(4) A Potentiometer (POT) consists of a circular resistive strip and a wiper. Th

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(4) A Potentiometer (POT) consists of a circular resistive strip and a wiper. The wiper's tip contacts the strip and this contact point slides along the strip as the wiper shaft (i.e., the dial) is turned. Potentiometer's circuit symbol is shown as a resistor (between A and C terminals) and a pointer (B). This circuit can be analyzed as two resistors in series (R1 and R2) with the center point connected to B. The sum of the resistance R1 and R2 is constant i.c., the resistance of the strip from A to C. The ratio of R1 and R2 varies with the dial angle. If the dial is all the way to the left (CCW), R2 is zero. If the dial is exactly at half way R1 R2. If the dial is turned all the way to the right (CW), R1 0. Wiper Contact (turn with dial) R1 B Vs R2 R2 Potentiometer (POT) If we connect the terminal A and C across a voltage source Vs, the voltage between the B and C (i.cthe output voltage Vo) is related to Vs by the voltage division formula. The ratio between RI and R2 (and the ratio between Vs and Vo) depends on the dial angle. This device is used in volume control in many home electronics (radio, TV, stereo amplifier, etc) In these applications, Vs is the signal source (from a microphone, see figure below, for example) and Vo is connected to an amplifier POT is also used as an output voltage Vo, we can tell the angle of the shaft. This is used in applications such as robotics and automotive where mechanical angle need to be measured and processed by a computer In this application, the voltage Vs is a known fixed value (eg., 10v). From the 10 Va controlle In a robotic application, a 10k POT (10k-10000, the resistance between A and C) is used in sensing the turning angle of a oint of a robotic arm. The POT has an end-to-end mechanical motion range of 120 degrees. When the POT is turned all the way to the CCW direction (0 angle), the output voltage is Ov. When it is all the way to the CC direction (120 degree angle), the output voltage is 10v In this installation, according to the voltage division formula, when the output voltage is exactly 5v, the angle should be exactly 60 degree but it is NOT! After some investigation, the engineer realized that it is due to the fact that the controller has an input resistance of 50kn. This 'crror can be fixed in software but the engineer needs to know the relationship between Vo and the angle of the joint. What is the actual angle when the voltage Vo is 5V in this case? Answer

Explanation / Answer

Here 50K will come in parallel to R2.So instead of R2 parallel combination of 50K and R2 will come.

5/10=(R2||50K)/[(R2||50K)+R1]

R1+R2=10K;

Put R2=10K-R1;

solving above equation,we get

R12-110K*R1+500*106=0

Roots of above equation are R1=10.5K or R1=4.75K

Since R1+R2=10K ,R1 alone can not be greater than 10K.

Therefore R1=4.75K

600 --->5K

X0 --->4.75K

Acutual angle is 570

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