PLC Configuration and Programming - Lab Report Example

Summary This laboratory exercise adopted the use of an analog thermometer in measuring the temperature of input modules that pass through the programmable-logic controller (PLC). Using the A/D converter, one of the most common challenges that most students would experience in this particular laboratory exercise is the right way to calibrate the analog thermometer. In practice, temperature can be taken and recorded on a real-time basis or as a constant temperature. In the process of comparing the differences between the real-time and constant temperature taken from the analog thermometer, the student can decide whether or not it is necessary to employ hysteresis. Eventually, the thermostat found in the system will either make the motor run or initiate the need to create cooling and heating effects. In relation to this particular laboratory exercise, a state-based program has been created in order to prevent the clustering of the schematics. To sum it up, this report will focus on discussing how state-based ladder logic can be applied to a garage door. As such, its structure and operation will be tackled in details. Objective The main objective of this particular laboratory exercise aims to implement the use of a thermostat within the PLC system. Using state-based ladder logic program, it is possible to design and create a thermostat that is capable of switching and controlling the heating and cooling system of the PLC. As such, it is possible to program a specified temperature in the thermostat. Set-up of the Equipment 1. A PC that has Omron PLC programmer and is well-suited for a CP1L PLC unit. 2. A CP1L unit 3. A push button switch for the input 4. A unit of open-loop DC motor (without brush). 5. A unit of MAD11 Analog for the Omron PLC 6. A 12V sensor module (approximately 10mV/oC for the output) Testing Method Part 1 Under part 1, it was necessary to examine the safety issues associated with the laboratory exercise. To prevent the risks of shock during the process of connecting the hardware system, it was necessary to disconnect the AC power of the PLC unit. Likewise, it was necessary to enclose the motor using a protection box. Another way to ensure safety is to clear out all unnecessary items within the workplace environment prior to the actual programming of PLC. After observing all necessary safety procedures, the next step is to carefully identify the wiring connection of the equipment. Figure 1: The illustration presented above is the proposed design for thermostat. Below are list of explanations concerning figure 1: 1. Initialization: Refers to the state of the machine during the initial stage. 2. Neutral State: Refers to the state of the machine as it waits for either heating or cooling signal. 3. Heating State: Refers to the stage wherein the heating element has been turned on. At this stage, the machine is expected to compare the input temperature with the actual temperature which is equivalent to the range of 25oC and 27oC. Assuming that the temperature is below 25oC, the heating element of the machine would automatically switch on. Assuming that the temperature is higher than 27oC, the heating element found in the machine would automatically switch off. 4. Cooling State: Refers to the stage wherein the cooling system is working similar to a hysteresis. Assuming that the actual temperature is higher than 27oC, the cooling system would automatically switch on. Assuming that the actual temperature is below 25oC, the cooling system would automatically switch off until such time that it reaches the neutral state. Part 2: Initialization Stage: The following are the main processes used during the initialization stage: Assuming that the PLC has been made available online, the motor is expected to return back to its initialization state. It means that the machine would automatically reset the system back into its neutral state. It is under the neutral state wherein the machine would wait for the next input signal before it turns on either the heating or cooling element. Below is the diagram of the proposed initialization state: Based on the figure presented above, notice that the “P_First_Cycle” switch run through the the “first cycle flag” of the processor before it reaches the “#8003” of the PLC. This procedure is necessary so that that the system can control the thermometer module in such a way that the CPU could regularly update and record the real-time temprature during each cycle. As such, it is during the initialization stage wherein the programmer should clearly set a specified range of temprature the machine should read. It will also serve as a benchmark on whether or not the system should automatically turn on the heating or cooling devices. Basically, the matching registered bits are initially set in the binary as it formally decodes the data in the hex value of “#8003”. Eventually, the said number would automatically be shifted down to its destination. Based on the figure presented above, the destination is the “word for 102”. Heating State: The state of heating is similar to the way hystersis works. Each time the actual temperature is below 25oC, the heater automatically switches on. Likewise, each time the actual temperature is higher than 27oc, the heater automatically switches off. Each time the heating element is turned “ON”; the actual temperature is constantly being recorded and saved as a word file in its destination point “D0”. Eventually, the each temperature recorded in “D0” will be compared and contrast with the expected temperature of 25oC. Automatically, the heating state sets the signal “ON” each time the temperature is below 25oC. For instance, looking at the “12D” in hex, notice that the heater automatically turns “OFF” at the time the temperature is higher than 27oC. (i.e. see #145 in hex). The following is the formula used in the computation of the equivalent hex value: Temperature Conversion: Assuming that the expected benchmark temperature is at 25oC, the formula used in computing for the hex values are as follows: = Resolution of ΔV Output (Expected temperature)(Voltage in each centigrade increase in temperature mV/C0) Resolution of ΔV Output Note: The output range of analog thermometer was normalized based on the temperature ranges found in the A/D converter. Cooling State: Similar to a hystersis, the cooling state refers to a point wherein the cooling system turns “ON” each time the temprature is higher than 27oC and subsequently turns “OFF” each time the temperature is below 25oC. Based on the figure presented above, the compare block sets the cooling system of the motor “ON” after it reads that the actual temperature is higher than 25oC. Eventually, the figure is translated to “#145” found in the hex immediately after the conversion has been made. On the contrary, the cooler automatically turns “OFF” the fan each time the actual temperature is below 25oC” (i.e. …at point “#12D” found in the hex). Output Block: Operating based on the bits set by either the heating, cooling, or neutral block, the output block records the purely the output. Assuming that alarm flag has been turned “ON”, the Alarm found in the machine would also turns “ON”. Likewise, assuming that the cooling flag is “ON”, the motor also turns “ON”. As such, the output’s state block is presented below: Symbols: The symbols are actually used to label each of the recorded state in the memory. For instance, both the Cooling flag and the Alarm can be classified as bits in the memory. The “D0” can be classified as data register in the memory. Often times, “D0” values can be used when comparing the recorded temperatures with the current temperature. See example below: Discussion: The most challenging part of the laboratory experiment was to find ways on how it is possible to accomplish the analog input based on the reading module of the analog temperature. Using the A/D converter, these steps are necessary before one can successfully convert the data into a meaningful reading. Specifically the data gathered from the thermometer will have to be scaled based on the actual temperature range of input coming from the PLC. These steps need to be applied to the resolution coming from the PLC, A/D converter, and the thermometer. The use of the state-based design will enable us to effectively control the machine’s heating and cooling system. Furthermore, the state-based design can allow us to easily simplify the algorithm operations by creating less complicated ladder logic. The neutral state can use in gathering inputs and setting the machine to either heating or cooling state. Conclusion: When operating a system that has a cooling and heating effects, it is possible to design and create a thermostat based on hysteresis. In this particular laboratory exercise, the most interesting part is the process of calibrating the Analog input device using an A/D converter. In the process of doing so, it is possible to gather a more accurate reading. Read More