- Lithium Batteries
- How Long Can Your Accel Cables Be?
IST Hardware tech tip
Daniel R. Burk
IST Applications Engineering
Hello from IST Applications Engineering!
Times have been busy these past few months in the engineering department: We are finishing up a special project for one of our customers. Once and a while a customer will require a specialized system. IST has traditionally been willing to make minor modifications to our standard product line in order to accommodate test requirements. However, the decision to pursue an engineering modification is made on a case-by-case basis, and is dependent on availability of engineering resources, potential purchase quantity, and lead time. Some unusual projects that we have completed in the past few years included a watertight EDR3C for measurement of undersea vibration of a pipe line, a variable-gain Snapshock Plus for measuring traffic loading of a bridge, and a customized Snapshock Plus for downhole measurement of impacts in an oil drilling application. We've made modified EDR3C recorders for ride characterization of roller coasters, as well. Now that we are close to finishing this special project, we hope to return to development of the next revision of DynaMax Suite, as well as development of some new recording technology.
What's up with Lithium, these days?
Five years ago it seemed that Lithium was the wonderchild of battery technology: Lots of power availability in a small package. Then, regulations concerning the shipment of lithium cells began to make it hard to ship lithium cells. Suddenly, it seemed as if anything that had a hint of Lithium in it was instantly classified as hazardous materials. We've even had some customers report instances where their shippers disassembled the EDR recorder in a zealous hunt for lithium. So, what is the official word in the use & transport of lithium cells? For that answer, I called our primary supplier of lithium cells, Ultralife. Their UV9L battery, which is a 9-volt 1200 maH battery contains 1.45 grams of lithium in a solid cathode design. We recommend the Ultralife battery for use in the Snapshock Plus, as well as 9-volt versions of the EDR3C & EDR3D recorder. Ultralife faxxed the MSDS sheets on that cell, which we have placed in a .pdf for you. UltralifeMSDS They also stated that transport of their lithium power cells is governed by US DOT 49 CFR 173.185(i). which shows that Ultralife batteries can be shipped as non-hazardous material.
The other lithium cell that you will encounter in IST designs is the backup battery. This battery is manufactured by Eagle-Picher, under the "Keeper II" label. This MSDS sheet is available as a .pdf document Eagle-Picher MSDS and IATA excerpt. Tim Godfrey, of Eagle-Picher has stated that the Keeper-II that we use (750 maH capacity) contains less than a half-gram of lithium, and is thus able to be shipped without restrictions. Tim also provided an excerpt out of the IATA spec book which discusses the transport of lithium batteries. Paragraph A45, item 1 covers the exemption under which the Eagle Picher battery falls. Paragraph A45, item 2 covers the exemption for the Ultralife battery. Thus, all lithium batteries used in regular-production IST products can be shipped with no restrictions.
Technical note: How long can you make your accelerometer cables?
The EDR3 and EDR3C/D-series, MSR-series, and EDR4-series all have the capability of using special voltage-mode piezoelectric accelerometers. These sensors, which generally have a frequency response from 10 Hz through 15 Khz, are excited with constant current excitation, typically around 400 microamps. Because these sensors use constant current excitation, wire resistance does not affect the calibration (unlike some competitor's charge-mode accelerometers). Therefore, longer wire lengths may be used. In fact, your wire length can safely reach 100 feet without adverse effect. Distances longer than 100 feet may exhibit loss of dynamic range due to capacitance loading. This is described in the excerpt from the PCB catalog, "SVS Shock & Vibration Catalog, #300A, pages 108 through 110. (Copywright 1999. Used by permission.) In order to use the formulas described in this document, use an excitation current of 400 microamps, and a bias voltage of 3.2 volts.