Sensors for Moton and Poston Measurement Introducton An ntegrated manufacturng envronment conssts of 5 elements:- - Machne tools - Inspecton devces - Materal handlng devces - Packagng machnes - Area where the raw materal and fnshed products are handled Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
In an ntegrated producton envronment, the sensors nteract wth the controllers and provde a detaled status of the process. The controller sends sgnals to the actuators, whch respond accordng to the functons. Sensors based manufacturng systems consst of data measurement by numbers of sensors, sensor ntegraton, sgnal processng and pattern recognton. Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
Moton transducers are transducers used for the measurement of mechancal quanttes:- Force Pressure Dsplacement Flow rate Prmary transducer senses the prelmnary data and converts them nto another form, whch s then converted nto some usable form by secondary transducer. Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
The devces needed to measure moton are several types, are classfed as follows:- A - Potentometrc- esstance Stran Gauge Apply the prncple of change n the resstance of materal n the sensor. B - Inductance Based on the prncple of varaton of nductance, nducton varatons serve as a measure of dsplacement. C - Capactance Apply the prncple of capactance varaton between a set of plate assembles. Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
- A - esstance Transducers - Potentometrc Prncple. - Wheatstone Brdge Crcut Prncple. - Stran Gauge. Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 5
- Potentometrc Prncple A sprng s a smple example of a transducer. When a certan force s appled to a sprng, t stretches, and the force nformaton s translated to dsplacement nformaton Dsplacement y s proportonal to force F, whch can be expressed as F k. y Where F appled force y deflecton k constant Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 6
As an example of the sprng element, the force causes the sprng to extend, and the mechancal dsplacement s proportonal to the force. The sprng s consdered to be the prmary transducer that converts force nto dsplacement. The end of the sprng s connected to another electrcal transducer, whch senses ts dsplacement and transmts t as an electrcal sgnal, ths electrcal transducer s called a secondary transducer Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 7
A potentometer s a transducer n whch a rotaton or dsplacement s converted nto a potental dfference Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 8
Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 9
esstve Element k. r x out k. r. θ out. Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 0
The fgure shows the dsplacement of the wper of the potentometer causes the output potental dfference obtaned between one end of the resstance and the slder. Ths devce converts lnear or angular moton nto changng resstance, whch may be converted drectly to a voltage or current sgnal. If the movement of the slder s n a crcular path along a resstance element, then the rotaton nformaton s converted nto nformaton n the form of a potental deference The voltage across the wper of the lnear potentometer s proportonal to the dsplacement The output of the rotary transducer s proportonal to the angular movement Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
oltage across the wper of the lnear potental s measured n terms of the dsplacement x E x L Where E the voltage across the potentometer L s the full scale dsplacement X dsplacement The error, whch s called the loadng error, s caused by the nput mpedance of the output devces. Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
The measurement of the stran s an mportant consderaton n measurement The measurement s used as a secondary step of many process varables ncludng flow, pressure, weght and acceleraton If a pece of metal wre s stretched, t get longer and thnner and ts resstance ncreases. The greater the stran experenced by the wre, the greater the change n resstance Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
- Wheatstone Brdge Crcut Prncple Converts the change n resstance nto voltage output Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
-One of the resstance branches s the resstance of the sensor. -The sensor resstance changes as a functon of the measured varable. -In case the brdge s balanced, the voltage dfference between BC 0, and the current passng the measurement devce 0. 0 0 0 m Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 5
There are two dfferent methods for usng the Wheatstone brdge n order to measure the varaton of the resstance n the form of proportonal output voltage. Null Method Deflecton Method Null Method - represents the sensor whose resstance changes as a functon of the measured value. - s calbrated adjustable resstor. (varable resstor) - & are fxed and known for the crcut. -Intally the crcut s calbrated so that the balanced brdge condton s mantaned and no voltage s observed at BC. -If the sensor resstor changes as a functon of the measured varable. -Then; we adjust n order to mantan the balanced brdge condton. -Then; can be determned Ths method s not senstve to the changes n the supply voltage Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 6
Deflecton Method -For measurng tme varyng and transent sgnals. -The three resstors,,. are of fxed resstance. - s the resstance of the sensor. -As the sensor resstance changes, nonzero output voltage BC s measured. A - Assume that the voltage of the measured devce has nfnte nput resstance m, so that no current flows through t BC 0, m 0 To fnd the actual output voltage measurement o snce and Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 7
then o () Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 8 In the Wheatstone brdge applcatons wth sensors, the brdge s balanced at a reference condton,, and ntal values of the resstance arms are the same o o 0
Let O where s the varaton from the calbrated nomnal resstance By substtutng equaton n.() O O o Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 9 O O << then, O o o o,
B- Assume that the voltage of the measured devce hasn't nfnte nput resstance, but large fnte value, so that small amount of current flows through t m 0 To fnd the actual output voltage measurement Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology 0
Snce m 0 m m Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology
If we consdered the voltage drop along the closed path, m, equal to 0 0 m m Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology And for the closed path, m, equal to 0 0 m m
We can solve for m and notng that o m. m, and ntal values of the resstance arms are the same o o O ( ) O m Dr.-Eng. Hsham El-Sherf Electroncs and Electrcal Engneerng Department ELCT90, Sensor Technology