Familiarization with the Training System

Transcription

1 Exercise 1-1 Familiarization with the Training System EXERCISE OBJECTIVE In this exercise, you will familiarize yourself with the components of the training system that are used for the measurement and control of temperature. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Temperature processes The heat exchanging devices of the training system Heating unit. Cooling unit. DISCUSSION Temperature processes A temperature process can be defined as the operation(s) used to create a change in the temperature of a body. The body can be, for example, a substance or a material. Temperature processes can operate in either heating or cooling mode: In the heating mode, thermal energy is added to a body in order to increase its temperature. In the cooling mode, thermal energy is removed from a body in order to decrease its temperature. In either case, some kind of heat exchanging device must be used to transfer thermal energy from one body to another. The heat exchanging devices of the training system The Process Control Training System comes with two types of heat exchanging devices, which are a heating unit and a cooling unit. Heating unit Figure 1-10 shows the heating unit of the Process Control Training System. This unit is used to add thermal energy to the process water. Festo Didactic

2 Ex. 1-1 Familiarization with the Training System Discussion Figure The heating unit of the Process Control Training System, model AC line cord 2. Switch S1 3. Electric heating element 4. Cold water inlet 5. Hot water outlet 6. Serpentine copper tube 7. Cyclic cut-out switch 8. Manual control knob 9. Control input terminals 10 Festo Didactic

3 Ex. 1-1 Familiarization with the Training System Discussion The heating unit consists of a copper tube bent in a serpentine shape through which the water flows. Within the tube is a heating element made of two electrical conductors that convert electrical energy into thermal energy. This thermal energy transfers to the water flowing through the tube by conduction and forced convection. The water therefore leaves the tube at an increased temperature. There are two ways to control the amount of electrical power applied to the heating element of the heating unit: 1. By using the manual control knob on the front panel of the heating unit 2. By using an external 4-20 ma or 0-5 V controller, in which case the controller output must be connected to the proper control input terminals on the front panel of the heating unit. Selection between these two options is by means of switch S1 on the front panel of the heating unit. The heating element of the heating unit is protected against overheating by a high temperature cut-out switch. The switch will remove electrical power from the heating element if the flow rate of the water through the unit becomes too low and the temperature of the water becomes too high. The cut-out temperature is approximately 55 C (131 F). The cyclic cut-out switch will reset automatically when the temperature of the water falls back to normal. A click will be heard when the cyclic switch is tripped. Another click will be heard when the switch resets. a On previous heating unit models, a manual cut-out switch is also installed. This switch is used as a backup in the event that the cyclic switch fails to operate. It will trip only under exceptional circumstances. When the switch is tripped, it needs to be manually reset by pushing a button on the top of the switch. To access the reset button, unplug the heating unit and unscrew the two bolts to remove the plastic cover. Even if the heating unit is protected against overheating, electrical power should not be applied to the heating element in the absence of water flow through this unit. This means that the manual control knob of the unit should be turned fully counterclockwise or that the current or voltage applied by the controller to the control input terminals of the unit should be minimum (4 ma or 0 V) in the absence of water flow. Failure to do so might cause the heating unit to wear out prematurely. Cooling unit Figure 1-11 shows the cooling unit of the Process Control Training System. This unit is used to remove thermal energy from the process water. Festo Didactic

4 Ex. 1-1 Familiarization with the Training System Discussion Figure The cooling unit of the Process Control Training System, model Hot water inlet 2. Cold water outlet 3. Manual control knob 4. Control input terminals 5. Fins 6. Serpentine copper tube 7. Propeller fans The cooling unit consists of a copper tube bent in a serpentine shape through which the water circulates. As the water flows through the tube, thermal energy from the water transfers to the tube by convection and by conduction. Thermal energy from the tube then transfers to the air flowing across the tube by convection, causing the temperature of the water to decrease. This convection is forced by two propeller fans. The fans induce a continuous stream of fresh air across the tube, which maintains a substantial temperature difference between the tube and the air. The higher the rotational speed of the fans, the faster the stream of fresh air and, therefore, the higher the rate of thermal energy transfer between the tube and the air. Attached to the serpentine tube is a web of thin metallic fins that increase the surface of thermal energy transfer between the tube and the surrounding air, which further increases the rate of thermal energy transfer by forced convection. 12 Festo Didactic

5 Ex. 1-1 Familiarization with the Training System Procedure Outline There are two ways to control the rotational speed of the fan motors of the cooling unit: 1. By using the manual control knob on the front panel of the cooling unit 2. By using an external 4-20 ma or 0-5 V controller, in which case the controller output is to be connected to the proper control input terminals on the front panel of the cooling unit. Selection between these two options is by means of switch S1 on the front panel of the cooling unit. A second switch, S2, is used to select the mode of control of the rotational speed of the fan motors, which can be either direct or reverse: When S2 is set to the (direct mode) position, the rotational speed of the fan motors will vary in direct proportion to the control current or voltage applied to the control input terminals. The higher the control current or voltage, the higher the rotational speed. If the manual control knob is used to control the rotational speed of the fan motors, turning the knob clockwise will cause the rotational speed to increase. Conversely, when S2 is set to the (reverse mode) position, the rotational speed of the fan motors will vary in inverse proportion to the control current or voltage applied to the control input terminals. The higher the control current or voltage, the lower the rotational speed. If the manual control knob is used to control the rotational speed of the fan motors, turning the knob clockwise causes the rotational speed to decrease. PROCEDURE OUTLINE The Procedure is divided into the following sections: Overview of the components The heating unit. The cooling unit. The RTD probe and the RTD temperature transmitter. The thermocouple probes and the thermocouple temperature transmitter module. PROCEDURE Overview of the components 1. Figure 1-12 shows the components of the Process Control Training System that are used to measure and control temperature. Get these components from your storage location and place them on the work surface. Festo Didactic

6 Ex. 1-1 Familiarization with the Training System Procedure Heating unit Cooling unit Thermocouple temperature transmitter module RTD temperature transmitter Figure Components used to measure and control temperature. 14 Festo Didactic

7 Ex. 1-1 Familiarization with the Training System Procedure The heating unit 2. Examine the heating unit, model As mentioned earlier, this device is used to increase the temperature of the process water. The water is passed through a serpentine tube where it gains the thermal energy produced by a heating element. Draw the I.S.A. instrumentation symbol of the heating unit below, as silkscreened on the front panel of this unit next to switch S1. Heating unit: 3. According to the arrow heads in the heating unit symbol, which hose port (left / right) of the unit corresponds the cold water inlet? Which corresponds to the hot water outlet? Do not apply electrical power to the heating element of the heating unit in the absence of water flow through this unit. Failure to do so might cause the heating unit to wear out prematurely. The cooling unit 4. Examine the cooling unit, model As previously mentioned, this device is used to decrease the temperature of the process water. The water is passed through a finned serpentine tube where it is cooled by the stream of air produced by two fans. Draw the I.S.A. instrumentation symbols of the finned serpentine tube, fan motor drive, fan motor, and fans of the cooling unit in the space below, as silkscreened between the two hose ports on the front panel of this unit. Finned serpentine tube: Fan motor drive, fan motor, and fans: Festo Didactic

8 Ex. 1-1 Familiarization with the Training System Procedure 5. Make the settings shown in Table 1-2 on the cooling unit: Table 1-2. Cooling unit settings. Knob or switch Setting S1 2 Manual control knob S2 Fully counterclockwise 6. Power up the cooling unit. To do so, connect the 24 V dc power input terminals of this unit to the 24 V dc power supply, model 6360, as shown in Figure Connect the power supply to a wall outlet and set its power switch to I (on). Figure Wiring diagram for the cooling unit. 7. Observe that the fans of the cooling unit are rotating at a low, minimum speed, which corresponds to the current setting of the manual control knob of this unit. The cooling unit should not make much noise. 8. Turn the manual control knob of the cooling unit fully clockwise. What happens to the rotational speed of the fans? 9. Set switch S2 of the cooling unit to the " " position. What happens to the rotational speed of the fans? 10. Turn the manual control knob of the cooling unit fully counterclockwise. What happens to the fan speed? 11. Disconnect the cooling unit from the power supply to stop the fans. 16 Festo Didactic

9 Ex. 1-1 Familiarization with the Training System Procedure The RTD probe and the RTD temperature transmitter 12. Examine the RTD probe and the RTD temperature transmitter, model These devices are intended to be used conjointly to measure the temperature of the water in the column of the training system. The RTD probe contains a primary temperature sensing element called a resistance temperature detector, or RTD. When connected to the 100 RTD input of the RTD temperature transmitter, the RTD probe provides the transmitter with an electrical signal proportional to the temperature of its tip. The transmitter converts this signal into a current and a voltage of normalized range that are available at the transmitter 4-20 ma and 0-5 V outputs. The transmitter also has a calibrated output, labeled "CAL.", that provides a fixed voltage of 100 mv per sensed degree Celsius above 0 C (or 56 mv per sensed degree Fahrenheit above 32 F). 13. Power up the RTD temperature transmitter. To do so, connect the power input terminals of this module to the 24 V dc power supply, as shown in Figure Make sure the power supply is on. Figure Wiring diagram for the RTD temperature transmitter. 14. Connect the RTD probe to the 100 RTD input of the temperature transmitter. To do so, connect the red connector of the probe to the red terminal of the 100 RTD input, and the black connectors of the probe to the black terminals of this input, as shown in Figure Let the probe tip lie on the work surface. Festo Didactic

10 Ex. 1-1 Familiarization with the Training System Procedure Figure Connecting the RTD probe to the RTD temperature transmitter. 15. On the RTD temperature transmitter, set the INPUT switch at RTD. Connect a multimeter to the CAL. output of the RTD temperature transmitter. 16. According to the multimeter reading, what is the ambient temperature sensed by the RTD probe? 17. Tightly clench your hand around the tip of the RTD probe. The thermal energy from your hand being transferred to the tip should produce a visible increase in the multimeter reading. The thermocouple probes and the thermocouple temperature transmitter module 18. Now examine the thermocouple temperature transmitter module, model This module consists of four temperature transmitters, labeled TT1 through TT4. Each transmitter is intended to be used in conjunction with a thermocouple probe to measure the temperature of the water at the pressure ports on the components of the training system. As for the RTD temperature transmitter, each thermocouple temperature transmitter converts the signal from its thermocouple probe into a current and a voltage of normalized range that are available at the transmitter 4-20 ma and 0-5 V outputs. Each transmitter has a calibrated output, labeled "CAL.", 18 Festo Didactic

11 Ex. 1-1 Familiarization with the Training System Procedure that provides a fixed voltage of 100 mv per sensed degree Celsius above 0 C (or 56 mv per sensed degree Fahrenheit above 32 F). 19. Examine one of the four thermocouple probes. As Figure 1-16 shows, the probe has a rectangular polarized connector (a pin is larger than the other) that plugs into the input of any of the four thermocouple temperature transmitters. The other end of the probe, which has a male quick-connect fitting, can be plugged into the pressure ports on the components of the training system. Observe that the quick-connect fitting is terminated by a narrow alloy tube. This tube, called a thermowell, contains a temperature sensing element called a thermocouple junction. The thermowell permits the thermocouple junction to be inserted into a pressure port without mechanical stress and chemical damage. Figure Thermocouple probe. Festo Didactic

12 Ex. 1-1 Familiarization with the Training System Conclusion 20. Power up the thermocouple temperature transmitter module. To do so, connect the power input terminals of this module to the 24 V dc power supply, as shown in Figure Make sure the power supply is on. Figure Wiring diagram for the thermocouple temperature transmitter module. 21. Connect a thermocouple probe to transmitter TT1 of the thermocouple temperature transmitter module. Let the quick-connect fitting of the probe lie on the work surface. 22. Set the INPUT switch of transmitter TT1 at THERMOCOUPLE. Connect a multimeter to the CAL. output of this transmitter. 23. According to the multimeter reading, what is the ambient temperature sensed by the thermocouple probe? a A difference of ±1 C (1.8 F) between the ambient temperature currently measured with the thermocouple temperature transmitter and that previously measured in step 16 with the RTD temperature transmitter is acceptable. 24. Turn off the power supply. Return all components and leads to their storage location. CONCLUSION In this exercise, you familiarized yourself with the components of the Process Control Training System that are used to measure and control temperature. REVIEW QUESTIONS 1. What is temperature? 20 Festo Didactic

13 Ex. 1-1 Familiarization with the Training System Review Questions 2. What does "two-point scale" mean? 3. Name the four most common temperature scales. 4. What are the names of the three curves that meet at the triple point on the phase diagram of water? 5. Briefly describe the concept of thermal equilibrium. Festo Didactic