Ch. 3 24.) Explain why the signal is never attenuated in a current-loop system.  25.) Draw the circuit of a current-loop system. When Vin is 1 V, the loop current should be 5 mA. At all times, Vout should equal Vin.  28.) Explain the difference between earth ground and signal return.  30.) Find the current in a ground loop that is 200 ft long, has a wire resistance of 0.05 Ω/ft, and has a difference of 4 V between grounds.  38.) Find the total voltage drop in a 200-ft #20 twisted pair wire circuit carrying 100 mA. (Hint: The signal has to go out 200 ft and back.) Ch. 6 1.) A potentiometer with a total range of 350° is supplied with a voltage of 12 Vdc. Find the output voltage for an angle of 135°.  10.) An absolute optical rotary encoder has five tracks. How many bits is the output, and what is the resolution in degrees per state (that is, degrees per LSB)?  18.) A toothed-rotor sensor has 30 teeth. Find the rpm if the sensor outputs pulses at 100 Hz.  22.) A CK20-B tachometer is mounted piggyback to a motor with a 10:1 built-in gearbox (similar to Figure 6.27). Find the velocity of the output shaft when the tachometer outputs 2 V.  24.) Both optical and Hall-effect sensors can be used as proximity switches. Name one possible application for each.   28.) When a 200-lb man gets in his car, the car body sinks 1 in. What is the spring constant for the suspension system of the car?  36.) A semiconductor force sensor has a sensitivity of .2 V/lb. If a 3-lb force is applied to the sensor, what would the sensor output voltage be?  48.) Construct a temperature sensor using the LM35 with the following specifications: Supply voltage = 12 V, and output = 0.5 V/°C.