FAQs Shock & Vibration Data Loggers

1. What is the difference between measurement ranges?

The Slam Stick products are available in five different measurement ranges: ±16g, ±25g, ±100g, ±500g, or ±2000g. The part number of the product specifies this range (refer to the Slam Stick C datasheet or Slam Stick X datasheet for part numbering information). The Slam Stick C has 13-bit resolution while the Slam Stick X products have 16-bit resolution. This means that there are 2^16 (65,536) acceleration levels that the device can measure. As the measurement range increases, so does the difference between each measurable acceleration level. The noise level also increases as the measurement range increases. All other characteristics of the unit are the same: including cost, form factor, battery life, etc.

Check out our blog post on accelerometer specifications for some more information on what all these specs mean.

2. Why choose the aluminum enclosure?

The Slam Stick X is available with an aluminum enclosure to provide customers with an even more accurate, durable and versatile shock and vibration data recorder. The significantly stiffer aluminum enclosure makes it ideal for shock testing, high frequency vibration testing, and applications where accuracy and durability are paramount and semi-permanent mounting, for instance epoxy or bolting, is available.  The aluminum enclosure is not available for the Slam Stick C.

Frequency Response Plot

3. What is the MEMS/DC accelerometer option and why do I need it?

The MEMS accelerometer (or DC Option) can measure static or near static accelerations such as gravity or very slow vibrations.  Customers interested in orientation will need to be able to measure the gravity vector that the MEMS accelerometer enables.  The MEMS accelerometer will be also be required for applications looking to measure slow vibrations/accelerations such as marine (the sea moves slowly!), wind turbines, etc.

The accelerometer in the Slam Stick C is this MEMS accelerometer.  The main accelerometer in the Slam Stick X is piezoelectric based and has a low frequency roll off; this means that it can't measure static or near static accelerations.  The Slam Stick X does however include an option to have this MEMS accelerometer AND the main triaxial accelerometer (the product would have 8 channels of data: 3 acceleration channels from the main piezoelectric accelerometer, 3 channels from the DC response capacitive MEMS accelerometer, temperature, and pressure).  This is especially helpful to customers who want both high frequency (and amplitude) shock or vibration data along with slower or static acceleration/vibration data.  The MEMS accelerometer is also more power efficient so it can extend the battery life when used for acceleration triggering.  

Please note that the DC accelerometer is "only" 16g, 13-bit, and can sample up to 3,200 Hz.  The below plot shows the frequency response of these two different accelerometers.

Frequency Response Plot

Check out our blog on accelerometer selection that provides a quick overview of different accelerometer types and provides some help on how to select the right one for your application.  The main accelerometer in the Slam Stick X is voltage mode piezoelectric and the main accelerometer in the Slam Stick C is a capacitive MEMS accelerometer.

4. How can I extend the battery life of the Slam Stick vibration data logger?

The Slam Stick vibration recorders have a variety of triggering options which can be used to extend the battery life.  Using a time based trigger will consume the least power.  For example, the Slam Stick C with a 10% duty cycle (record for 1 minute, sleep for 9 minutes) will extend the battery life over 7 times.  Using a temperature, pressure, or MEMS accelerometer trigger will consume about 1/10th the power when compared to regular recording mode.  Note that for the main accelerometer in the Slam Stick X, an acceleration based trigger only extends the battery life by about 20%.  

Both Slam Stick products can also be plugged into power during a recording so that line power, a computer, or an external power supply such as a standard portable phone charger can be used.  The Slam Sticks have a 150 mAh battery for reference.  Beware of some portable chargers that have a "smart" auto shut-off feature once the device is charged.  You'll need a product that doesn't have this feature such as the V15 4,000 battery or V44 12,000 mAh battery from Voltaic.

When plugged into an external power source, the data logger will record until it runs out of storage.

Refer to the Slam Stick C datasheet or Slam Stick X datasheet for more information.

5. Can the Slam Stick stream data in real time?

No, the Slam Stick vibration recorders can not stream data.  See a blog post on different ways to measure vibration for alternative equipment that can perform this functionality.  Midé is aware that this is a highly desired feature and is developing the capability for a future product/variant.

6. Why does the Slam Stick X not measure a 1g acceleration when laying at rest on a flat surface?

The Slam Stick X's main accelerometer can't measure slow vibrations or static accelerations like gravity, see question 3.  The Slam Stick C does have this capability and an X can be purchased with an additional MEMS accelerometer for this functionality also.  Check out our blog on accelerometer selection that provides a quick overview of different accelerometer types and why some can't measure slow or static accelerations like gravity.

7. What happens when the Slam Stick is subjected to accelerations outside its measurement range?

The Slam Stick devices often are used in pretty harsh environments and will see accelerations outside its measurement range.  The MEMS accelerometer has no issue with these accelerations and will just "flat line" at +/- 16g.  The main accelerometer in the Slam Stick X though is a piezoelectric based accelerometer and will experience this "flat line" at its maximum measurement range followed by an exponential decay as shown.

Slam Stick X exceeded measurement range

This happens because the accelerometer's charge amplifier is saturated due to experiencing acceleration outside its measurement range. PCB Piezotronics has a very good technical document detailing why this occurs.  Some customers are hesitant to believe that such a high amplitude acceleration occurred; what often happens though is that a high amplitude and high frequency acceleration occurred.  It can be so high frequency that it will take place between samples even when sampling at 20 kHz.  When such a high frequency impact happens though there is very little energy in the impact so engineers can ignore the data.

When you see this happen you have a few options.  You can get a unit with a higher measurement range.  Or you can try and use some type of mechanical filter such as duct seal putty to filter out this high frequency acceleration.  The structure that the Slam Stick is mounted to should also be looked at to ensure it isn't hitting its own natural frequency during these events.  Some customers use mounting fixtures which aren't stiff enough which can amplify shock/vibration events.  Lastly, you can continue using the unit you have in the same manner (these events won't damage the Slam Stick); and ignore the half second or so of data during these decays.

8. Can the Slam Stick Lab integrate acceleration data to calculate velocity or displacement?

The software can’t currently do any integration, great question though!  The Slam Stick Lab can export data though to both MATLAB or Excel so that the engineer can do some post processing themselves.  Here’s a link to a simple function in MATLAB that can perform an integration of numeric data.  There’s also a few Excel examples out there that do a similar trapezoidal integration.  We are working on adding this functionality into the Lab at some point this year; but there are quite a few other features that are currently higher up on the list.

If you need displacement data, we encourage you to get either the Slam Stick C or the Slam Stick X with DC and perform the integration only on the DC accelerometer channels.  Because the higher frequency/amplitude accelerometer in the Slam Stick X is an AC-response accelerometer, the output of this device will never be able to perfectly track the peak of long duration shock/acceleration events.  At the end of the shock event the output of the AC coupled accelerometer will produce an undershoot (offset).  These seemingly small amplitude deviations can result in significant errors during numeric integration.  The DC response accelerometers do not have this same problem because it can follow the “slow-moving” input accurately.  Check out our blog on accelerometer selection that provides a quick overview of different accelerometer types and provides some more information on integrating acceleration data. 

9. What happened to the original Slam Stick (the Slam Stick Lite)?

The original Slam Stick vibration recorder was developed and released in 2010.  This product was marketed as a vibration environment characterization tool for Midé's energy harvesting customers.  We quickly found that there was a real need in the marketplace for such a device for general vibration/acceleration analysis.  The US Navy saw this device and realizing the potential, funded Midé to advance the technology to what is now the Slam Stick C and X.  See our news story on more background on this development program.

The Slam Stick Lite, although a neat little product, was meant as more of a development tool than a highly accurate analysis tool.  As such it had a number of areas where improvement was needed including battery life, file structure, analysis software (developed into the Slam Stick Lab), mechanical mounting, robustness, and most of all... a higher sample rate and measurement range.  This product has been discontinued and replaced with the Slam Stick C and Slam Stick X.  If you're looking for products that are in the same price range as the original Slam Stick check out our blog that provides information on a range of vibration measurement equipment that is commercially available.

10. What's coming next!?

Midé is actively investing in its data logging product line.  We have two new product groups we hope to release in 2016 and have longer term goals of adding more diagnostic capabilities so that health monitoring information can be wirelessly transmitted to the engineer.

In the short term we will be launching a Slam Stick product with a piezoresistive accelerometer for shock testing.  Then we are working on adding a 9 degree-of-freedom sensor (gyroscope, accelerometer, and magnetometer) to all our products so that users will now have absolute orientation of their data logger during shock and vibration testing.

Following these products, Midé will expand upon the Slam Stick platform to develop a data acquisition system with up to 8 analog input channels and additional embedded sensors.  This product will simplify testing needs of engineers in other applications besides just vibration and shock testing.

In the longer term, Midé plans to add more diagnostic and wireless capability to our products.  Ideally customers could develop their own health monitoring algorithm that Midé's system would run to determine if and when an "event" occurred.  This information would then have to be wirelessly transmitted to the user.

As always, the Slam Stick Lab software will continue to be improved to meet the needs of these new products and other functionality that customers request.  Please contact us with any feature or product requests you may have.  We value and rely on our customers' feedback to continue to advance and improve our products!