Sensors and ActuatorsChapter 4

ME 392February 13, 2012

week 5

Joseph Vignola

Sampled Time Histories

Two weeks back we talked about samples time histories

Frequency Spectra

Two weeks back we talked about samples time histories And last week we discussed that any time history made up discreet amounts of specific frequency components.

Frequency Spectra

Two weeks back we talked about samples time histories And last week we discussed that any time history made up discreet amounts of specific frequency components. The frequency spectrum tells us how much

of each frequency is in the time history

Electronic Filter

The filter you built is an electronic device that suppress the frequency component above a “cut-off” frequency.

Electronic Filter

The filter you built is an electronic device that suppress the frequency component above a “cut-off” frequency.

Other filters can be constructed to suppress frequency below a cut-off frequency…

Electronic Filter

The filter you built is an electronic device that suppress the frequency component above a “cut-off” frequency.

Other filters can be constructed to suppress frequency below a cut-off frequency…

Or around a frequency

Electronic Filter

The filter you built is an electronic device that suppress the frequency component above a “cut-off” frequency.

Other filters can be constructed to suppress frequency below a cut-off frequency…

Or around a frequency

Or everything but the spectral content around a specific frequency.

Electrical Transfer Functions

By establishing the ratio of the FFTs of the output and input of a circuit we can predict the output of a circuit given an input.

Then we can say that for any other input

Then we can say that for any other input

Mechanical Transfer Functions

Mechanical systems responded to forces or electrical inputs in a way that can be predicted by a transfer function

Sources

A loudspeaker converts an electrical signal to a quickly changing pressure field.

A shaker is a device that is a lot like speaker but outputs a force and is used for shaking things

Taken from www.school-for-champions.com

Other Sources

A laser is also a source.

An antenna is a source

Any device that has an electrical signal input and outputs a related for quantity

Taken from www.gearlive.com

Taken from atechfabrication.com

The related quantity can be a Force MotionSome form of heat

Linear Sources

A source is a linear source if there is a simple proportionality that relates the input.

Often we express the sensitivity as a transfer functionThis can either be a graph or a number that represents the behavior in a operational band For our speaker maybe something like

Taken from www.wilcoxon.com

Sensors

Sensors are used to measure. We will uses Force sensors AccelerometersStrain gauges Pressure sensorsBut there are all kinds of sensors

Taken from www.pcb.com

A force sensor creates a voltage proportional to an input force

Sensors

Sensors are used to measure. We will uses Force sensors Accelerometers Strain gauges Pressure sensorsBut there are all kinds of sensors

Taken from www.pcb.com

An accelerometer creates a voltage proportional to an input acceleration

But remember to convert this by multiplying

Sensors

Sensors are used to measure. We will uses Force sensors Accelerometers Strain gauges Pressure sensorsBut there are all kinds of sensors

Taken from www.sensorland.com

A strain gauge ultimately creates a voltage proportional to strain

Strain is dimensionless

Signal Conditioning

The hitch with most sensors is that they are not able to produce much (if any) electrical signal on there own.

Taken from www.pcb.com

For many sensor we need to use some other device between the sensor and the computer.

This could be aSignal conditionerA preamplifier / power supply Wheatstone bridge

Signal Conditioning

The hitch with most sensors is that they are not able to produce much (if any) electrical signal on there own.

Taken from www.b&K.com

For many sensor we need to use some other device between the sensor and the computer.

This could be aSignal conditionerA preamplifier / power supply Wheatstone bridge

Signal Conditioning

The hitch with most sensors is that they are not able to produce much (if any) electrical signal on there own.

For many sensor we need to use some other device between the sensor and the computer.

This could be aSignal conditionerA preamplifier / power supply Wheatstone bridge

Connectors

The connectors we use in the lab are

3.5mm or stereo mini