ICP Accelerometer Options

Within the world of ICP® sensing there are some common options that can be applied to almost any typical accelerometer. Here’s a quick review of the most common options.  How many of them are you familiar with?  This list contains the PCB® model number prefixes and a brief description of the options.

Transducer Electronic Data Sheet (TEDS) option as per IEEE1451.4 (2004) standard ( http://standards.ieee.org/develop/regauth/tut/).  This adds a small digital memory chip to the internal sensor ICP electronics to allow it to communicate information such as its model number, serial number and calibration value to TEDS enabled ICP sensor signal conditioners and analyzers.  There are currently two sub-options within the PCB Group TEDS offerings. Remember that it is analyzer or software dependent what version of TEDS your system can read.  It is best to contact and discuss this with your system vendor before choosing which format to order with your TEDS accelerometer.  (Calibration Tip: TMS 9155 Automated Accelerometer Calibration System reads and writes all of the TEDS templates listed below.  If your current calibration system cannot handle TEDS there is also a stand alone read/write kit TMS model 400B76 which handles programming through a standard USB port.)

TLD = TEDS v1.0 standardized generalized format.  This is the IEEE approved standardized format and is the first format to consider when choosing your formatting for accelerometers.  This version writes information like the model number, manufacturer and serial number permanently into the programmable “write once” section of the memory chip.  The programmable rewriteable contains information such as the sensitivity, reference frequency, calibration period, as well as sensor specifics like polarity and weight.

T = TEDS v0.9 generalized format.  The format used for a few years during the formation and balloting of the standard.  Fundamental difference is that this preliminary version does NOT make use of the programmable write once section of the memory.  All data in this version is written into the programmable rewritable section of the memory.

M = Metric mounting; this feature changes the thread specification on accelerometer models with default English threads to the appropriate metric thread.  On models with UNF 5-40 thread the metric equivalent becomes M-3 x 0.5 and on models with 10-32 thread the metric equivalent becomes M-6 x 0.75 (aside: in industrial applications the IMI accelerometers are M-6 x 1.0).  Also remember that in there are already some specific model numbers (PCB 340 series accelerometers) for sensors with all metric threads, hex and connectors as standards. (Calibration Tip: Adaptors are available for the PCB/TMS model K394B30 precision air bearing calibration exciter to adapt to all common accelerometer mounting threads.)

HT = High temperature option for ICP sensor internal electronics.  This option increases the standard operating temperature from maximum 250 degree F (121 degree C) to 325 degree F (163 degree C).  For extreme temperature environments up to 900 degree F (482 degree C) like gas turbine vibration applications, there are special accelerometers like the PCB model EX600B13 differential accelerometer.  (Calibration Tip:  Trending and looking for declines in the bias voltage of an accelerometer can provide basic health monitoring for accelerometers exposed to prolonged operation at high temperatures.)

J = Ground isolation; Provides an electrically insulating layer to the sensor design so that the accelerometer can be stud mounted to the test structure preventing a potential ground loop forming through a conductive test structure.  Note that as a practical matter, most accelerometers that are adhesively mounted to a conducting test structure become electrically isolated through the combination of non-conducting adhesive and the electrically isolating hard-coat on the PCB adhesive mounting bases.  (Calibration Tip: The PCB/TMS model K394B30 precision air bearing calibration exciter provides electrical isolation for the sensors under test.)

P = Positive polarity; Provides a flipped crystal stack to invert the electrical output signal for acceleration.  This feature is sometimes ordered with PCB charge mode accelerometers to pair with legacy non-inverting charge amplifiers from other vendors.  PCB charge mode accelerometers have negative output so that when paired with the inverting characteristic of the PCB Modal 443B01 laboratory style charge amplifier, the pair provides a positive output.

W = Water resistant; Provides a series of “weatherizing” steps useful for prolonged outdoor use or limited underwater use.  Includes bonding of connector cable interface, silicone sealant and shrink wrap to protect connection signal path.  (Calibration Tip: As with any rigid cable or bulky connector, be sure to secure a service loop of cable with tape to strain relieve the connector and mounting during calibrations.)

In the industrial monitoring (machinery maintenance or process quality) world of vibration measurements, there are also options like:

TO = Temperature output; Adds an internal temperature sensor (10 mV/deg C) and another signal conductor/connector pin to allow for simultaneous temperature measurement within the accelerometer package. No additional voltage supply is needed as the temperature sensor is powered directly from the same ICP supply.

EX = Hazardous area approval; The sensor has been manufactured and approved for use in hazardous areas (contact factory for specific approvals).

As always, we’re here to help you.  If you have any questions on these or other accelerometers just contact your local  PCB group field application engineer.