve until it moves through the sieve and into the sample chamber. The sieve may need to be filled more than once to fill the chamber. The sample should fill the sample chamber to about the beginning of the bevel on the top edge. Don’t overfill the chamber or the compression piston may bind. 4. Remove the sieve.
DMM600 Duff Moisture Meter 6. View the volumetric water content from the display at the bottom of the DMM600 (see FIGURE 4-5). If user calibrations are loaded, the display will toggle between factory and user values. Water content is only displayed while the sample is compressed. Toggle Switch 9-Pin Serial Port FIGURE 4-5. Bottom of DMM600 7. 5. Turn the knob counter-clockwise to stop.
DMM600 Duff Moisture Meter sample is placed in the sample chamber, the lid is attached, and the sample is compressed to a density determined by precision springs. When proper density is reached, an audible indicator sounds and the result is displayed on the readout. Readings are displayed in real time. There is no memory for measurement storage. A standard calibration converts the output of the measurement circuit to volumetric water content.
DMM600 Duff Moisture Meter 6.3 7. Performance Accuracy: ±5% full scale range Resolution: 1% volumetric water content 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.
DMM600 Duff Moisture Meter 7.3.3 Display A two-line, 16-character LCD provides measurement results. When the DMM600 is initially turned on, the display shows: DMM600 Compress sample The following is displayed after the sample is compressed and measured. Std Cal: xx% Freq: xx.xMHz The water content measurement using the standard calibration is listed next to StdCal. The frequency from the measurement circuit is listed next to Freq.
DMM600 Duff Moisture Meter The DMM600 presents water content measurement results in volumetric terms because that is what the DMM600 measures. Conversion to gravimetric requires knowledge of the material bulk density. Bulk density of duff tends to be similar for many forest types. If the bulk density of a particular material is known or measured, the displayed volumetric water content value is easily converted to gravimetric by adjusting the calibration coefficients.
DMM600 Duff Moisture Meter 7.4.1.1 Determining Duff Sample Bulk Density The bulk density of the sample at time of measurement is determined as follows. 1. After the measurement is made, count the number of compression knob rotations required to move compression piston from measurement position to completely out. 2. Use following equation to calculate volume of sample at time of measurement. Volume = 157.97 − 7.25 * rotations 3. Dry then weigh the sample used for the measurement. 4.
DMM600 Duff Moisture Meter FIGURE 7-2. PCDMM user interface display 7.5.2 Calibration Equation The frequency output of the DMM600 is converted to water content using a calibration equation. The response of the DMM600 to changing water content is best described with a quadratic calibration equation. A factory calibration is part of the DMM600 operating system and will always be displayed. The factory calibration to convert frequency (MHz) to volumetric water content is: VolumetricWater Content = 5.
DMM600 Duff Moisture Meter 7.5.3.2 Indicators Three circles provide serial communications information. The left circle indicates which serial communications port is selected. The circle is green when the connection is successfully made. The TX circle is green during transmission from the computer to the DMM600. The RX circle is red during transmission from the DMM600 to the computer. 7.5.3.
DMM600 Duff Moisture Meter DMM600 calibration 70 volumetric water content (%) 60 50 40 30 20 10 0 28 30 32 34 36 38 40 42 frequency (MHz) FIGURE 7-3. DMM600 standard calibration 7.6.2 User Calibration 7.6.2.1 Equipment Required for User Calibration • plastic bags to store samples • a scale to measure sample weight • containers to hold samples for weighing and while drying in oven • a drying oven or microwave to dry samples 7.6.2.
DMM600 Duff Moisture Meter sitting time will allow the water content to equilibrate throughout the sample. 2. Load a portion of the sample into the chamber and take a measurement. See Section 7.4.2, Duff Size and Water Content Heterogeneity, for discussion of sample heterogeneity. Record the frequency in MHz that is displayed as “Raw”. 3. Unscrew the compression knob counting the number of turns from the position of measurement to fully out.
DMM600 Duff Moisture Meter 7.7 Drying Samples and Calculating Volumetric Water Content 7.7.1 Conventional Oven Method For this method a thermostatically controlled oven is required and sample containers suitable for oven temperature of 105°C. Procedure 1. Weigh and record the weight of sample container 2. Place the sample in the container and record the weight of the container and sample. 3.
DMM600 Duff Moisture Meter 6. Return the container with the sample to the oven, and reheat for 1 min. 7. Repeat steps 4 through 6, until the weight does not change. 8. Use the final weight determination in calculating the gravimetric water content.
DMM600 Duff Moisture Meter 18
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