Types 4500-A and 4501-A are cubic piezoelectric ThetaShear® accelerometers. These cubic accelerometers have low sensitivity to extraneous environmental effects, which is achieved through the ThetaShear design. The accelerometers feature a 10 – 32 UNF connector. On Type 4500-A, It is positioned on the top surface, which is perpendicular to its main axis. On Type 4501-A, it is positioned on the side surface, which is parallel to its main axis.
The piezoelectric element used is the PZ 23 lead zirconate titanate element. The housing is aluminium.
Uses
- General purpose multi-axis vibration and shock measurements on low-mass structures and in confined spaces
- Excellent for applications where a large number of accelerometers are required
Features
- Low weight
- Low sensitivity to environmental factors
- Electrically insulated for ground-loop protection
- High resonance frequency
- The mounting clips are glued to the object, or fitted with double-sided, adhesive tape.
- A mounting clip with thick base can be modified, before use, to suit the mounting surface on the test object.
- A mounting clip with swivel base an a Spirit Level which makes it easy to align the accelerometer in order to retain the co-ordinate system.
Characteristics
This piezoelectric accelerometer may be treated as a charge source. Its sensitivity is expressed in terms of charge per unit acceleration (pC/g).
The ThetaShear design involves a slotted cylindrical stanchion holding a central seismic mass, flanked by two piezoelectric plates. This assembly is clamped rigidly by the cover. To ensure optimum accuracy and reliability, no bonding agent other than molecular adhesion is required to hold the assembly together. The ThetaShear design provides for a combination of highest measurement stability, excellent sensitivity-to-weight ration and low sensitivity to extraneous environmental effects.
A remarkable feature of the ThetaShear principle is the fact that the transverse resonance frequency is always outside the 10% frequency limit. This ensures minimum interference from orthogonal vibration components in the useful frequency range of the accelerometer. The ThetaShear design also provides excellent immunity to other environmental effects such as base strains, magnetic sensitivity and acoustic fields.
Mounting
Special effort has been put into making mounting as flexible as possible. The accelerometer housing has slots that allow the use of mounting clips. The accelerometers can be easily fitted or removed to or from a number of different test objects.
There are three major mounting possibilities:
Common Specifications for all Plastic Mounting Clips
Ground loop noise, particularly troublesome in multichannel measurements, is avoided by electrically insulating the sensing elements from the common body. Both Type 4500 A and Type 4501 A feature this electrical insulation with respect to signal ground and have a resistance of more than 10 MW.
The electrical insulation of Types 4500 A and 4501 A comes from the accelerometer’s fully hard-anodised common body, with insulation at the three cylindrical mounting holes. The hard anodised mounting surfaces provide additional insulation.
Cable Clamping
When using miniature accelerometers, the accelerometer cable can affect the measurement result because of forces exerted by the cable on the accelerometer connector. This can then cause amplitude irregularities in the output from the accelerometer at frequencies up to approximately 200 Hz. This can be reduced by using a flexible cable. To effectively reduce the problem at low frequencies, it is generally recommended to clamp the cable. One way of doing this is to make a small loop in the cable close to the accelerometer (max. diameter 30 mm) and clamp the cable beside the base of the accelerometer with mounting wax or double-sided tape. This also reduces the possibility of dynamically induced noise generated by the cable.
Calibration
The sensitivity given in the calibration chart has been measured at 159.2 Hz with an acceleration of 10 g. For a 99.9% confidence level, the accuracy of the factory calibration is ± 2%.
