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Endevco | Meggitt Sensing Systems

FAQ

What is the difference between a PE transducer and an IEPE transducer?

A Piezoelectric charge transducer (single-ended or differential) has a high impedance charge output (measured in pC/g) and typically utilizes a charge converter/amplifier to output a voltage representing the mechanical stimulus to the PE transducer (accelerometer, pressure transducer, force gage, etc). An Integral Electronic Piezoelectric (IEPE) transducer has a high impedance charge signal converted to a low impedance voltage within the transducer itself. The output from the IEPE transducer is a voltage representing the mechanical stimulus to the transducer, measured in mV/g. See Technical Paper TP320 for additional information.

How do you determine the accelerometer’s output polarity?

Refer to the accelerometer’s individual data sheet “Specifications Section” or click here for the “Ask the Expert” article.

Can a piezoelectric pressure transducer measure static pressure?

No. Piezoelectric pressure transducers, like piezoelectric accelerometers, have a low frequency cut-off. Piezoelectric transducers are considered AC coupled devices. When using a charge amplifier with this type of transducer, the low frequency response is determined primarily by the low frequency response of the amplifier. It is possible to measure quasi-static pressure by using a charge amplifier with a long time constant. This process will allow for short duration measurement and is not recommended for routine static pressure measurements.

What is the difference between a damped and undamped accelerometer?

Undamped piezoresistive accelerometers, like piezoelectric accelerometers, have virtually flat frequency response curves with no phase shift. Damped piezoresistive and variable capacitance accelerometers, on the other hand, have a specific frequency response and phase shift, depending on the damping coefficient and the damping material used (viscous, gas). Click here for the “Ask the Expert” article.

Why isn’t the sensitivity, of a piezoresistive accelerometer, twice as high with 10V excitation as it is with only 5 V excitation?

The excitation voltage and the output sensitivity are not truly ratiometric. The reason it is not directly proportional to excitation (whether a piezoresistive accelerometer or pressure transducer) is due to temperature compensation steps during the build process, which utilize resistive components unique to each serial number. The current flow or E/R drop across each leg of the bridge circuit will have a small variance relative to each serial number unit. Therefore each unit should be calibrated with the excitation voltage to be used for actual testing. Click here for the “Ask the Expert” article.

What is the narrowest pressure pulse I can measure with your pressure transducers?

Transducer rise time and the narrowest pulse which can be measured without distortion / ringing, is the pressure transducer’s flat response T= 1/0.2 fn Period t, that will cause5%) t =T/4. Click here for the “Ask the Expert” article.

What kind of signal conditioning do you offer?

Meggitt has signal conditioning for various accelerometer types (PE/IEPE, PR/VC) as well as bridge-type PR Pressure transducers. Go to “Products search“ then select Electronics – signal conditioners and amplifiers in the “Search by technology”, for a complete products listing.

What media can I expose my 85XX transducer to?

Generally speaking, clean, dry gas, silicon-based oils or neutral pH fluids can be used without issue. See Technical Paper TP338 for additional details and exceptions (distilled water, antifreeze, etc.) to this general rule.

Can I seal the vent tube on my 8510B transducer?

Yes, with the caution that the process of modifying the tube (pinching it closed or blocking the tube’s output), creates a sealed-gage transducer, which may possibly create a condition of a DC voltage offset on the backside of the diaphragm, when the transducer sees elevated temperatures. The air within the closed tube will expand with increasing temperature and can cause a DC offset on the diaphragm.

Can I connect my PE accelerometer directly to an IEPE conditioner?

No, not directly. The IEPE (integral electronic piezoelectric) conditioner is looking for a low impedance input signal, which has already been converted from a high impedance charge signal to a low impedance voltage. You can, however, utilize an in-line Remote Charge Converter (RCC) between the charge accelerometer (piezoelectric) and the IEPE power supply/conditioner. See model 2771C data sheet.

Can I use the low-noise cables with IEPE accelerometers?

Yes, IEPE transducers do not require low-noise cables, but if you already have such cables you can use them without any concern.

Can I purchase extra black storage boxes for my accelerometers?

Sorry, these storage boxes are not sold as an accessory item.

Can I use your piezoresistive pressure transducers beyond their rated pressure without damage?

Yes. Meggitt’s pressure transducers can be used up to the burst pressure identified on the data sheet. Although each transducer is identified with a particular full scale range, there is no absolute end to the scale, with the exception of burst. Burst pressure is a static pressure rating, not to be confused with a peak pressure greater than 30% of the transducers specified resonance frequency. Most Meggitt piezoresistive transducers have a specification showing the non-linearity at 3X the full-scale rating thus good linearity is possible when exceeding full scale. See TP277 for additional details on our sculptured diaphragm pressure transducers.

Can you recommend on an accelerometer mounting wax to be used in a low temperature environment (zero °C and below) or another easy removable mean for a curved surface?

Although we’re not actually sure what will happen with beeswax and petro wax at temperatures below freezing, we’re confident that both will lose a considerable portion of their adhesion properties. The cyanoacrylate adhesive that we recommend for temporary mounting, however, is rated for use down to -65 F (-54 C). It is Loctite 430. The solvent that works best with Loctite 430 is Loctite X-NMS.