10.5 Design a two-position controller that provides an output of  5 V  when a type-J TC junction reaches    and drops to a low of  0 V  when the temperature has fallen to . Assume a    reference.

We use the two-position controller shown in Figure 10.5. Then the output should be 5.0 volts when the temperature reaches and drops back to 0.0 volts when the temperature drops back to . Well, the Type J TC produces  at and for , assuming a reference. Suppose we use a differential amplifier with a gain of 100 so that the voltages become  and respectively. Then, according to the design associated with Figure 10.5, we have

This gives,, so we pick   and then . We use the following differential amplifier to condition the TC voltage and a simple divider to produce the 1.256 volt setpoint along with the circuit of Figure 10.5.

10.6 Figure  10.20  shows a drying oven for which the oven is either off with  0 V  input or on with 8 volts input. The thermistor properties are: resistance of  4.7  at    and  1.4  at   . It has a -dissipation constant. Design a two-position controller with trip points of   and   . Keep self-heating below   .

So we should use a  to be sure the self_heating is below the specification.

So it is necessary to use an inverter on the output of the comparator.

Let , we can set .

Then we can get the complete schematic.

10.12 Design a PD controller with a  140% PB  and a  0.2 -min derivative time. The fastest signal speed is  1 min . Measurement range is  0.4  to  2 V , and the output is 0 to  10 V .

 We use Figure 10.11 as our PD controller, so:

Suppose , we can get  ,  and .

10.14 A proportional pneumatic controller has equal area bellows. If 3- to 15 -psi signals are used on input and output, find the ratio of pivot distances that provides a  23 % PB .

10.18 Design a proportional controller for a 4 - to  20-mA , ground-based input, a 0 - to  9-V  output, zero-error output adjustable from 0 to  100 % , and    adjustable from 1 to 10 . Design so the setpoint can be selected in the range of 4 to  20 mA .

 

S10.2 A pneumatic proportional controller is designed as shown in Figure  10.13  such that    is  5 cm  and  is  2.5 cm . The setpoint is  50 kPa  and the effective areas of the bellows are   . The nozzle/flapper system has a pressure/displacement characteristic as shown in Figure  10.22 . With no error, the output pressure is  60 kPa.

a. What nozzle/flapper gap is required to support an output of  50 kPa  ?

Through figure 10.22, we can get that to fetch 50 kPa, the gap must be 1.2mm. 
b. With no error, how much force in newtons and pounds does the input bellows exert on the flapper?

c. Suppose the input increases to  60 kPa. What force is now required by the feedback bellows? What output pressure?

The output pressure is 70kPa.

d. What new gap is required? How much did the flapper move?

The nev gap need to be 1.05mm from Figure 10.22 and the flapper move