Direct measurement using Tachometer PDF

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SENSORS DESCRIPTION...

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Direct measurement using TACHOMETER( A RPM sensor)-

RPM sensors A sensor is essential to sense shaft speed. Typically, devices used for this purpose are shaft (rotary type) encoders, photoelectric (optical type) sensors and magnetic rotational speed (proximity type) sensors. All of these sensors send speed data in the form of electrical pulses. Shaft encoders offer a high resolution of typically 1-5000 pulses per revolution (PPR) and clearly defined, symmetrical pulses. Proximity sensors provide medium (or low) resolution sensing, depending on the number of pulses measured per revolution. Photoelectric sensors usually sense a reflective target on the rotating shaft. Magnetic rotational speed sensors use various magnetic proximity measuring principles to monitor the speeds of machine components in a range between 0 and 30,000 rpm.

TACHOMETER(RPM sensor) A tachometer is a device used to measure the RPM or Revolutions Per Minute of any rotating body. Tachometers can be contact based or non-contact ones. The non-contact or contact-less optical tachometers usually use laser or Infrared beam to monitor the rotation of any body. This is done by calculating time taken for one rotation.

WORKING PRINCIPLE

In principle, RPM sensors convert mechanical motion into electric pulses with or without direct contact when positioned near a turning rotor, gear, shaft or other regularly moving device. The resultant output signals are then fed to a digital counter, totaliser, tachometer, or other monitoring and control device.

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CALCULATION:

To calculate the actual RPM, we need the time taken for one revolution. And (millis() - time) is the time taken for one full revolutions. In this case , let t be the time taken for one full revolution , so the total number of revolutions RPM in 60sec ( 60*1000 millisecond ) is : rpm = 60*1000 / t * actualREV => rpm = 60*1000 / (millis() - time ) * REV/2 OR rpm = 30*1000 / (millis() - time) * REV;

BLOCK DIAGRAM:

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FEATURES AND APPLICATION • It can measure RPM over 20k • • • • • • • •

Sensor range extends upto 7~8 cm Displays Maximum RPM when left Idle Automatically toggles modes from "Idle" to "reading" Can be adjusted to match the ambient lighting conditions It is comparatively cheap and easy to build Can work without an LCD Programmable and supports customization Connect an SD card to the Arduino to keep logs

USES: Airplanes typically have one tachometer for each engine, and in those that use propellers, one is also needed for each. A plane's engines usually operate at higher RPMs than its propellers. By using separate instruments for the different parts, the plane's pilot or crew can know whether there is a problem with any particular part.

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Indirect Pressure Measurement on Hydraulic Components Through MEMS Strain Sensors Construction and working :In early MEMS systems a multi-chip approach with the sensing element (MEMS structure) on one chip, and the signal conditioning electronics on another chip was used. The latest generation ADXL2O2E is the world's smallest mass-produced, low cost, integrated MEMS dual axis accelerometer. Polysilicon springs suspend the MEMS structure above the substrate such that the body of the sensor can move in the X and Y axes. These fingers are positioned between plates that are fixed to the substrate. Each finger and pair of fixed plates make up a differential capacitor, and the deflection of the proof mass is determined by measuring the differential capacitance. This sensing method has the ability of sensing both dynamic acceleration (i.e. shock or vibration) and static acceleration. The differential capacitance is measured using modulation/demodulation techniques. After amplification, the X and Y axis acceleration signals each go through a 32 KOhm resistor to an output pin (Cx and Cy) and a duty cycle modulator (the overall architecture can be seen in the block diagram in Figure 3). The user may limit the bandwidth, and thereby lower the noise floor, by adding a capacitor at the Cx and Cy pin. The output signals are voltage proportional to acceleration and pulse-widthmodulation (PWM) proportional to acceleration. Using the PWM outputs, the user can interface the ADXL2O2 directly to the digital inputs of a microcontroller using a counter to decode the PWM.

BLOCK DIAGRAM

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USES:-

There are numerous applications for MEMS and Nanotechnology like in Biotechnology Medicine Communications Inertial Sensing.

2. From the graph,slope=(5.2/0.5) For 2.6V output voltage,displacement of the core=(0.5*2.6/5.2)V =0.25cm(Ans)

3. E(Young’s Modulus)=Stress/strain

For quarter bridge circuit, VG/VOX=(-G.F*E/4)*(1/(1+G.F*E/2) GF=2 E=100/(12.5*200*10^7) =4*10^-7 VG=(-2*4*10^-7)/4*(1/(1+(2*4*10^-7)/2) -2*12*10^-7 V=-2.4µV(ANS)...