General Instrumentation Questions
What is the different between an analog and digital signal?
An analog signal is infinitely continuous; a digital signal is quantitized or broken up depending on bit resolution.
Why is the bandwidth sometimes lower than the sampling rate?
In order to capture small details of a real world signal, higher sampling rates
are needed. Sampling rate is your time domain resolution.
How many sensors can be connected to instrumentation?
This is dependent on output impedance of excitation
circuitry. The parallel combination of resistive loads cannot be less than the minimum
required load on the given electrical output.
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What is a bit?
A bit of information represents either and “on” or “off” state.
What is bit resolution?
Bit resolution is the number of steps or possibilities for a given number of bits. For example an 4 bit number has 2 to the power 4 possibilities which equals 16 distinct possibilities.
What are “nibbles”, “bytes” and “words”?
A nibble = 4 bits, and byte = 8 bits and a word = 16 bits.
What does “kilo”, “mega” and “giga” mean in the digital domain?
Kilo is 1024, mega = 10242 , giga = 10243. Therefore 8kbytes means that we have 8 x 1024 = 8192 pieces of 8 bit information.
What is analog to digital conversion?
This is the process in which an analog signal is quantitized into a digital signal. Usually performed by a device known as an analog to digital converter.
What is sampling rate?
The number of times per second an analog to digital converter takes a readings and converts per second.
What is the Nyquist criteria?
In order to re-create an analog signal, the sampling rate must be at least twice the frequency of the source analog signal.
Why is sometimes the bandwidth lower than the sampling rate?
In order to capture small details of a real world signal, higher sampling rates are needed. Sampling rate is your time domain resolution.
Is sampling rate affected by electrical loads, such as impedance of a sensor?
Typically no, however in some multiplexed system sampling rate is divided equally among different channels.
What is bandwidth?
The span of input frequencies that a device is designed to operate within.
Why do I sometimes see a –3db cutoff frequency listed as a specification, what does that mean?
This is the point were the signal will attenuate to about 70.7% of the original signal, usually chosen as a marker in which to describe the bandwidth of a filter or device. The –3db is the smallest discernable step in volume that the human ear will distinguish.
What is frequency response?
Another term to describe bandwidth.
What is Output and Input Impedance?
Output impedance is the minimum resistive load on a electrical output that will not cause a voltage drop for a given voltage. Input impedance in the amount of resistive loading in an electrical input. Instrumentation typically has very high input impedance to reduce resistive errors.
What does filter settling mean?
If an instrument is subjected to an impulse signal, settling time is the time from peak value to zero value.
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