|
Input / Output Devices
Servo Control Accelerometers
Frequency response is often the single most important issue in selecting accelerometers. A primary concern is whether response to static accelerations, such as gravity, is needed. If so, use a suspended-mass or servo control type. Suspended-mass types tend to be more durable than servo control units.
However, most applications do not really need static response. Instead, the response must simply be close to dc. Piezoelectric accelerometers have low (0.01 to 5-Hz) frequency cutoff but do not respond to static acceleration. At the high end of the frequency response spectrum (above a few thousand Hertz), only piezoelectric devices operate properly.
Another important consideration is g-level range. This determines the maximum g load a device can measure accurately. It also indicates the maximum acceleration that a device can withstand without damage or permanent scale shift. It should be noted that the maximum acceleration encountered can be substantially higher than expected, because of incorrect mounting or loose parts. Except for servo control accelerometers, other types withstand shocks over several thousand g.
Working temperatures can also influence selection. Piezoelectric accelerometers with separate charge amplifiers have the widest temperature ranges.
An accelerometer has a temperature stability specification, which influences performance. Temperature stability has two facets: thermal gain shift and thermal zero shift. Thermal gain shift tells how much temperature changes accelerometer sensitivity. This is usually expressed in percent of full scale per degree.
Thermal zero shift is the amount of accelerometer output shift caused by temperature changes with no acceleration applied. This is given in percent of full scale per degree.
Servo control accelerometers generally have the best temperature stability, but specific temperature ranges must be considered. Temperature shift is usually nonlinear over typical operating ranges. As might be expected, operating the device in a narrow temperature band minimized these effects. Depending on the device, full-scale changes over the rated temperature range vary from (0.1% to 10%). Some accelerometers also have ratings for storage temperature that differ from the operating temperature limit.
Pages: 1 2 3
Servo Control Accelerometers: Servo Control Information
Previous Page Next Page
|
