Signal Devices
Inputs
Signal inputs
accepted by signal conditioners include DC
voltage and current, AC voltage and current, frequency and electric
charge. Sensor inputs can be accelerometer, thermocouple, thermostat, resistance thermometer, strain gauge or bridge, and LVDT or RVDT. Specialized
inputs include encoder, counter or tachometer,
timer or clock, relay or switch, and other specialized inputs. Outputs for
signal conditioning equipment can be voltage, current, frequency, timer or
counter, relay, resistance or potentiometer, and other specialized outputs.
Signal conditioning
Process
Signal
conditioning can include amplification, filtering, converting, range matching,
isolation and any other processes required to make sensor output suitable for
processing after conditioning.
Filtering
Filtering is the most common signal conditioning
function, as usually not all the signal frequency spectrum contains valid data.
The common example is 60 Hz AC power lines, present in most environments,
which will produce noise if amplified.
Amplif
Signal amplification performs two important functions:
increases the resolution of the input signal, and increases its signal-to-noise
ratio For example, the output of an electronic temperature sensor, which is probably
in the mill volts range is probably too low for an analog-to-digital converter (ADC) to process directly. In this
case it is necessary to bring the voltage level up to that required by the ADC.
Commonly used
amplifiers on signal on conditioning include sample
and hold amplifiers, peak
detectors, log amplifiers, antilog amplifiers, instrumentation amplifiers and
programmable gain amplifiers.
Isolation
Signal
isolation must be used in order to pass the signal from the source to the
measurement device without a physical connection: it is often used to isolate
possible sources of signal perturbations. Also notable is that it is important
to isolate the potentially expensive equipment used to process the signal after
conditioning from the sensor.
Magnetic or optic isolation can be used. Magnetic isolation
transforms the signal from voltage to a magnetic field, allowing the signal to
be transmitted without a physical connection (for example, using a
transformer). Optic isolation takes an electronic signal and modulates it to a
signal coded by light transmission (optical encoding), which is then used for
input for the next stage of processing.