Tandem-Piezo design - the benefits

The unique features of PRUFTECHNIKs patented Tandem-Piezo accelerometers make them suitable for virtually all areas of applications in industrial environments.

The unique design practically eliminates temperature shock and base strain effects; it also handles condition evaluation of turbo machinery and gearboxes, anti-friction bearings and pump cavitation - all with the same transducer, thanks to a wide linear range and a defined shock pulse resonance characteristic at 36 kHz.

The built-in current line drive amplifier ensures immunity to ground looping and extremely low signal loss, even over long transmission distances, as well as compatibility with the entire PRUFTECHNIK line of mobile data collectors, FFT analyzers and online or remote condition monitoring equipment.

Despite the technologically advanced tandem-piezo design, these sensors are more economical than conventional compressor sensors. 

Tandem-Piezo accelerometer at a glance:

• Low base strain sensitivity
• Low sensitivity to temperature transients
• Built-in ‘Linedrive’ amplifier offers unsurpassed immunity against cable noise and ground loops
• Low transverse sensitivity
• High shock resistance
• Integrated resonance suppression filters avoids amplifier overloading
• Factory burn-in for high long-term stability
• Intrinsically safe version also available

Tandem-Piezo accelerometer design

Current Line Drive (CLD) - the advantages

The long cables used in permanently installed monitoring systems must stand up to considerable electrical and mechanical interference. With traditional sensors the signals barely get through the network, being drowned out by the noise and interference.

The solution: use either expensive high-quality cable carefully laid away from interference sources or a ‘line drive’ system, which consists of a tiny electronic amplifier built into each sensor which boosts the vibration signal.
The latter offers several advantages:

• Low sensitivity to mechanical and electrical interference (cable noise, electromagnetic sources, ground looping)
• Very long low-cost cables possible with very little signal loss
• Cable positioning during installation is not as critical
• Power supply current carried along the very same coaxial cable carrying the vibration signal (power comes from a source built into the receiver instrument).

There are two types of line drive systems, providing either voltage output or current output. PRUFTECHNIK systems use the latter, since it is a superior system with more sophisticated electronics and the following significant advantages:

• Much lower high frequency loss in very long cables even over 1000 meters.

• Much lower susceptibility to induced noise and ground-loop noise, also obviating in most cases the need for insulated sensors.

High frequency loss in long cables
The PRUFTECHNIK current line driver system has much lower high frequency loss in long cables than voltage output systems. This is because the instrument has a significantly lower input impedance, and since the maximum frequency is inversely proportional to input impedance, the maximum frequency is greatly extended.

Ground looping and noise
The PRUFTECHNIK current line driver system has much lower susceptibility to induced noise and ground-loop noise than voltage output systems. This is because the very low instrument input impedance minimizes influence from electromagnetic fields. The instrument virtually 'shorts' the cable conductors.
This has the added advantage that, with the exception of frequency rectifier-governed motors and high-voltage motors, costly insulated sensors can be avoided, eliminating the problem of insulator capacitance.

Industrial accelerometers

Types VIB 6.10x, VIB 6.12x, VIB 6.13x, VIB 6.14x

• Standard accelerometers for PRÜFTECHNIK condition monitoring systems
• Tandem-piezo sensor
• Current line drive (CLD) signal amplification
• Mounting options: bonded, threaded, magnetic
• IP68 option
• Measures vibration acceleration, shock pulse (roller bearing condition), cavitation in pumps
• Intrinsically safe version available as option.

Technical data (excerpt)

Mini sensors

Types VIB 6.202, VIB 6.203

• Compact design
• Space-saving cable routing
• Economically priced
• Tandem-piezo measuring element
• Current line drive (CLD) signal amplification
• Mounting options: bolted, glued, magnetic
• Vibration acceleration, shock pulse (roller bearing condition), cavitation in pumps
• Intrinsically safe versions available.

Technical data (excerpt)

Accelerometers for low speed machinery

Types VIB 6.172, VIB 6.195

• For low running speeds: starting at 6 RPM (=0.1 Hz)
• ICP voltage output (VIB 6.172) or current line drive signal amplification (VIB 6.195)
• Mounting options: bolted, glued ,magnetic (VIB 3.423)
• ICP sensor also available with intrinsic safety.

Technical data (excerpt)

TIPTECTOR

Hand-held probe for mobile vibration measurements – VIB 8.606

• Good signal transfer due to optimized probe tip
• Extendable handle
• Tandem-piezo measuring element
• Current line drive (CLD) signal amplification
• Vibration acceleration, shock pulse (roller bearing condition), cavitation in pumps
• Intrinsically safe version available.

Technical data (excerpt)

Hybrid Triaxial Accelerometers for advanced online CMS

Types VIB 6.215, VIB 6.216

• Simultaneous vibration measurement in X, Y and Z direction
• Gravitational acceleration and vibration acceleration
• MEMS and Tandem-Piezo measuring element
• Bonded mounting
• ICP voltage output
• Only for VIBGUARD online CMS

Technical data (excerpt)

Triaxial Accelerometer for portable vibration analyzers

Type VIB 6.655

• Simultaneous vibration measurement in X, Y and Z direction
• Mounting via threaded connection or magnetic adapter
• ICP voltage output
• Only for VIBXPERT I and VIBXPERT II

Technical data (excerpt)

Hand-held accelerometer for vibration and temperature measurements 

Type VIB 6.162

• Vibration and temperature with one sensor
• Stable connection via magnetic adapter
• Tandem-piezo measuring element
• Current line drive (CLD) signal amplification
• Available only with intrinsic safety

Online Combi Sensor

Type VIB 6.163

• Vibration, bearing condition and temperature with one sensor
• Tandem-piezo measuring element
• Current line drive (CLD) signal amplification
• Threaded mounting
• Connected to online CMS (VIBNODE, VIBROWEB,...)

Technical data (excerpt)

For more information please refer to our sensor catalog.