The sensor being the first link of a measuring chain converts a physical measured quantity (e.g. pressure, distance, temperature) into an electrically measurable quantity (e.g. voltage, resistance). This is done by taking advantage of various electrical and / or physical effects.

 

INDIRECT MEASUREMENTS

You can only measure few quantities directly with DAQ systems (e.g. current, voltage). Therefore physical laws including a current or voltage relation are applied (indirect measurements). A resistance measurement for example is done by connecting a resistor to a constant current source and measuring the voltage drop. The resistance results from the division of the measured voltage through the applied current. This principle is also used by multimeters.
 

SENSOR ADJUSTMENT

As you see, sensors "translate“ physical into electrical quantities. To connect them to a measuring system, the output must correspond in unit and codomain with the input of the measuring device. This is done by electrically transforming and / or amplifying the signal of the passive sensor with a measuring converter or amplifier.
 

ACTIVE SENSORS

In many sensors, this electronic function is already included and they need their own power supply. Those sensors are called active sensors, as they convert the measured quantity into a measurable electrical quantity themselves.

 

PHYSICAL MEASURED QUANTITIES

The following list of sensor types exclusively applies to analog measured quantities, as we focus on analog measurement technology.

Measured Quantity	Physical Phenomenon	Sensor Type	Comments, Examples
temperature	temperature dependance of resistance	PT100, PT1000, NTC, PTC	nonlinear element
temperature	Seebeck effekt (thermoelectric voltage)	thermocouple	large measuring range, nonlinear element
temperature	temperaturedependance of semiconductors	diodes, transistors	also available as active sensor
temperature	pyroelectric effect		for temperature change only
pressure, tension	piezoelectric effect	piezoelectric element	for force and pressure changes only
pressure, tension, torque moment	resistance dependance of the conductor shape	strain gauge (DMS)	usually connect as measuring bridge
position, length, angle, distance	inductivity change of a coil when inserting a metal piece LVDT	LVDT, differential choke	measurement with carrier frequency procedure
position, length, angle, distance	binary encoded angle and distance sensors	angle encoder	incremental or absolute; output digital
angle, distance	linear potentiometer, rotary encoder	potentiometer	analog output signal
magnetic induction	echo voltage with constant current	echo sensor	available as active integrated wiring
acceleration, velocity	tension of metal plates in semiconductor component	semicond. strain gauge	uni- or multidimensional sensor
acceleration, velocity	piezoelectric effect with a seismic mass	piezoelectric element	e.g. airbag sensor
luminous intensity	photonic stimulation of semiconductors	photodiode, phototransistor	available as passive and active sensors
luminous intensity	change of self-conductivity	photoresistor
current	voltage drop at a resistor	shunt	galvanic connection to the meas. current
current	measurement of the Hall	echo sensor	el. isolated from the meas. current
humidity	semiconductors, capacitive sensors		passive elements
sound, sound level	electrodynamic and capacitive microphones	microphones
filling-level	capacitive and optical measurement		active sensors
rotational speed	optical and inductive processes	speed encoder	digital and analog sensors
motion	optical and inductive processes	motion detector

 

MANUFACTURERS OF SENSORS

The following table provides a small selection of sensor manufacturers. This is just a selection and does not imply any judgement.
Please note that we are not responsible for the contents of the linked sites and we do not check them regularly. In many cases, the mentioned semiconductor manufacturers do not have their own sales department.

MANUFACTURERS OF SEMICONDUCTORS
Name	Tension, Pressure	Acceler- ation	Force, DMS	Temp., Humidity	Angle, Distance	Laser, Optical	Gas	Inductive, Echo	Quality
Analog Devices		x		x				x	simple
Aktiv Sensor (EPCOS)	x								medium
Amsys	x								medium
Analog microelectronics	x				x				medium
Infineon	x			x				x	simple
Panasonic Electric Works	x	x		x		x		x	simple
Sensata (Texas Instruments)	x	x					x		simple
Texas Instruments				x		x			simple
MANUFACTURERS
Name	Tension, Pressure	Acceler- ation	Force, DMS	Temp., Humidity	Angle, Distance	Laser, Optical	Gas	Inductive, Echo	Quality
AB-Elektronik	x			x					high
ACO Automation Components				x					high
Afriso-Euro-Index				x			x		high
Airflow	x			x					high
Altmann potentiometer					x				high
Ametek	x			x					high
ASM		x		x	x			x	high
AST	x		x						high
Baumer electric	x		x		x	x		x	high
BCM Sensor	x		x						high
BD Sensors	x								high
B.I.O-Tech								x	high
BLH (Vishay BLH)			x						high
B+S Multidata		x							high
Burster	x	x	x		x			x	high
disynet (German website)	x	x	x		x				medium
E+E				x			x		high
electrotherm				x					high
HBM (Hottinger)	x		x		x			x	high
Huba control	x		x						medium
HYGROSENS (B+B Thermo-Technik)				x					high
Jumo	x			x			x		high
Megatron			x		x				high
Messotron					x			x	high
Micro-Epsilon					x	x		x	high
SEIKA		x							high
Sensitec					x			x	medium
Sensor Technics	x		x						high
TC Direct				x					medium
TWK					x	x		x	high
WIKA	x			x					high
DISTRIBUTORS
Name	Tension, Pressure	Acceler- ation	Force, DMS	Temp., Humidity	Angle, Distance	Laser, Optical	Gas	Inductive, Echo	Quality
ALTHEN GmbH	x	x	x		x				high
BMC IGmbH Berlin	x	x	x	x	x		x	x	high
Conrad	x			x	x	x	x	x	simple
Farnell	x	x	x	x	x	x	x	x	medium
LASER Components						x			high
OMEGA	x		x	x		x			high
RS Components	x	x	x	x	x	x	x	x	medium