Campbell CDM-VW300 Series User manual

USER MANUAL
Issued: 29.10.13
Copyright © 2013 Campbell Scientific Inc.
Printed under licence by Campbell Scientific Ltd.
CSL 995
CDM-VW300 Series
Dynamic Vibrating-Wire
Analyzers

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
This guarantee applies for twelve months from date of delivery. We will repair
or replace products which prove to be defective during the guarantee period
provided they are returned to us prepaid. The guarantee will not apply to:

Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific

Batteries

Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs incurred
in removing and/or reinstalling equipment. This guarantee and the Company’s
obligation thereunder is in lieu of all other guarantees, expressed or implied,
including those of suitability and fitness for a particular purpose. Campbell
Scientific is not liable for consequential damage.
Please inform us before returning equipment and obtain a Repair Reference
Number whether the repair is under guarantee or not. Please state the faults as
clearly as possible, and if the product is out of the guarantee period it should
be accompanied by a purchase order. Quotations for repairs can be given on
request. It is the policy of Campbell Scientific to protect the health of its
employees and provide a safe working environment, in support of this policy a
“Declaration of Hazardous Material and Decontamination” form will be issued
for completion.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package. Complete the “Declaration of
Hazardous Material and Decontamination” form and ensure a completed copy
is returned with your goods. Please note your Repair may not be processed if
you do not include a copy of this form and Campbell Scientific Ltd reserves
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Note that goods sent air freight are subject to Customs clearance fees which
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greater than the cost of the repair.
Campbell Scientific Ltd,
Campbell Park, 80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

PLEASE READ FIRST
About this manual
Please note that this manual was originally produced by Campbell Scientific Inc. primarily for the
North American market. Some spellings, weights and measures may reflect this origin.
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
In addition, while most of the information in the manual is correct for all countries, certain information
is specific to the North American market and so may not be applicable to European users.
Differences include the U.S standard external power supply details where some information (for
example the AC transformer input voltage) will not be applicable for British/European use. Please note,
however, that when a power supply adapter is ordered it will be suitable for use in your country.
Reference to some radio transmitters, digital cell phones and aerials may also not be applicable
according to your locality.
Some brackets, shields and enclosure options, including wiring, are not sold as standard items in the
European market; in some cases alternatives are offered. Details of the alternatives will be covered in
separate manuals.
Part numbers prefixed with a “#” symbol are special order parts for use with non-EU variants or for
special installations. Please quote the full part number with the # when ordering.
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse
but sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, Campbell Park, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone] Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

i
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. Introduction................................................................1
2. Cautionary Statements..............................................2
3. Initial Inspection ........................................................2
4. Overview.....................................................................2
4.1 Channel Allocations.............................................................................3
4.2 Measurement Rates..............................................................................3
4.3 Integrated Thermistor Measurement ....................................................4
4.4 Laboratory Mode..................................................................................4
4.5 Field Mode...........................................................................................5
4.6 Data Uses .............................................................................................5
4.6.1 Static Measurements .....................................................................5
4.6.2 Dynamic Measurements................................................................5
4.6.3 Thermistor Measurements.............................................................6
4.6.4 Rainflow Histograms ....................................................................6
4.6.5 System Diagnostics.......................................................................6
5. Specifications ............................................................6
5.1 Features................................................................................................6
5.2 Specifications.......................................................................................7
6. Installation..................................................................9
6.1 Laboratory-Mode Installation ............................................................10
6.1.1 Laboratory-Mode Installation Equipment...................................10
6.1.2 Laboratory-Mode Installation Procedure ....................................10
6.2 Field-Mode Installation......................................................................16
6.2.1 Field-Mode Installation Equipment ............................................16
6.2.2 Field-Mode Installation Procedure..............................................16
7. System Operation....................................................23
7.1 PC Based Tools..................................................................................23
7.1.1 Software and Driver Installation.................................................23
7.1.2 Using DVWTool.........................................................................24
7.1.2.1 Ensure Connection is Active ............................................24
7.1.2.2 DVWTool Settings Editor................................................25
7.1.2.3 Button and Field Descriptions..........................................25
7.1.3 Using DevConfig ........................................................................26
7.1.3.1 Ensure Connection is Active ............................................26
7.1.3.2 DevConfig Settings Editor ...............................................27
7.2 Using the Datalogger..........................................................................27
7.3 Using the SC-CPI Interface................................................................28
7.4 Using Power Supplies ........................................................................28
7.4.1 CDM-VW300 Series Analyzer Power........................................28
7.4.2 Data-Acquisition System Power .................................................28

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7.5 Configuring the CDM-VW300 Analyzer...........................................29
7.5.1 Device Name...............................................................................31
7.5.2 CPI Bus Speed ............................................................................31
7.5.3 Operating System Version ..........................................................31
7.5.4 Operating System Date ...............................................................32
7.5.5 Analyzer Serial Number .............................................................32
7.5.6 Display Rate................................................................................32
7.5.7 Dynamic Sample Rate.................................................................32
7.5.8 Device Type................................................................................32
7.5.9 CPI Bus Address.........................................................................32
7.5.10 System Options...........................................................................32
7.5.11 Channels Enabled........................................................................32
7.5.12 Desired Resonant Amplitude ......................................................33
7.5.13 Minimum- and Maximum Cut-Off Frequencies.........................33
7.5.14 Frequency-Output Format...........................................................33
7.5.15 Multipliers and Offsets ...............................................................33
7.5.16 Steinhart-Hart Coefficients .........................................................33
7.5.17 Rainflow-Histogram Output Configurations...............................33
7.6 Sensor Selection.................................................................................33
7.6.1 Frequency Considerations...........................................................34
7.6.2 Noise Performance......................................................................34
7.7 System Connections...........................................................................34
7.7.1 CDM-VW300 to PC Connection................................................34
7.7.2 CDM-VW300 to Sensor Connection ..........................................35
7.7.3 CDM-VW300 to SC-CPI Connection.........................................37
7.7.4 CDM-VW300 to Power Connection...........................................39
7.7.5 Earth Ground Connections..........................................................41
7.7.6 Communication Connections......................................................41
7.7.6.1 SC-CPI to CPI Bus Connection........................................41
7.7.6.2 Datalogger to SC-CPI Connection ...................................41
7.7.7 Maximum Number of Analyzers on a Datalogger......................42
7.8 Operating System...............................................................................43
7.9 Power-Up Sequence...........................................................................43
7.10 CRBasic Programming.......................................................................43
7.10.1 Writing Programs........................................................................43
7.10.2 Sending Programs to the Datalogger...........................................45
7.11 System Adjustments...........................................................................45
7.11.1 Frequency Range ........................................................................45
7.12 System Validation..............................................................................46
7.12.1 Sensor Validation........................................................................46
7.12.2 Monitoring System Performance ................................................46
7.12.2.1 Monitoring with DVWTool Software ..............................48
7.12.2.1.1 Fault Detection ......................................................49
8. Troubleshooting ......................................................49
8.1 Connections........................................................................................50
8.2 Power .................................................................................................50
8.3 Isolating Components ........................................................................50
8.4 Filtering Harmonics ...........................................................................50
8.5 Diagnostic Outputs.............................................................................51
8.5.1 Diagnostic Codes (Dynamic)......................................................51
8.5.1.1 Description of Diagnostic Parameters..............................51
8.5.1.2 Calculating Low- and High-Frequency Boundaries.........52
8.5.1.3 Using Diagnostic Parameters ...........................................53
8.5.1.4 Decoding the Diagnostic Code.........................................53
8.5.1.4.1 Excitation Strength................................................53
8.5.1.4.2 Low-Amplitude Warning Flag ..............................53
8.5.1.4.3 High-Amplitude Warning Flag..............................54
8.5.1.4.4 Low-Frequency Warning Flag...............................54

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8.5.1.4.5 High-Frequency Warning Flag..............................54
8.5.1.4.6 Interpreting the Diagnostic Code...........................54
8.5.2 Standard Deviation of Dynamic Output......................................55
8.6 Factory Default Reset.........................................................................55
9. Glossary...................................................................56
10. References and Attributions...................................56
Appendices
A. Measurement Theory............................................. A-1
A.1 Dynamic Vibrating-Wire Measurements ........................................ A-1
A.1.1 Dynamic and Static Frequencies.............................................. A-2
B. SC-CPI Datalogger to CPI Interface...................... B-1
B.1 Introduction......................................................................................B-1
B.2 Quickstart.........................................................................................B-1
B.3 Overview..........................................................................................B-1
B.4 Specifications...................................................................................B-3
C. CDM Devices and CPI Bus.................................... C-1
C.1 CDM Interconnection and Datalogger Connection..........................C-1
C.1.1 Power ........................................................................................C-1
C.1.2 Interconnect Cable ....................................................................C-1
C.1.3 Speed as a Function of Distance ...............................................C-2
C.1.4 CPI Grounding..........................................................................C-3
C.1.6 Addressing ................................................................................C-3
C.2 Distributed Architecture...................................................................C-3
D. Digits Conversion.................................................. D-1
D.1 Example: Frequency to Digits to Displacement.............................. D-1
E. Calculating Measurement Error............................ E-1
E.1 Example Error Calculation: Geokon Strain Gauge ..........................E-1
E.2 Example Error Calculation: DGSI Embedment Strain Gauge .........E-2
E.3 Example Error Calculation: DGSI Spot-Welded Strain Gauge........E-2
E.4 Example Error Calculation: Geokon 4420 Crack Meter ..................E-2
E.5 Example Error Calculation: DGSI Piezometer 52611099................E-3
F. Thermistor Information ..........................................F-1
F.1 Converting Resistance to Temperature ............................................F-1
F.1.1 Resistance Conversion Example –Geokon Sensor...................F-1
F.2 Accuracy and Resolution .................................................................F-1
G. CRBasic Program Library .....................................G-1
G.1 Dynamic Measurements.................................................................. G-1
G.1.1 20 Hz Measurement Example —One CDM-VW300, Two Channels
.............................................................................................. G-1
G.1.2 20 Hz Measurement Example —One CDM-VW305, Eight Channels
.............................................................................................. G-2

iv
G.1.3 20 Hz Measurement Example —Three CDM-VW305s, 24 Channels
...............................................................................................G-3
G.1.4 20 Hz Measurement Example —Six CDM-VW305s, 48
Channels................................................................................G-5
G.1.5 50 Hz Measurement Example —One CDM-VW300, Two Channels
...............................................................................................G-7
G.1.6 50 Hz Measurement Example —One CDM-VW305, Eight Channels
...............................................................................................G-9
G.1.7 50 Hz Measurement Example —Three CDM-VW305s, 24 Channels
.............................................................................................G-10
G.1.8 50 Hz Measurement Example —One CDM-VW300, Two Channels,
Rainflow Histogram ............................................................G-11
G.1.9 50 Hz Measurement Example —One CDM-VW305, Eight Channels,
Rainflow Histogram ............................................................G-12
G.1.10 50 Hz Diagnostic Example —One CDM-VW300, Two
Geokon 4000 Sensors with FieldCal().................................G-14
G.1.11 50 Hz Measurement Example —One CDM-VW300, Two
Geokon 4000 Sensors with FieldCal().................................G-16
G.1.12 50 Hz Measurement Example —One CDM-VW300, Two
Geokon 4000 Sensors with FieldCal() and CardOut() to
CF........................................................................................G-18
G.1.13 50 Hz Measurement Example —One CDM-VW300, Two
Geokon 4000 Sensors with FieldCal() and TableFile() to
CF........................................................................................G-19
G.1.14 100 Hz Measurement Example —One CDM-VW300, Two Channels
.............................................................................................G-21
G.1.15 100 Hz Measurement Example —One CDM-VW305,
Eight Channels ....................................................................G-22
G.2 Static Measurements ......................................................................G-23
G.2.1 1 Hz Measurement Example —One CDM-VW300, Two
Channels..............................................................................G-23
G.2.2 1 Hz Measurement Example —One CDM-VW305, Eight Channels
.............................................................................................G-24
Figures
4-1. Two-channel CDM-VW300 wiring panel............................................3
4-2. Eight-channel CDM-VW305 wiring panel ..........................................3
4-3. Measurement speeds of the AVW200 and CDM-VW300 analyzers...4
4-4. Single-coil vibrating-wire sensor including coil and thermistor
outputs..............................................................................................4
4-5. Laboratory-mode measurement system diagram..................................5
4-6. Field-mode data-acquisition system diagram.......................................5
6-1. Laboratory-mode measurement system..............................................10
6-2. 12 Vdc power connection on the CDM-VW300................................11
6-3. USB receptacle on CDM-VW300 and Type-Micro-B connector
of USB cable ..................................................................................11
6-4. Sensor connection on a CDM-VW305...............................................14
6-5. Three-wire vibrating-wire sensor connections...................................15
6-6. Five-wire vibrating-wire sensor connections .....................................15
6-7. Field data-acquisition system.............................................................17
6-8. CPI communications links .................................................................19
6-9. Datalogger to SC-CPI connection......................................................19
6-10. Connecting the CPI ports of the SC-CPI and CDM-VW300.............20
6-11. Install CPI bus terminator ..................................................................20
6-12. Power connection...............................................................................21
6-13. Earth ground connections...................................................................21
7-1. DVWTool Settings Editor and Data Display .....................................25
7-2. DevConfig Settings Editor.................................................................27
7-3. 12 Vdc power transformer for laboratory-mode installation..............28

v
7-4. USB port on the CDM-VW300..........................................................35
7-5. Three-wire vibrating-wire sensor leads..............................................35
7-6. Three-wire vibrating-wire sensor connection.....................................36
7-7. Five-wire, vibrating-wire sensors leads..............................................36
7-8. Five-wire vibrating-wire sensor connection.......................................37
7-9. SC-CPI and CDM-VW300 CPI ports with RJ45 cable marked
with yellow tape..............................................................................38
7-10. CPI terminator installed .....................................................................38
7-11. Multiple analyzers on a CPI bus ........................................................39
7-12. Installing 12 Vdc transformer on the CDM-VW300..........................40
7-13. Daisy-chaining 12 Vdc power input on the CDM-VW300................40
7-14. Earth ground connections...................................................................41
7-15. CR3000 and SC-CPI connections ......................................................42
7-16. LoggerNet connect screens showing frequencies from
CDM-VW300.................................................................................47
7-17. RTDAQ screens showing frequencies in Public table.......................48
7-18. Dynamic Vibrating-Wire Tool Box Fault Indicators .........................49
A-1. Timing of dynamic vibrating-wire measurements .......................... A-2
B-1. Connection to the SC-CPI in DevConfig .........................................B-2
C-1. CPI pin assignments.........................................................................C-2
C-2. Long cable lengths of a distributed CPI bus.....................................C-4
D-1. Geokon Calibration Report of a Sensor without a Thermistor........ D-2
F-1. Temperature measurement error at three temperatures as a
function of lead length. Wire is 22 AWG with 16 ohms per
1000 feet.......................................................................................F-2
F-2. Temperature measurement error on a 1000 foot lead. Wire is
22 AWG with 16 ohms per 1000 feet...........................................F-3
F-3. Temperature measurement error on a 3000 foot lead. Wire is
22 AWG with 16 ohms per 1000 feet...........................................F-3
F-4. Temperature measurement error on a 5000 foot Lead. Wire is
22 AWG with 16 ohms per 1000 feet...........................................F-4
Tables
5-1. CDM-VW300 / Datalogger Compatibility...........................................7
5-2. CDM-VW300/305 Sensor Resonant Frequency Range (Hz)...............8
5-3. CDM-VW300/305 Effective Frequency Measurement Resolution4....8
6-1. CDM-VW300 Status LED States.......................................................15
6-2. DVWTool and CRBasic Settings.......................................................17
7-1. Summary of CDM-VW300 Configuration Settings...........................30
7-2. Relationship of Sample Rate and Sensor Frequency..........................34
7-3. Number of Analyzers and Channels Supported by a Datalogger
Writing to CF Card.........................................................................42
7-4. CDM-VW300 Scan Rate / Datalogger Scan() Interval Pairings ........44
7-5. CDM-VW300 Channel-Status LED States ........................................46
8-1. Scan Rate and Boundary Resolution..................................................53
8-2. Diagnostic Code Ranges ....................................................................55
C-1. Maximum Potential Speed as a Function of Distance1.....................C-2

1
CDM-VW300 Series Dynamic Vibrating-
Wire Analyzers
Configuring a dynamic vibrating-wire measurement system requires an integrated
system-wide approach. Please review this manual before connecting hardware
together or to the PC. The ResourceDVD, which ships free of charge with most
Campbell Scientific instrumentation orders, contains the following tools that will
help you configure a dynamic vibrating-wire analyzer system:
A copy of this manual
DVWTool Dynamic Vibrating-Wire Toolbox software for CDM-VW300
support
DevConfig Device Configuration Utility software
Required datalogger operating systems
Other support information and downloads are available at
www.campbellsci.com/cdm-vw300-support.
1. Introduction
Vibrating-wire sensors are commonly used in geotechnical or structural
monitoring applications to measure strain, load, tilt, inclination, temperature,
pressure, extension, and crack movement. CDM-VW300 Series Dynamic
Vibrating-Wire Analyzers facilitate sub-second measurement of vibrating-wire
sensors. These analyzers perform advanced excitation, spectral analysis, and
digital signal processing to obtain high-accuracy measurements. Data are stored
on a Campbell Scientific datalogger, which is normally used to control the system
in field installations.
The CDM-VW300 has two modes of operation:
Laboratory mode
oManual operation
oDoes not require a datalogger
oRequires a PC
oUsed in short-term evaluation
oReal-time data and metadata are monitored with PC
Field mode
oAutomated operation
oRequires a datalogger
oPC used only for setup and collection of data from datalogger
oUsed in long-term monitoring applications
oTime-series data and metadata stored in datalogger memory
Two analyzer models are available in the CDM-VW300 series:
CDM-VW300 (two channels)
CDM-VW305 (eight channels)
See Table 5-1, CDM / Datalogger Compatibility, in Section 5, Specifications, for
datalogger compatibility information.
Other than a few clearly noted exceptions, any discussion in this manual of the
CDM-VW300 also applies to the CDM-VW305.

CDM-VW300 Series Dynamic Vibrating-Wire Analyzers
2
Before using the CDM-VW300, please study
Section 2, Cautionary Statements
Section 3, Initial Inspection
Detailed installation, operation, and troubleshooting information can be found in
the remaining sections.
2. Cautionary Statements
CAUTION —Do not connect power to the system until it is completely
assembled.
IMPORTANT —Do not connect the CDM-VW300 analyzer or SC-CPI
interface to a PC until AFTER installing DVWTool or DevConfig on the PC.
Consult Section 7.1.1, Software and Driver Installation, for more
information.
All references to DVWTool mean Dynamic Vibrating-Wire Tool Box software
version 1.0 or later. DVWTool is available on current versions of the
ResourceDVD that ships with CDM-VW300 series analyzers. All references
to DevConfig mean Device Configuration Utility software version 2.04 or
later. DevConfig is available from the these three sources:
oResourceDVD shipped with CDM-VW300 series analyzers
owww.campbellsci.com/downloads (no charge)
oInstallations of LoggerNet, PC400, PC200W, or RTDAQ
software. Check the Help | About screen in DevConfig for the
version number.
3. Initial Inspection
CDM-VW300 series analyzers ship with,
o1 each pn #29389 CDM Parts Kit
o1 each ResourceDVD, which contains DVWTool and current DevConfig
software.
Upon receipt of the CDM-VW300, inspect the packaging and contents for
damage. File damage claims with the shipping company.
Thoroughly check all packaging material for product that may be concealed
inside it. Check model and part numbers, and product descriptions against the
shipping documents. Model or part numbers are found on each product.
Cable numbers are normally found at the end of the cable that connects to the
measurement device. Check that expected cable lengths were received.
Contact Campbell Scientific immediately concerning any discrepancies.
4. Overview
Single-coil vibrating-wire sensors are preferred in many applications because they
are stabile, accurate, and durable. CDM-VW300 Series Dynamic Vibrating-Wire
Analyzers make accurate high-speed measurements of the resonant frequencies of
these sensors at sub-second intervals using advanced excitation and signal
processing techniques, including spectral analysis. Resonant frequency data are
passed with diagnostics to a Campbell Scientific datalogger. Applications include
characterization of events that require rapid measurements and data storage, and

User Manual
3
measurement of sensor signals too weak to be measured with other
instrumentation. See Appendix A, Measurement Theory, for more information.
Dynamic vibrating-wire measurements require a complete system of
instrumentation. This manual focuses on the use of CDM-VW300 series
analyzers, but it also gives basic guidance on system configuration.
4.1 Channel Allocations
As illustrated in Figure 4-1, the CDM-VW300 simultaneously measures two
vibrating-wire sensors. Figure 4-2 shows that the CDM-VW305 has the capacity
to measure eight sensors. When more than eight channels are needed, multiple
devices are attached to the same datalogger through the CPI bus. See Section
7.7.7, Maximum Number of Analyzers on a Datalogger, and Appendix C, CDM
Devices and CPI Bus, for details on connecting multiple analyzers to a CPI bus.
Figure 4-1. Two-channel CDM-VW300 wiring panel
Figure 4-2. Eight-channel CDM-VW305 wiring panel
4.2 Measurement Rates
CDM-VW300 analyzers use patented techniques to measure sensors at rates from
1 to 333.3 Hz. Systems that exclusively require rates slower than 1 Hz should use
a Campbell Scientific AVW200-Series Vibrating-Wire Spectrum Analyzer.

CDM-VW300 Series Dynamic Vibrating-Wire Analyzers
4
Figure 4-3. Measurement speeds of the AVW200 and CDM-VW300
analyzers
4.3 Integrated Thermistor Measurement
Many vibrating-wire sensors include an integrated thermistor to allow for
temperature compensation of the vibrating-wire measurement. The CDM-VW300
supports thermistor measurements and the associated temperature compensation
required in some applications.
Figure 4-4. Single-coil vibrating-wire sensor including coil and thermistor
outputs
4.4 Laboratory Mode
Laboratory mode allows for examination and validation of specific measurements
types without a datalogger, such as might occur before field deployment. As
shown in Figure 4-5, a connection is made from the CDM-VW300 to a personal
computer using a USB cable. Campbell Scientific DVWTool software on the PC
enables observation of sensor outputs and configuration of the CDM-VW300 to
measure sensors. Specific procedures can be found in Section 6.1.2, Laboratory-
Mode Installation Procedure.
Vibrating Wire
Thermistor
Stainless Steel Housing
4-Conductor Cable
Filter
Plucking and Pickup Coils
Diaphragm
Internal Bulkhead Seal
Two Coil Outputs
Two Thermistor
Outputs

User Manual
5
Figure 4-5. Laboratory-mode measurement system diagram
4.5 Field Mode
Field mode is used for long-term measurement and data acquisition. As shown in
Figure 4-6, a connection is made from the CDM-VW300 to a Campbell Scientific
datalogger through the SC-CPI interface. A Campbell Scientific datalogger with a
customized CRBasic program configures, controls, and collects data from the
CDM-VW300. Specific installation procedures are found in Section 6.2.2, Field-
Mode Installation Procedure.
Figure 4-6. Field-mode data-acquisition system diagram
4.6 Data Uses
Users should consult authoritative sources concerning the use of vibrating-wire
data in structural analysis applications. Following is a short introduction to the
use of data made available by CDM-VW300 series analyzers.
4.6.1 Static Measurements
Each sensor is measured for a static frequency once per second. The static
frequency is used to obtain a result with finer spectral bin resolution than that
which can be achieved at the dynamic measurement rates. This measurement can
be helpful in detecting the rare case, for example, in which a noise frequency very
near the resonant frequency affects dynamic sampling measurements.
4.6.2 Dynamic Measurements
Each analyzer can be configured in a 20, 50, 100, 200, or 333.3 Hz sampling
mode. By capturing multiple readings each second from a vibrating-wire sensor,
rapid changes or events can be captured and evaluated. Due to the Nyquist
sampling theorem, only responses equal to or less than half of the sampling

CDM-VW300 Series Dynamic Vibrating-Wire Analyzers
6
frequency can be detected and characterized. Event-based data capture techniques
programmed into the controlling datalogger can be helpful to ensure useful data
are captured under the right event conditions. In this way, storage and retrieval of
less-useful data are avoided.
4.6.3 Thermistor Measurements
Each vibrating-wire sensor input channel has inputs for the thermistor that is
usually built into a vibrating-wire sensor. The temperature measurement is
normally used to correct the frequency measurement for temperature changes. A
24-bit measurement circuit ensures high-accuracy resistance measurements, which
are converted to temperature. Guidance about the impact of temperature on the
vibrating wire is usually provided by the manufacturer in documentation provided
with each individual sensor. Contact the sensor manufacturer if more information
is required.
4.6.4 Rainflow Histograms
Rainflow histograms are 3-D representations of the rainflow counting algorithm of
Matsuiski and Endo (1968). Rainflow histograms can be used to monitor fatigue
levels of structures under stress, such as components of a large-scale
transportation bridge. The histograms are calculated by the CDM-VW300
analyzer to ease the processing burden required of the controlling datalogger.
CRBasic Help topic for the Rainflow() instruction has more information about
rainflow histograms.
4.6.5 System Diagnostics
Several diagnostic values will help you scrutinize basic CDM-VW300
measurements. Excitation level and low / high frequency or amplitude warnings
are provided for each dynamic measurement. A standard deviation is provided
once each second.
Excitation level is bounded by setting the amplitude at which the wire in the
sensor is to be maintained. That figure is reported so that excitation levels can be
monitored. If the analyzer-sensor system experiences a low amplitude, high
amplitude, low-frequency, or high frequency condition, that information is also
provided.
Once each second, a standard deviation of a dynamic measurement is provided.
Unexplained changes in the standard deviation from baseline levels may indicate
noise or other interference.
5. Specifications
5.1 Features
Measurement of standard, single-coil circuit, vibrating-wire sensors
Dynamic-sampling rates of 20 to 333.3 Hz
On-board frequency-output conversion
Two (CDM-VW300) or eight (CDM-VW305), simultaneously-sampled
channels per module
Time synchronization of multiple modules using one datalogger
Thermistor input for each vibrating-wire channel measured at 1 Hz

User Manual
7
On-board temperature conversion
Rainflow-histogram compilation
Superior noise immunity and effective measurement resolution (precision)
Continuous resonant vibration in the sensor
Spectral analysis method protected under U.S. patent no. 7,779,690. An
additional U.S. patent that relates to the dynamic vibrating-wire measurement
technique is pending.
5.2 Specifications
Electrical specifications are valid from –25 to 50 °C unless otherwise specified.
Non-condensing environment required. Specifications are subject to change.
Compatibility:
Table 5-1. CDM-VW300 / Datalogger Compatibility
Datalogger
Connect with
SC-CPI1
Module
Maximum
Measurement
Rate (Hz)
Maximum CDM-
VW305 Analyzers
at Max Rate /
Maximum
Channels
CR3000
*
1002
1/8
–
–
50
3/24
–
–
20
6/48
CR800 /
CR1000
*
50
1/8
–
–
20
4/32
Frequency measurement:
A vibrating-wire circuit is excited and
measured through the same coil
connection. Sinusoidal excitation
persists for a few cycles of the wire
oscillation. The wire is maintained in a
continuously vibrating state. Excitation
voltage varies automatically to maintain
the desired return signal strength.
Dynamic measurement
rates:
20, 50, 100, 2003, and 333.33Hz
Accuracy:
±(0.005% of reading + effective
measurement resolution)
Input resistance:
5 kΩ
Excitation voltage
Range:
0 to ±3 V (6 V peak-to-peak)
Resolution:
26 mV

CDM-VW300 Series Dynamic Vibrating-Wire Analyzers
8
Sensor resonant frequency
range:
Table 5-2. CDM-VW300/305
Sensor Resonant Frequency Range (Hz)
Sample Rate
Minimum Sensor
Frequency
Maximum Sensor
Frequency
20
290
6000
50
290
6000
100
580
6000
2003
1150
6000
333.33
2300
6000
Effective resolution (precision):
Table 5-3. CDM-VW300/305
Effective Frequency Measurement Resolution4
Sample Rate (Hz)
Noise Level (Hz RMS)5
1
0.005
20
0.008
50
0.015
100
0.035
2003
0.11
333.33
0.45
Sustained input voltage without
damage:
–0.5 to 7.1 V
Temperature measurement:
Temperature measurement is
available for sensors so equipped.
Excitation and half-bridge
measurement circuits are integrated
into the CDM-VW300 and CDM-
VW305 analyzers.
Accuracy:
0.15% of reading6
Resolution:
0.002 Ω RMS @ 5 kΩ thermistor
resistance
Bridge resistor:
4.99 kΩ 0.1%
Excitation voltage:
1.5 V
Measurement rate:
1 Hz