Campbell Scientific CS505 User Manual

CS505 Fuel Moisture Sensor

Revision: 5/08

Copyright © 1998-2008

Campbell Scientific, Inc.

Warranty and Assistance

The CS505 FUEL MOISTURE SENSOR is warranted by CAMPBELL
SCIENTIFIC, INC. to be free from defects in materials and workmanship
under normal use and service for twelve (12) months from date of shipment
unless specified otherwise. Batteries have no warranty. CAMPBELL
SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or
replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
The customer shall assume all costs of removing, reinstalling, and shipping
defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL
SCIENTIFIC, INC. will return such products by surface carrier prepaid. This
warranty shall not apply to any CAMPBELL SCIENTIFIC, INC. products
which have been subjected to modification, misuse, neglect, accidents of
nature, or shipping damage. This warranty is in lieu of all other warranties,
expressed or implied, including warranties of merchantability or fitness for a
particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,
indirect, incidental, or consequential damages.

Products may not be returned without prior authorization. The following
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served by Campbell Scientific, Inc. directly. Affiliate companies handle
repairs for customers within their territories. Please visit
www.campbellsci.com to determine which Campbell Scientific company
serves your country. To obtain a Returned Materials Authorization (RMA),
contact CAMPBELL SCIENTIFIC, INC., phone [phone]. After an
applications engineer determines the nature of the problem, an RMA number
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CAMPBELL SCIENTIFIC, INC.

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Logan, Utah 84321-1784

CAMPBELL SCIENTIFIC, INC. does not accept collect calls.

CS505 Table of Contents

PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.

1. General Description.....................................................1

2. Specifications ..............................................................1

3. Installation....................................................................2

4. Wiring............................................................................4

5. Datalogger Programming............................................4

5.1 CR10X Programming...............................................................................5

5.2 21X Programming ....................................................................................6

5.3 CR1000 Programming..............................................................................7

6. Maintenance.................................................................8

Appendix

A. Explanation of Experimental Data.........................A-1

Figures

3-1. Exploded View of CS505 and CS206 Mounting ....................................3

3-2. CS505 Installation Over Forest Floor, 30cm Over Duff Layer...............3

A-1. Experimental Data Error-Distribution............................................... A-1

Tables

4-1. Wiring for CS505.................................................................................... 4

A-1. Accuracies at Measurement Ranges.................................................. A-2

i

CS505 Fuel Moisture Sensor

1. General Description

The CS505 Fuel Moisture Sensor provides an automated measurement of the
moisture content of a standard 10-hour fuel moisture dowel. The moisture
content of the 10-hour fuel sensor represents the moisture content of small­diameter (10-hour time lag) forest fuels.

Traditionally, the standard fuel moisture stick consists of a rack of four 1/2
inch diameter ponderosa pine dowels. The resulting rack is about 20 inches
long with an oven-dry weight of 100 grams. The characteristic time constant
of the rack is 10 hours. The rack is mounted 12 inches or about 30 centimeters
above the forest floor. The rack is left outside continually exposed to the same
conditions as forest fuels. The rack absorbs and desorbs moisture from its
surroundings. As the rack transfers moisture, its weight changes. Periodic
weighing of the rack determines changes in moisture content and provides an
indication of moisture changes in forest fuels.

The CS505 sensor incorporates the same carefully selected USFS standard
ponderosa dowels as the traditional weighing fuel moisture racks. No artificial
materials (e.g., epoxy sealant) are added to the dowel that would adversely
influence the natural behavior characteristics of the dowel. Because the
complete dowel surface is accessible for moisture exchange, the response of
the CS505 is similar to that of the traditional weighing racks. To optimize
probe-to-probe repeatability and to allow probe interchangeability without
individual calibration, two additional sorts are performed on the dowels before
they are selected to be used as a sensor. First, the dowels are sorted dry by
density to improve accuracy in the dry range of 0 to 15%. Second, the dowels
are sorted after a 50-minute soak by weight to reduce probe-to-probe time
response variation and minimize variability in the wet range of 20 to 50%.

Even after careful selection and sorting is performed to choose the most
representative dowels, the majority of measurement error is due to the
variability of wood. Wood’s ability to transfer moisture is dependent on many
variables, primarily cell structure and wood resin content. These variables
change over time and after repeated wetting and drying cycles. Only a small
amount of overall measurement error is due to the electronic circuitry.

2. Specifications

The fuel moisture sensor consists of two stainless steel strips pressed into
groves in a standard 1/2 inch ponderosa pine dowel and secured with nylon tie
wraps. The probe connects to the electronics with two Phillips head screws.
A shielded four-conductor cable is connected to the circuit board to supply
power, enable the electronics, and monitor the signal output. The printed
circuit board is encapsulated in a waterproof epoxy housing.

High speed electronic components on the circuit board are configured to
oscillate when power is applied. The output of the circuit is connected to the
fuel moisture probe which acts as a wave guide. The oscillation frequency and
therefore output signal of the circuit is dependent on the dielectric constant of

1

CS505 Fuel Moisture Sensor

the media surrounding the stainless steel strips. The dielectric constant is
predominantly dependent on the water content of the wood. Digital circuitry
scales the oscillation frequency to an appropriate rang e for measurement with a
datalogger. The CS505 output is essentially a square wave with an amplitude
of ±2.5 VDC. The frequency of the square wave output ranges from
approximately 600 to 1500 Hz.

*Fuel moisture accuracy:
(with a new stick)
90% of all

measurements rms error

range

0 to 10% ±2% ±1.0%
10 to 20% ±3% ±1.5%
20 to 30% ±5% ±2.2%
30 to 50% ±6% ±2.4%

Range: 0-50%

Power Supply: 9 VDC minimum to

18 VDC maximum

Enable voltage: off at 0 V (<1 VDC)

on at 5 V (>1.5 VDC maximum 12 VDC)

3. Installation

Current usage: 70 mA active/ 10 uA quiescent

Output signal: ±2.5 V square wave with an output frequency of

approximately 600 to 1500 Hz.

Dimensions:
sensor: 1/2 inch dowel, 20 inch long
electronics: 4 x 2.5 x 0.75 inches

*The above accuracy is a static accuracy derived at slow changing conditions
with experimental data.

As shown in Figure 3-1 and Figure 3-2, both the CS505 and CS205 install on
the 10974 mounting stake. The probes install horizontally and should point
south in the northern hemisphere and north in the southern. The rack is
mounted above a representative forest-floor duff layer. The stake is carefully
hammered into the ground so that it is vertical. Don’t hammer on the spot­welded clips that hold the CS505 electronics. Once the stake is installed,
insert the CS505 electronics into the two spring clips. The fuel moisture
sensor (part number 10824) installs on the CS505 electronics with the supplied
Phillips-head screws. The CS205 fuel temperature stick is inserted into the
mounting stake’s compression fitting. The 107 temperature probe is then
inserted into the CS205 stick. Tighten the compression fitting so that it
compresses the split wood and snugly holds the 107 probe.

2

CS505 Fuel Moisture Sensor

The mounting stake ships with a package of 12 ultraviolet light resistant cable
ties. The mounting stake has five holes punched along the edge of the shaft.
There are two pairs of holes higher and one single hole lower on the shaft.
When the stake is inserted into the ground to a depth level with the lower hole,
the probes are at 12 inches or about 30 centimeters above the ground surface.
The two upper pairs of holes are used to attach two tie wraps per cable—one
pair for both the CS505 and CS205/107.

FIGURE 3-1. Exploded View of CS505 and CS205 Mounting

FIGURE 3-2. CS505 Installation Over Forest Floor, 30cm Over Duff Layer

3

CS505 Fuel Moisture Sensor

4. Wiring

Connections to Campbell Scientific dataloggers are given in Table 4-1. When
Short Cut for Windows software is used to create the datalogger program, the
sensor should be wired to the channels shown on the wiring diagram created
by Short Cut.

TABLE 4-1. Wiring for CS505

Color Description

red power 12 V 12 V 12 V 12 V
black ground G G G
green signal Analog Channel Analog Channel Analog Channel Pulse Channel
orange enable Control Port Control Port Control Port Control Port
clear ground

CR800/CR1000/
CR3000

CR10(X)/CR500/
CR510

G

CR23X

21X/CR7

5. Datalogger Programming

This section is for users who write their own datalogger programs. A
datalogger program to measure this sensor can be created using Campbell
Scientific’s Short Cut Program Builder software. You do not need to read this
section to use Short Cut.

The CS505 has a built in enable circuit. When voltage on the enable lead is
less than 1.3 VDC, the sensor is off. When a voltage greater than 1.3 VDC,
commonly 5 VDC, is applied to the enable lead, the sensor is on. The output
signal is a ±2.5 volt square wave. Instruction P27 Period Average in the
CR500, CR510, CR10(X), and CR23X dataloggers measures the frequency of
the square wave with an analog channel.

4

Since fuel moisture doesn’t change very rapidly, the sensor is typically
measured only once an hour.

Instruction P27 measures the period of the output signal in microseconds. To
prepare for the polynomial, the output is scaled by 0.001. A second-order
polynomial is used to convert signal period to percent moisture content with
the following constants:

C0 = -220.14
C1 = 365.89
C2 = -114.96

or, expressed as a second order polynomial
y=-220.14+365.89x-114.96x

2

5.1 CR10X Programming

A program to measure a CS505 fuel moisture sensor using the Period
Averaging instruction P27. P27 is the preferred measurement technique with a
Campbell Scientific, Inc. datalogger. P27 is not an option in the 21X or CR7
datalogger.

;{CR10X}

;CR10X Program for CS505

*Table 1 Program
01: 10.0000 Execution Interval (seconds)

1: If time is (P92)
1: 0 Minutes (Seconds --) into a
2: 60 Interval (same units as above)
3: 30 Then Do

2: Do (P86)
1: 41 Set Port 1 High

3: Period Average (SE) (P27)
1: 1 Reps
2: 4 200 kHz Max Freq @ 2 V Peak to Peak, Period Output
3: 1 SE Channel
4: 10 No. of Cycles
5: 5 Timeout (0.01 sec units)
6: 4 Loc [ PA_uS ]
7: 1 Multiplier
8: 0 Offset

4: Z=X*F (P37)
1: 4 X Loc [ PA_uS ]
2: 0.001 F
3: 3 Z Loc [ FuelM ]

5: Polynomial (P55)
1: 1 Reps
2: 3 X Loc [ FuelM ]
3: 3 F(X) Loc [ FuelM ]
4: -220.14 C0
5: 365.89 C1
6: -114.96 C2
7: 0 C3
8: 0 C4
9: 0 C5

6: Do (P86)
1: 51 Set Port 1 Low

7: End (P95)

CS505 Fuel Moisture Sensor

5

CS505 Fuel Moisture Sensor

5.2 21X Programming

;{21X}

;21X Program for CS505

*Table 1 Program
01: 10.0000 Execution Interval (seconds)

1: If time is (P92)
1: 0 Minutes into a
2: 60 Minute Interval
3: 30 Then Do

2: Do (P86)
1: 41 Set Port 1 High

3: Beginning of Loop (P87)
1: 10 Delay
2: 2 Loop Count

4: End (P95)

5: Pulse (P3)
1: 1 Reps
2: 1 Pulse Input Channel
3: 21 Low Level AC, Output Hz
4: 5 Loc [ FkHz_5 ]
5: 0.001 Multiplier
6: 0 Offset

6: Z=1/X (P42)
1: 5 X Loc [ FkHz_5 ]
2: 4 Z Loc [ PA_uS ]

7: Z=X*F (P37)
1: 4 X Loc [ PA_uS ]
2: 0.001 F
3: 4 Z Loc [ PA_uS ]

8: Z=X*F (P37)
1: 4 X Loc [ PA_uS ]
2: 0.001 F
3: 3 Z Loc [ FuelM ]

A program to measure a CS505 fuel moisture sensor using the Pulse Count
Instruction P3. The fuel moisture sensor is measured when flag 1 is set high.
The measurement is made then flag 1 is set low.

6

9: Polynomial (P55)
1: 1 Reps
2: 3 X Loc [ FuelM ]
3: 3 F(X) Loc [ FuelM ]
4: -220.14 C0
5: 365.89 C1
6: -114.96 C2
7: 0 C3
8: 0 C4
9: 0 C5

10: Do (P86)
1: 51 Set Port 1 Low

11: End (P95)

5.3 CR1000 Programming

'CR1000

'CR1000 Program for CS505

'Declare Variables and Units

Public FuelM
Public PA_uS

Units FuelM=%
Units PA_uS=uSec

'Define Data Tables

DataTable(Table1,True,-1)
DataInterval(0,60,Min,10)
Sample(1,FuelM,FP2)
Sample(1,PA_uS,FP2)
EndTable

'Main Program

BeginProg
Scan(10,Sec,1,0)

'CS505 Fuel Moisture Sensor measurement FuelM and PA_uS:

If IfTime(0,1,Hr) Then
PortSet(1,1)
PeriodAvg(PA_uS,1,mv2500,1,0,0,10,50,1,0)
FuelM=PA_uS*0.001
FuelM=-220.14+(365.89*FuelM)+(-114.96*FuelM^2)
PortSet(1,0)
EndIf

'Call Data Tables and Store Data

CallTable(Table1)
NextScan
EndProg

CS505 Fuel Moisture Sensor

7

CS505 Fuel Moisture Sensor

6. Maintenance

The sensor element should be changed at least once a year with a new element
in the spring. Since the characteristics of wood change so rapidly, more
frequent replacements may be desirable.

To change the sensor element, loosen the Phillips head screws and replace
with the new element. Tighten the screws after replacing the element.

8

Appendix A. Explanation of Experimental Data

EXPERIMENTAL DATA ERROR DISTRIBUTION

6

Error % WATER

CONTENT
(by weight)

5

4

RMS ERROR 0.98%

3

2

1

0

-1

-2

-3

-4

-5

-6
0 102030405

RMS ERROR 1.43%

RMS ERROR 2.21%

RMS ERROR 2.37%

% WATER CONTENT

(by weight)

0

FIGURE A-1. Experimental Data Error-Distribution

Experiments were conducted to characterize measurement error and to
determine the calibration polynomial coefficients used to convert the output
signal to percent moisture content.

Populated circuit boards (before epoxy) oscillate with a period in the range of

0.6761 and 0.6780 milliseconds. In these experiments, three worst-case units
were chosen. Only fuel moisture sticks that pass the standard rigorous
selection criteria and then additional sorting for both oven-dry density and
sorption qualities are chosen for production. For this experiment, 36 fuel
moisture sticks were randomly selected from 300 production units. Electronic
measurements were compared to actual stick weights. The sticks were soaked
for 45 minutes, then after a five-minute dry, measured electrically and weighed
every 10 to 60 minutes until they reached 15%. Then the sticks were placed in
a 103°C oven for further drying; more measurements were taken. At each
weigh point the sticks where rotated and measured by each of the three
electronic units. Over one thousand data points were measured for this
calibration experiment.

A-1

Appendix A. Explanation of Experimental Data

The full scale range is broken into four sub ranges: 0-10, 10-20, 20-30, and
30-50 percent. The computed rms errors are shown in Table 1. For each range
band an error band was determined in which more than 90 percent of all
measurements fall (also shown in Table A-1 and Figure A-1).

TABLE A-1. Accuracies at Measurement Ranges

Range

0 to 10%
10 to 20%
20 to 30%
30 to 50%

90% of All
Measurements

rms Error

±2% ±1%
±3% ±1.5%
±5% ±2.2%
±6% ±3%

*At least ninety percent of all experimental data fall within
these error bands at the noted range divisions.

The above accuracy is a static accuracy derived at slow changing conditions
with experimental data. In rapidly changing conditions (e.g., in the beginning
of a rain event) the rate of response for each wood dowel differs. After
sufficient time to equilibrate, the dowels will come to the same water content.
This difference in rate of response is inherent in the traditional weighing fuel
stick racks. The effects are lessened by the additional sorting of the dowels
performed at the factory. Readings above 50% are caused by surface water on
the probe or other external factors. Readings are mathematically limited to
70%.

The sensor error is the sum of three influences:

A-2

1. Error due to the variability and non-reproducibility of the response
characteristics of the wood: density, sorption characteristics, resin
content, etc.

2. Error due to the aging of the wood (cracking, discoloration, mass loss as
resin evaporates). This effect is not a factor for new sticks.

3. Offset error due to the electronic circuitry interchang eability, this error is
negligible over 10% fuel moisture.

This is a blank page.

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