Piezo Electric Accelerometer
With Built In Amplifiers And Filters - RD185W

The RD185W is a low cost piezo electric accelerometer designed for direct pcb mounting. It contains a two stage amplifier and filter circuit which conditions the signal from the sensor element to allow direct connection to a low cost A-D converter.

Key Features

0.2 to 500 Hz frequency response Built in amplifiers and filters Self test input Single 5v supply PCB mounting Rugged piezo electric design Direct connection to microcontroller Proven automotive technology Designed and manufactured in the UK Very low cost

Environment

All accelerometers produce unwanted outputs due to environmental inputs other than acceleration. The piezo electric sensor in the RD185W has been designed for minimum sensitivity to base strain and thermal transients. This reduces the size of spurious outputs caused by strain or bending of the pcb or rapid variations in the ambient temperature. A highly stable piezo electric material is used which has a low and repeatable variation of sensitivity with temperature. Internal compensation is employed to further reduce the overall variation of sensitivity across the full temperature range.

Frequency Range

The sensor element in the RD185W has a much larger output than traditional designs. This allows extension of the low frequency range down to 0.2Hz without recourse to expensive charge amplifiers, whilst retaining a good signal to noise ratio. The mechanical resonant frequency of the sensor element is well over 2kHz so the high frequency cut off of the accelerometer is determined by the built in 4 pole low pass filter.

System Interface

The RD185W has been designed to be connected directly to the input of a typical microcontroller on chip A-D converter and to be powered from the standard 5V supply. The output is biased to exactly 1/2 of the power supply voltage in the absence of any inputs and this bias voltage will vary in direct proportion to the supply. The comprehensive band limiting filters built into the RD185W ensure that in many cases there is no need for extra anti aliasing filters. The output amplifier can swing to within 0.2V of the supply - thus making the most of the dynamic range of 5V A-D converters.

Test Input

A test input is provided which can be used to determine that the RD185W and associated external signal processing components are functioning correctly. The test input injects a signal into the piezo electric sensor element via a small capacitor. Changes in the transfer function from this input to the system output may be analysed to detect component failures.

Customisation

Special versions of the RD185W can be produced to meet customers exact requirements. The frequency response can be set within the band 0.05Hz to 1000Hz and the sensitivity to almost any value required.

Output B, Supply = 5V, Temperature 15-25°C unless stated

	min	max	unit
Sensitivity (@40Hz)	0.95	1.05	V/g
Frequency response : ref 40Hz over full temperature range
@ 0.2 Hz	-3.0	+0.5	dB
@ 500 Hz	-3.0	+1.0	dB
Test input gain @ 40 Hz	0.1	0.2	V/V
Transverse sensitivity (@ 2Hz)		5	%
Operating Temperature	-30	+85	°C
Variation of sensitivity over temperature	-4	+4	%
Vatiation of test input gain over temperature	-35	+35	%
Noise 0.2Hz - 500 Hz		1	mV
Maximum acceleration (operate)	-2.0	+2.0	g pk
Maximum acceleration (survival, repetitive ½ sine)	-100	+100	g pk
DC Bias on output ( supply/2 )	-100	+100	mV
Supply Voltage	4.5	5.5	V
Supply Voltage ( test @ 25°C )	4.5	12	V
Supply Current ( supply = 5V )	6	8	mA
Case material	zinc alloy
Weight	22	26	g

32mm x 32mm x 10mm

If you would like to find out more, please contact us.

The RD185 accelerometer includes features which are the subject of world wide patents or patent applications. While the information contained in this document is believed to be accurate no responsibility can be accepted for its use, nor for any infringements of patents or other rights of third parties which may result from its use. Lamerholm Electronics reserve the right to modify performance specifications without notice.