CDM-VW300 2-Channel Dynamic Vibrating-Wire Analyzer
Vibrating-Wire Measurements

Uses patented VSPECT™ technology for noise immunity and industry-leading quality
weather applications water applications energy applications gas flux & turbulence applications infrastructure applications soil applications

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The CDM-VW300 is a two-channel interface that you can use between standard single-coil circuit vibrating-wire sensors and dataloggers to allow shorter intervals between measurements. With the CDM-VW300 interface, you can achieve much faster and better measurements without having to purchase new sensors. Sensors typically used with the CDM-VW300 are strain gages, load cells, pressure transducers, crackmeters, and tiltmeters. 

This interface uses an excitation mechanism that maintains the vibrating-wire sensor in a continuously vibrating state. The interface measures the resonant frequency of the wire between excitations using the patented vibrating-wire spectral-analysis technolgy (VSPECT™). VSPECT provides very fine measurement resolution and also limits the influence of external noise by discriminating between signal and noise based on frequency content. Because of this technology, the signal can be carried through longer cables, giving you flexibility in your sensor and datalogger siting.

You can connect multiple CDM-VW300 modules to one datalogger. The CDM-VW305 is similar to this item, but it has eight channels.

The dynamic vibrating-wire measurement technique is protected under U.S. Patent No. 8,671,758, and the vibrating-wire spectral-analysis technology (VSPECT™) is protected under U.S. Patent No. 7,779,690.

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Benefits and Features

  • Interfaces to standard single-coil vibrating-wire sensors
  • Two simultaneously sampled channels per module; synchronizable across multiple modules
  • Dynamic measurement rates of 20 to 333 Hz
  • Static measurement at 1 Hz made simultaneously with the dynamic measurement
  • Spectral interpolation approach provides superior noise immunity and measurement resolution compared to time-domain period-averaging approach
  • Excitation method provides frequent low-energy pulses to maintain a continuous resonant vibration in the sensor
  • Thermistor input for each vibrating-wire channel is sampled at 1 Hz
  • Datalogger communications via CPI
  • User-configurable, onboard post-processing of the data including frequency output conversion, temperature conversion, and rainflow histogram collection


Detailed Description

In addition to the dynamic vibrating-wire measurement, the CDM-VW300 makes several auxiliary measurements. A static vibrating-wire measurement is made once each second, along with the dynamic measurements, which provides finer measurement resolution and greater immunity to external noise sources. The CDM-VW300 includes a thermistor input channel paired with each vibrating-wire channel, featuring high-precision 24-bit measurements at a 1 Hz rate. Lastly, a rich set of diagnostic parameters is provided with the vibrating-wire data.

The CDM-VW300 has the capability to simplify post-processing of data by computing common values internally. Vibrating-wire data can be reported as measured frequency or as the frequency squared with a multiplier and offset applied. The thermistor data is reported as resistance or is converted to degrees Celsius using the thermistor’s Steinhart-Hart coefficients. The CDM-VW300 also can internally compile rainflow histograms from the final data and report the values at user-specified intervals.

Vibrating-Wire Inputs

Each channel has two terminals for connecting to the coil of the vibrating-wire sensor. Both vibrating-wire terminals are labeled VW and the polarity of the wiring is arbitrary. The sensor is excited and measured through the same connections. Sinusoidal excitation is applied 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.

Thermistor Inputs

Each channel has two terminals for connecting to the thermistor. Both thermistor terminals are labeled T and the polarity of the wiring is arbitrary. The measurement is a half-bridge configuration with the excitation circuitry and completion resistor integrated into the module.


-NOTE- Electrical specifications are valid over a -25° to +50°C range unless otherwise specified. Non-condensing environment required.
Scan Rates 20, 50, 100 Hz
CPI Baud Rate Selectable from 25 kbps to 1 Mbps
Input Resistance 5 kΩ
Excitation Voltage Range 0 to ±3 V (6 V peak-to-peak)
Excitation Voltage Resolution 26 mV
Operating Temperature Range
  • -25° to +50°C (standard)
  • -55° to +85°C (extended)
Measurement Frequency Accuracy ±(0.005% of reading + measurement resolution)
Sustained Input Voltage without Damage -0.5 to +7.1 V
CPI Used for connection to the datalogger. Baud rate selectable from 50 kbps to 1 Mbps. (Allowable cable length varies depending on baud rate, number of nodes, cable quality, and noise environment, but can be as long 2,500 ft under proper conditions.)
USB USB 2.0 full speed connection is available for attaching the device to a PC. (This port is provided to configure the module, send updates, and communicate with the Dynamic Vibrating-Wire Toolbox software. The USB port is not provided for use within a permanent data collection system.)
Mounting Standard 1-in. grid (DIN rail mounting available)
Warranty One year against defects in materials and workmanship
Dimensions 20.3 x 12.7 x 5.1 cm (8 x 5 x 2 in.)

Measurement Resolution at Sample Rates

-NOTE- Typical values for a 2.5 kHz resonant sensor
1 Hz Sample Rate 0.005 Hz RMS (noise level)
20 Hz Sample Rate 0.008 Hz RMS (noise level)
50 Hz Sample Rate 0.015 Hz RMS (noise level)
100 Hz Sample Rate 0.035 Hz RMS (noise level)

Sensor Resonant Frequency Range

20 Hz Sample Rate
  • 290 Hz (minimum sensor frequency)
  • 6000 Hz (maximum sensor frequency)
50 Hz Sample Rate
  • 290 Hz (minimum sensor frequency)
  • 6000 Hz (maximum sensor frequency)
100 Hz Sample Rate
  • 580 Hz (minimum sensor frequency)
  • 6000 Hz (maximum sensor frequency)


Completion Resistor 4.99 kΩ 0.1%
Excitation Voltage 1.5 V
Resolution 0.002 Ω RMS (@ 5 kΩ thermistor resistance)
Accuracy 0.15% of reading (Thermistor accuracy and resistance of the wire should be considered as additional errors.)
Measurement Rate 1 Hz

Power Requirements

Voltage 9.6 to 32 Vdc
Typical Current Drain 115 mA (@ 12 Vdc)


Datalogger Considerations

The SC-CPI Datalogger Serial-to-CPI Interface is required to connect the CDM-VW300 to a compatible datalogger (except the CR6). A 5-conductor cable connects the datalogger to the SC-CPI, and an Ethernet cable connects the SC-CPI to the CDM-VW300.

Compatible Contemporary Dataloggers

The datalogger operating system must be version OS 26 or newer.

CR200X Series CR800/CR850 CR1000 CR3000 CR9000X CR6

Compatible Retired Dataloggers

None of our retired dataloggers are compatible.


The CDM-VW300 is not designed to work with multiplexers.



CDM-VW300/305 OS v.04 (563 KB) 10-25-2017

Execution of this download installs the CDM-VW300/305 Operating System on your computer for upload to the CDM-VW300/305 device with Device Configuration Utility.

Note: The CDM-VW300/305 OS V.02 or greater is required to use the CDM-VW300/305 with the CR6 datalogger or with a CR3000/1000/800 datalogger that is using OS 28 or higher. The SC-CPI Operating System will also need to be upgraded to SC-CPI OS V.02. If using a CR3000/1000/800 datalogger with an older OS, an operating system upgrade to the datalogger will be required.

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CDM-VW300 Example Programs (45.4 KB) 05-23-2013

CRBasic program examples for use with the CDM-VW300 and CDM-VW305.

CPI Calculator v.1.0 (2.49 MB) 07-06-2016

The CPI Calculator is a downloadable Microsoft Excel spreadsheet used to estimate the usage and capacity of a CPI network.  The calculator provides an overview on CPI devices including the CDM-A108, CDM-A116, CDM-VW300, CDM-VW305, and the CSAT3B.  The calculator can also estimate the measurement speed of the CDM-A108 and CDM-A116 based on the number of channels and measurement parameters.


The CPI Calculator is an estimation tool and will help you better understand and design CPI networks by considering the following:

  1. What is the capability of each CDM or CPI device
  2. What is the CPI network capacity
  3. How much of the CPI capacity are the CDMs or CPI devices using


DVW Tool Box v.1.2 (13.0 MB) 10-10-2016

DVW Tool Box is an application-specific software tool for demonstration and evaluation of the CDM-VW300 and CDM-VW305 dynamic vibrating-wire interfaces.

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Device Configuration Utility v.2.17 (46.4 MB) 02-13-2018

A software utility used to download operating systems and set up Campbell Scientific hardware. Also will update PakBus Graph and the Network Planner if they have been installed previously by another Campbell Scientific software package.

Supported Operating Systems:

Windows 10, 8.1, 8, and 7 (Both 32 and 64 bit)

View Update History

Frequently Asked Questions

Number of FAQs related to CDM-VW300: 8

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  1. The CDM-VW300 offers two channels for simultaneous reading of two vibrating-wire sensors, whereas the CDM-VW305 offers eight channels for simultaneous measurements. Other than the number of channels supported, both models operate identically.
  2. These devices work with vibrating-wire strain gages, load cells, pressure transducers, crackmeters, and tiltmeters. Any standard, single-coil circuit vibrating-wire sensor should work with these devices.

  3. The frequency outputs generated by the CDM-VW300 or CDM-VW305 can be scaled with known sensor response functions, which are provided by the manufacturer of the sensor. These frequency conversions are used to obtain measurement outputs expressed in the desired engineering units.

  4. Yes. When more than eight channels are needed in a system, multiple CDM-VW300-series devices can be connected to the same datalogger.

    • Each CDM-VW300 device provides two terminals. 
    • Each CDM-VW305 device provides eight terminals.

    Any combination of CDM-VW300 and CDM-VW305 devices can be used to achieve the desired number of total terminals.

    The list below, ordered by datalogger and measurement rate, indicates the maximum number of supported terminals:

    • CR3000, 100 Hz: 8 terminals
    • CR3000, 50 Hz: 24 terminals
    • CR3000, 20 Hz: 48 terminals
    • CR1000, 100 Hz: not supported
    • CR1000, 50 Hz: 8 terminals
    • CR1000, 20 Hz: 32 terminals
    • CR800-series, 100 Hz: not supported
    • CR800-series, 50 Hz: 8 terminals
    • CR800-series, 20 Hz: 32 terminals
  5. To communicate with CDM devices using the CPI protocol, the CR3000, CR1000, CR850, and CR800 dataloggers require an SC-CPI device. Only one SC-CPI device per datalogger is required. It is expected that the design of future Campbell Scientific datalogger products will work with CPI-based modules directly.

  6. The communications protocol used by CDM devices is the CAN Peripheral Interface (CPI), which includes methods that are proprietary to Campbell Scientific.
  7. Yes. Specific types of sensor measurements can be examined and evaluated before the system is deployed to a field site. A datalogger is not used for this type of evaluation. Connect the CDM-VW300-series device directly to a computer using a USB cable. Using DVWTool software (specialized software included with the CDM-VW300 or CDM-VW305), the outputs of the attached vibrating-wire sensors can be observed, and the CDM device can be configured appropriately.
  8. CDM-VW300-series devices can measure vibrating-wire sensors at the following rates: 1 Hz, 20Hz, 50Hz, 100Hz, 200Hz, and 333.3 Hz. CDM-VW300-series devices are designed for measurement periods of 1 s or less.

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