How to Draw a Systems Diagram Step-by-Step Instructions for a Simple Example

Basic Steps to Follow: Identify components of system: Things Events Measured Value/Data Characterize the behavior of the system components: Are they static? How do they change with time? Sketch graphs! Identify linkages and connections between components. Draw the linkages between system components, indicating feedback loops. As you draw components and connections on the diagram, make sure that you have included all of the relevant components. Add new components and connections as needed. Pay attention to the level of detail you are including – is a component or connection too specific for the diagram you are making? This list provides an introduction to the questions that one must ask about a system in order to draw a diagram of it. The instructor can use this list at the beginning and/or at the end of this presentation, to help students gain context about the types of things to keep in mind when engaging in a task such as this.

A Simple Example: Heating a Room

Step 1: Identify Components of the System Heater with on/off switch Room Thermostat (optional) Events: Turning on/off the heater Measured Value: Temperature of the room This slide includes items identified in Step 1 from the “Basic Steps to Follow” list.

Step 2: Characterize the Behavior of the System Components: Heater with on/off switch Room Thermostat Events: Turning on/off the heater Measured Value: Temperature of the room High Low T > set point, switch off T < set point, switch on This slide includes items identified in Step 2 from the “Basic Steps to Follow” list.

Steps 3 & 4: Identify and Draw Linkages Between Components (Without Thermostat): Enter Room Heater Switch On Warmed Room Time Temperature High Low This slide includes items identified in Steps 3 and 4 from the “Basic Steps to Follow” list, with the variation of not including a thermostat in the system. This shows a basic system without a thermostat regulating the temperature. The room will continue warming indefinitely! The sketched graph shows the predicted data that would be obtained from measuring the temperature.

T > set point, turn off Steps 3 & 4: Identify and Draw Linkages Between Components (With Thermostat): Time Temperature High Low Warmed Room Thermostat Heater Switch On Measure Temperature Enter Room This slide includes items identified in Steps 3 and 4 from the “Basic Steps to Follow” list, with the variation of including a thermostat in the system. This shows a basic system with a thermostat regulating the temperature the room will heat until it reaches a set temperature, and then the heater will cycle on and off to maintain a constant temperature. The sketched graph shows the predicted data that would be obtained from measuring the temperature. T > set point, turn off T < set point, turn on

Step 5: Consider Where Additional Detail Could Be Added: Warmed Room Thermostat Heater Switch On Flows of heated and cold air into/out of the room. How the heater works (i.e. switch on, current passed through element, fan blows air into room or switch on, burner fired to heat water, water circulated through pipes). Measure Temperature How the thermometer works. Enter Room How the thermostat works. This slide includes items identified in Step 5 from the “Basic Steps to Follow” list, with the variation of including a thermostat in the system. In this slide, attention is paid to where more detail could be added. No new components were required. The ovals with text show places where additional details (in the form of systems diagrams) could be added to make this a more complex picture. It is worth discussing that different people will interact differently with the system and may care about different aspects/levels of detail. For example: a person inhabiting the room may care about the level of detail shown, while a biologist or health professional may want to know more about how people move into spaces or perceive ambient temperature, an HVAC technician may want to know more about the working of the heater and the flows of air into/out of the room, and an electrical engineer might want to know how the thermostat works. The biological/physiological mechanisms for a person entering a room and sensing the temperature. T > set point, turn off T < set point, turn on

Basic Steps to Follow: Identify components of system: Things Events Measured Value/Data Characterize the behavior of the system components: Are they static? How do they change with time? Sketch graphs! Identify linkages and connections between components. Draw the linkages between system components, indicating feedback loops. As you draw components and connections on the diagram, make sure that you have included all of the relevant components. Add new components and connections as needed. Pay attention to the level of detail you are including — is a component or connection too specific for the diagram you are making?