USB Accelerometer White Paper
By Robert Kirker

Predictive Maintenance

Vibration data collection in the Predictive Maintenance market currently uses data collectors designed specifically to only collect and analyze vibration data. Industry trends are moving more and more to Operator Based Maintenance. With the advent of low cost rugged handheld computers operators can now perform and record many maintenance operations at the touch of a screen. When the Techkor Instruments USB accelerometer is properly integrated with a handheld computer, operators can easily collect and store vibration data.
 

M9E-USB Sensor with Intermec 700 Handheld PC

Currently there are a number of handheld vibration sensors available on the market however; these sensors only provide basic overall vibration levels. If an operator detects a problem a vibration expert still needs to be called in. These experts bring their expensive data collectors, obtain the data and then take the data back to their computers, download the data into their database and perform their analysis. In many cases there is limited historical data available to the expert which tends to hinder the analysis of the problem.

Using the Techkor USB accelerometer with a standard handheld computer the operator would be shown the overall vibration level which provides a first level of awareness to the operator but behind the scenes a complete digitized time waveform has been acquired and stored. When the operator docks his handheld computer any data that has been collected is automatically uploaded into the vibration database. If a problem is discovered, by the operator or preset alarms, the vibration expert only needs to access the database and the time waveshapes required to perform a detailed analysis are immediately available for current and past conditions.

The USB accelerometer is an intelligent sensor which stores all the appropriate calibration factors which enables the product to achieve better than ± 3% accuracy. This accuracy is transportable to another handheld computer without having to deal with any additional calibration issues. Along with vibration data the sensor contains a temperature output which can be helpful in monitoring the status of a motor or bearing. By using a computer with multiple USB ports with Host capability additional sensors can be added by just plug and playing. Adding an additional sensor provides the system the capability to perform spin balancing.

For many applications the Techkor USB accelerometer can replace a $10,000 to $20,000 data collection system with a simpler system utilizing an industry standard architecture for less then $5,000 (including the handheld computer).

Test and Measurement

In a typical Test and Measurement situation the following equipment would need to be hooked up, powered up and tested.

• Accelerometer

• Signal Conditioner

• Data acquisition card or box

• Computer

Typical test and measurement setup including accelerometer, signal conditioner, data acquisition device, computer and cables

After all these components have been properly connected together, the system would still need to be properly calibrated. Accelerometer calibration information (mV/g) needs to be manually programmed into the measurement system. In many cases to insure accuracy the entire system then needs to be calibrated from end-to-end. If more than one accelerometer is needed this entire process needs to be repeated for each accelerometer.

The Techkor USB accelerometer significantly reduces testing setup time and calibration. All the components shown in the picture above (except the computer) have been incorporated into the USB accelerometer; the sensor, the signal conditioner, digitizing and all the signal processing. Sensor power is supplied via the USB protocol. Because of this integration one only needs to plug the sensor into a USB port with Host capability and vibration testing can begin.
 

Test and measurement setup using the USB accelerometer only requires the sensor, one cable and a computer

With the USB sensor field calibration is no longer required. Since all the components that need to be calibrated are contained with the sensor an end-to-end calibration comes as part of the sensors manufacturing process. The output of the sensor is a digitized time waveform which can be processed just like any other digitized data. One significant feature of the USB sensor is the ability to improve the current, ± 3% accuracy. If a higher level of accuracy is required the sensor can be tested against a higher accuracy standard and the sensor calibration data can be updated (via the USB interface) to provide this higher accuracy.

Expanding the number of sensors is as simple as plugging more sensors into any available USB port. Routers and other devices can be used to increase the number of USB ports available within a system.
 

Test and measurement setup with multiple USB accelerometers

Using the USB sensor with a LabView driver can reduce setup times from hours to minutes. With the sensor’s end-to-end calibration already in place there is one less chance for variation and error to enter into the measurements.

Custom Applications

With a digital interface, like USB, there are many options that can be incorporated into the sensor depending on a particular application. For higher quantity applications the product can be optimized to meet specific price and performance objectives. In the current USB design a piezoelectric crystal is used in order to acquire the high frequency vibration signals. A MEMS sensor could be incorporated that would provide an overall vibration level at a lower cost. Sensor packaging has a significant impact on price and can be optimized for price and performance for specific applications. With the digital overlay other types of sensors can also be incorporated into a sensor such as temperature, humidity, load, torque and strain sensors.

Conclusion

Techkor Instruments' new USB digital accelerometer significantly reduces the complexity and cost of obtaining accurate and detailed vibration data in several different markets. This approach increases the cost of the sensor but by eliminating the need for an expensive data collector the overall system costs are significantly reduced.

USB Accelerometer White Paper in PDF