Chapter 11 - Fundamentals of Conventional and Computer-Based Control and Monitoring Systems

There are many options for controlling and monitoring a poultry house. Depending on the application and the needs of the use, the controls can vary from simple on-off switches to a fully automated computer-based control system. It is important that those involved in specifying or using control and monitoring systems for poultry houses understand the basic operations, capabilities, and limitations of existing equipment as well as the potential benefits and limitations of more advanced equipment. Since the primary application of control technology in a poultry house is for control of environment, this application will be used for most of the following discussion. Similar control and monitoring concepts could be applied to most other applications in a poultry house (e.g., feeder operation, water monitoring, egg counting, etc.).

Control systems for poultry houses can usually be classified as conventional or computer-based. Conventional controls include simple electromechanical devices such as on-off thermostats, pressure switches, single and multi-stage fan controls, and timers for light scheduling. Self-contained, solid-state controls are also available for these types of tasks. Most conventional electromechanical controls have sensors which must be located close to the control, they do not have displays for the controlled variable, and the user who wants to know how well the control is working must use a second device to monitor the conditions (e.g., a thermometer may be required for the typical electromechanical thermostat). In contrast, conventional solid-state controls do have displays for the controlled variable, but it is usually only a local display.

Computer-based controls have several advantages over conventional controls including the following:

1. They can be programmed for almost any desired type of control including simple on-off, proportional, time proportioning, diumal (e.g., a light program that varies lights in a house on a cycle similar to natural outdoor light), etc.
2. The control program can be set up with numerous logical interactions, e.g., turn the evaporative cooler on if the temperature is > 80°F and the humidity is < 70% or if the temperature is > 85°F regardless of the humidity.
3. Changes in control strategy require only a change in the program (software), whereas similar changes in conventional controls require re-wiring the system.
4. The computer-based control system can incorporate local and remote text, graphics, or animation displays of controlled or monitored conditions at selectable intervals. It can also record the conditions on removable or permanent disks, and on a print out.
5. The computer-based control system can be designed for phone access or networked to other computers by wired or wireless systems including one in the home.
6. The computer-based control system can be expanded to include other sensors, functions, houses, etc. in the future.
7. The computer-based control system has a high reliability and very few or not moving parts.

Advantages of conventional over computer-based controls include:

1. Conventional controls, especially the electromechanical ones, tend to be less susceptible to damage by electrical surges (although computer-based systems can be protected by appropriate surge suppressors).
2. Conventional controls are more readily available, easy to replace by unskilled labor and relatively cheap.

Considerations that need to be taken into account prior to selecting a control and monitoring system for environmental control include the following:

1. What control accuracy is needed?
2. Will the set points be fixed, cyclic or stepped?
3. How and where will the controlled variables (e.g., temperature, humidity, static pressure, light, etc.) be sensed by the controls and how will they be monitored and/or recorded?
4. Do the displays need to be local or remote or both?
5. Is it desirable to record some of the environmental parameters like temperature, humidity, and light level on a permanent record that can be used to develop trend graphs, etc.?
6. Is it likely that the producer will want to change the control strategy in the near future, and if so, will he/she be willing to re-wire the system to accomplish the new control strategy?
7. What is the potential for improving performance and minimizing losses with optimized control and monitoring of environment?
8. What is the potential for energy savings with optimized control?
9. Considering the risks of failure in critical parts of the system, what level of reliability is required?
10. What level of user friendliness is required?