Miniature DeltaTron® Accelerometers Types 4507 and 4508 consist of a ThetaShear® accelerometer and a DeltaTron preamplifier in a lightweight titanium housing with integrated 10 - 32 UNF connectors. Types 4507-C and 4508-C are similar to the DeltaTron accelerometers but come without the preamplifier.
Design
The 10 - 32 UNF connector is an integrated part of the top piece, which also contains the preamplifier (not 4507 C or 4508 C). The slotted cylindrical stanchion holds a central seismic mass flanked by two piezoelectric plates. This assembly is clamped rigidly by a ring. The parts are firmly held together without the use of any bonding agent other than friction, a principle which has proved extremely reliable in Brüel & Kjær DeltaShear® accelerometers. This assembly is hermetically welded to the titanium housing.
DeltaTron® Accelerometers
DeltaTron is a generic name for accelerometers and signal-conditioning products from Brüel & Kjær. It identifies products that operate on a constant-current power supply and give output signals in the form of voltage modulation on the power supply line. One of the advantages of this system is that it allows you to use inexpensive cables.
Accelerometers Types 4507 and 4508 can be used with all vibration setups with DeltaTron or ICP® input modules.
The built-in, low-noise preamplifiers are made using thick film technology. They comprise ASICs including a special reference voltage that ensures very stable bias voltage over the entire operating temperature range.
The low output impedance means that you can connect long cables between the accelerometer and measurement equipment.
DeltaTron® Power Supply
WB 1372 is a cost-effective and reliable single-channel, battery-operated power supply for DeltaTron® accelerometers. The frequency range covers the full frequency range for the accelerometers and the transducer current is 3 mA ± 20%. Both input and output have BNC connectors.
Frequency Response
The following information on frequency response is included on each accelerometer’s accompanying calibration chart. However, certain accelerometers have this information built in electronically (TEDS) as well.
The upper frequency limits given in the specifications are the frequencies where the deviation from the reference sensitivity is less than 10%. It is approximately 30% of the mounted resonance frequency. This assumes that the accelerometer is correctly mounted on the test structure - a poor mounting can have a marked effect on the mounted resonance frequency.
The lower frequency limits and phase response are determined by the built-in preamplifiers. The lower frequency limits are given in the specifications for deviations from reference sensitivity of less than 10%.
Increased measurement accuracy can be achieved by dividing the actual measurement by the individual frequency response.
Frequency response curves generated from the individual TEDS values are given on the calibration chart for the major part of the frequency range. At low frequencies, the curves given are typical.
The calibration chart also includes these individual TEDS values that, together with a general formula, best fit the measured frequency response. The expression can be used for frequency response compensation in the specified frequency range.
Calibration
Each accelerometer is individually calibrated and supplied with a comprehensive calibration chart. Long-term stability and reliability are ensured by artificial ageing during the production process. Field checking and system calibration are straightforward using Brüel & Kjær’s Hand-held Vibration Calibrator Type 4294.
Subsequent Calibration
Brüel & Kjær manufactures a range of equipment for frequency response, sensitivity and system calibrations.
For calibration of Types 4507/4508, Calibration Clip DV 0459 is available. Fig. 12 Calibration Clip DV 0459 Specifications: Material:Base - Stainless steel (hardened)Spring - Stainless steel spring Mounting surface diameter: 21 mm Mounting thread: 10 - 32 UNF Weight: 17 gram.
